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Airbyte Protocol

Goals​

The Airbyte Protocol describes a series of standard components and all the interactions between them in order to declare an ELT pipeline. All message passing across components is done via serialized JSON messages for inter-process communication.

This document describes the protocol as it exists in its CURRENT form. Stay tuned for an RFC on how the protocol will evolve.

This document is intended to contain ALL the rules of the Airbyte Protocol in one place. Anything not contained in this document is NOT part of the Protocol. At the time of writing, there is one known exception, which is the Supported Data Types, which contains rules on data types that are part of the Protocol. That said, there are additional articles, e.g. A Beginner's Guide to the Airbyte Catalog that repackage the information in this document for different audiences.

Key Concepts​

There are 2 major components in the Airbyte Protocol: Source and Destination. These components are referred to as Actors. A source is an application that is described by a series of standard interfaces. This application extracts data from an underlying data store. A data store in this context refers to the tool where the data is actually stored. A data store includes: databases, APIs, anything that produces data, etc. For example, the Postgres Source is a Source that pulls from Postgres (which is a data store). A Destination is an application that is described by a series of standard interfaces that loads data into a data store.

The key primitives that the Protocol uses to describe data are Catalog, Configured Catalog, Stream, Configured Stream, and Field:

  • Stream - A Stream describes the schema of a resource and various metadata about how a user can interact with that resource. A resource in this context might refer to a database table, a resource in a REST API, or a data stream.
  • Field - A Field refers to a "column" in a Stream. In a database this would be a column; in a JSON object it is a field.
  • Catalog - A Catalog is a list of Streams that describes the data in the data store that a Source represents.

An Actor can advertise information about itself with an Actor Specification. One of the main pieces of information the specification shares is what information is needed to configure an Actor.

Each of these concepts is described in greater depth in their respective section.

Changelog​

The Airbyte Protocol is versioned independently of the Airbyte Platform, and the version number is used to determine the compatibility between connectors and the Airbyte Platform.

VersionDate of ChangePull Request(s)Subject
v0.5.22023-12-2658Remove unused V1.
v0.5.12023-04-1253Modify various helper libraries.
v0.5.02023-11-1349AirbyteStateStatsMessage added.
v0.4.22023-04-1246AirbyteAnalyticsTraceMessage added.
v0.4.12023-08-1441 & 44Various bug fixes.
v0.3.62023-04-2134Add explicit AirbyteStreamStatus statue values.
v0.3.52023-04-1330Fix indentation.
v0.3.42023-04-1328Fix Indentation.
v0.3.32023-04-1218AirbyteStreamStatusMessage added.
v0.3.22022-10-2818875AirbyteEstimateTraceMessage added.
v0.3.12022-10-1217907AirbyteControlMessage.ConnectorConfig added.
v0.3.02022-09-0916479AirbyteLogMessage.stack_trace added.
v0.2.02022-06-1013573 & 12586STREAM and GLOBAL STATE messages.
v0.1.12022-06-0613356Add a namespace in association with the stream name.
v0.1.02022-05-0312458 & 12581AirbyteTraceMessage added to allow connectors to better communicate exceptions.
v0.0.22021-11-157798Support oAuth Connectors (internal).
v0.0.12021-11-191021Remove sub-JSON Schemas.
v0.0.02020-11-18998Initial version described via JSON Schema.

Actor Interface​

This section describes important details about the interface over actors. It reviews parts of the interface that are the same across all actors. It also describes some invariants for all methods in actor interfaces.

Common Interface Methods​

The following part of the interface is identical across all actors:

spec() -> ConnectorSpecification
check(Config) -> AirbyteConnectionStatus

These methods are described in their respective sections (spec, check).

Interface Invariants​

The output of each method in actor interface is wrapped in an AirbyteMessage. This struct is an envelope for the return value of any message in the described interface. See the section the AirbyteMessage section below for more details. For the sake of brevity, interface diagrams will elide these AirbyteMessages.

Additionally, all methods described in the protocol can emit AirbyteLogMessages and AirbyteTraceMessages (for more details see Logging). These messages allow an actor to emit logs and other informational metadata. All subsequent method signatures will assume that any number of messages of these types (wrapped in the AirbyteMessage) may be emitted.

Each method in the protocol has 3 parts:

  1. Input: these are the arguments passed to the method.
  2. Data Channel Egress (Output): all outputs from a method are via STDOUT. While some method signatures declare a single return value, in practice, any number of AirbyteLogMessages and AirbyteTraceMessages may be emitted. An actor is responsible for closing STDOUT to declare that it is done.
  3. Data Channel Ingress: after a method begins running, data can be passed to it via STDIN. For example, records are passed to a Destination on STDIN so that it can load them into a data warehouse.

Sources are a special case and do not have a Data Channel Ingress.

Additional Invariants

  • All arguments passed to an Actor and all messages emitted from an Actor are serialized JSON.
  • All messages emitted from Actors must be wrapped in an AirbyteMessage(ref) envelope.
  • Messages not wrapped in the AirbyteMessage must be dropped (e.g. not be passed from Source to Destination). However certain implementations of the Airbyte Protocol may choose to store and log unknown messages for debugging purposes.
  • Each message must be on its own line. Multiple messages cannot be sent on the same line. The JSON objects cannot be serialized across multiple lines.
  • STDERR should only be used for log messages (for errors). All other Data Channel Data moves on STDIN and STDOUT.

Common Interface​

Spec​

spec() -> ConnectorSpecification

The spec command allows an actor to broadcast information about itself and how it can be configured.

Input:​

  1. none.

Output:​

  1. spec - a ConnectorSpecification wrapped in an AirbyteMessage of type spec. See the Actor Specification for more details on the information in the spec.

Check​

check(Config) -> AirbyteConnectionStatus

The check command validates that, given a configuration, that the Actor is able to connect and access all resources that it needs in order to operate. e.g. Given some Postgres credentials, it determines whether it can connect to the Postgres database. The output will be as follows:

  • If it can, the check command will return a success response.
  • If check fails because of a configuration issue (perhaps the password is incorrect), it will return a failed response and (when possible) a helpful error message. A failed response will be considered as a config error, i.e. user error. Outputting a trace message detailing the config error is optional, but allows for more detailed debugging of the error.
  • If it fails because of a connector issue, the check command should output a trace message detailing the failure. It is not expected to receive an AirbyteConnectionStatus in this failure case.

If an actor's check command succeeds, it is expected that all subsequent methods in the sync will also succeed.

Input:​

  1. config - A configuration JSON object that has been validated using ConnectorSpecification#connectionSpecification (see ActorSpecification for information on connectionSpecification).

Output:​

  1. connectionStatus - an AirbyteConnectionStatus Message wrapped in an AirbyteMessage of type connection_status.

Source​

A Source is an application that extracts data from an underlying data store. A Source implements the following interface:

spec() -> ConnectorSpecification
check(Config) -> AirbyteConnectionStatus
discover(Config) -> AirbyteCatalog
read(Config, ConfiguredAirbyteCatalog, State) -> Stream<AirbyteRecordMessage | AirbyteStateMessage>

spec and check are the same as the commands described in the Common Commands section.

Discover​

The discover method detects and describes the structure of the data in the data store and which Airbyte configurations can be applied to that data. For example, given a Postges source and valid Config, discover would return a list of available tables as streams.

Input:​

  1. config - A configuration JSON object that has been validated using ConnectorSpecification#connectionSpecification (see ActorSpecification for information on connectionSpecification).

Output:​

  1. catalog - an AirbyteCatalog wrapped in an AirbyteMessage of type catalog. See the Catalog Section for details.

Read​

read extracts data from the underlying data store and emits it as AirbyteRecordMessages. It also emits AirbyteStateMessages to allow checkpointing replication.

Input:​

  1. config - A configuration JSON object that has been validated using ConnectorSpecification#connectionSpecification (see ActorSpecification for information on connectionSpecification).
  2. configured catalog - A ConfiguredAirbyteCatalog is built on top of the catalog returned by discover. The ConfiguredAirbyteCatalog specifies HOW the data in the catalog should be replicated. The catalog is documented in the Catalog Section.
  3. state - A JSON object that represents a checkpoint in the replication. This object is only ever written or read by the source, so it is a JSON blob with whatever information is necessary to keep track of how much of the data source has already been read (learn more in the State & Checkpointing Section).

Output:​

  1. message stream - An iterator of AirbyteRecordMessages and AirbyteStateMessages piped to the Data Channel Egress i.e: stdout.
    • A source outputs AirbyteStateMessages in order to allow checkpointing data replication. State is described in more detail below in the State & Checkpointing section.
    • Only AirbyteRecordMessages that contain streams that are in the catalog will be processed. Those that do not will be ignored. See Schema Mismatches for more details.
    • AirbyteRecordMessages from multiple streams can be multiplexed/mixed together, and do not need to be emitted serially as a group.

Destination​

A destination receives data on the Data Channel Ingress and loads it into an underlying data store (e.g. data warehouse or database).

It implements the following interface.

spec() -> ConnectorSpecification
check(Config) -> AirbyteConnectionStatus
write(Config, AirbyteCatalog, Stream<AirbyteMessage>(stdin)) -> Stream<AirbyteStateMessage>

For the sake of brevity, we will not re-describe spec and check. They are exactly the same as those commands described for the Source.

Write​

Input:​

  1. config - A configuration JSON object that has been validated using the ConnectorSpecification.
  2. configured catalog - A ConfiguredAirbyteCatalog. This is a modified version of the catalog returned by the discover command. Any AirbyteRecordMessagess that the destination receives that do not match the structure described in the catalog will fail.
  3. message stream - (this stream is consumed on stdin--it is not passed as an arg). It will receive a stream of JSON-serialized AirbyteMesssage.

Output:​

  1. message stream - A stream of AirbyteStateMessages piped to stdout. The destination connector should only output state messages if they were previously received as input on stdin. Outputting a state message indicates that all records which came before it have been successfully written to the destination. Implementations of this spec will likely want to move messages filtering and validation upstream of the destination itself
  • The destination should read in the AirbyteMessages and write any that are of type AirbyteRecordMessage to the underlying data store.
  • The destination should ignore fields or streams that are out of sync with the catalog. The destination should always make its best effort to load what data is there that does match that catalog. e.g. if the User Stream has the fields first_name and last_name in the catalog, but the record has first_name and eye_color, the destination should persist first_name, even though last_name is missing. It should ignore eye_color as extraneous.

This concludes the overview of the Actor Interface. The remaining content will dive deeper into each concept covered so far.

Actor Specification​

The specification allows the Actor to share information about itself.

The connectionSpecification is JSONSchema that describes what information needs to the actor for it operate. e.g. If using a Postgres Source, the ConnectorSpecification would specify that a hostname, port, and password are required in order for the connector to function. This JSONSchema can be used to validate that the provided inputs are valid. e.g. If port is one of the fields and the JsonSchema in the connectionSpecification specifies that this field should be a number, if a user inputs "airbyte", they will receive an error. For connection specification, Airbyte adheres to JsonSchema validation rules. The Airbyte implementation of the Protocol is able to render this JSONSchema to produce a form for users to fill in the information for an Actor.

The specification also contains information about what features the Actor supports.

  • protocol_version describes which version of the protocol the Connector supports. The default value is "0.2.0".
  • supported_destination_sync_modes - describes which sync modes a destination is able to support. See Sync Modes.

documentationUrl and changelogUrl are optional fields that link to additional information about the connector.

The following are fields that still exist in the specification but are slated to be removed as they leak choices about how Airbyte implements the protocol as opposed to being strictly necessary part of the protocol.

  • supportsIncremental is deprecated and can be ignored. It is vestigial from when full refresh / incremental was specified at the Actor level.
  • supportsNormalization determines whether the Destination supports Basic Normalization
  • supportsDBT - determines whether the Destination supports Basic Normalization
  • authSpecification and advanced_auth will be removed from the protocol and as such are not documented. Information on their use can be found here.
ConnectorSpecification:
  description: Specification of a connector (source/destination)
  type: object
  required:
    - connectionSpecification
  additionalProperties: true
  properties:
    # General Properties (Common to all connectors)
    protocol_version:
      description: "the Airbyte Protocol version supported by the connector. Protocol versioning uses SemVer."
      type: string
    documentationUrl:
      type: string
      format: uri
    changelogUrl:
      type: string
      format: uri
    connectionSpecification:
      description: ConnectorDefinition specific blob. Must be a valid JSON string.
      type: object
      existingJavaType: com.fasterxml.jackson.databind.JsonNode
    # Connector Type Properties (Common to all connectors from same type)
    # Source Connectors Properties
    supportsIncremental:
      description: (deprecated) If the connector supports incremental mode or not.
      type: boolean
    # Destination Connectors Properties
    # Normalization is currently implemented using dbt, so it requires `supportsDBT` to be true for this to be true.
    supportsNormalization:
      description: If the connector supports normalization or not.
      type: boolean
      default: false
    supportsDBT:
      description: If the connector supports DBT or not.
      type: boolean
      default: false
    supported_destination_sync_modes:
      description: List of destination sync modes supported by the connector
      type: array
      items:
        "$ref": "#/definitions/DestinationSyncMode"

Catalog​

Overview​

An AirbyteCatalog is a struct that is produced by the discover action of a source. It is a list of AirbyteStreams. Each AirbyteStream describes the data available to be synced from the source. After a source produces an AirbyteCatalog or AirbyteStream, they should be treated as read only. A ConfiguredAirbyteCatalog is a list of ConfiguredAirbyteStreams. Each ConfiguredAirbyteStream describes how to sync an AirbyteStream.

Each AirbyteStream of these contain a name and json_schema field. The json_schema field accepts any valid JsonSchema and describes the structure of a stream. This data model is intentionally flexible. That can make it a little hard at first to mentally map onto your own data, so we provide some examples below: _ If we are using a data source that is a traditional relational database, each table in that database would map to an AirbyteStream. Each column in the table would be a key in the properties field of the json_schema field. _ e.g. If we have a table called users which had the columns name and age (the age column is optional) the AirbyteCatalog would look like this:

{
  "streams": [
    {
      "name": "users",
      "json_schema": {
        "type": "object",
        "required": ["name"],
        "properties": {
          "name": {
            "type": "string"
          },
          "age": {
            "type": "number"
          }
        }
      }
    }
  ]
}

If we are using a data source that wraps an API with multiple different resources (e.g. api/customers and api/products) each route would correspond to a stream. The JSON object returned by each route would be described in the json_schema field.

e.g. In the case where the API has two endpoints api/customers and api/products and each returns a list of JSON objects, the AirbyteCatalog might look like this. (Note: using the JSON schema standard for defining a stream allows us to describe nested objects. We are not constrained to a classic "table/columns" structure)

{
  "streams": [
    {
      "name": "customers",
      "json_schema": {
        "type": "object",
        "required": ["name"],
        "properties": {
          "name": {
            "type": "string"
          }
        }
      }
    },
    {
      "name": "products",
      "json_schema": {
        "type": "object",
        "required": ["name", "features"],
        "properties": {
          "name": {
            "type": "string"
          },
          "features": {
            "type": "array",
            "items": {
              "type": "object",
              "required": ["name", "productId"],
              "properties": {
                "name": { "type": "string" },
                "productId": { "type": "number" }
              }
            }
          }
        }
      }
    }
  ]
}

Note: Stream and field names can be any UTF8 string. Destinations are responsible for cleaning these names to make them valid table and column names in their respective data stores.

Namespace​

Technical systems often group their underlying data into namespaces with each namespace's data isolated from another namespace. This isolation allows for better organisation and flexibility, leading to better usability.

An example of a namespace is the RDBMS's schema concept. An API namespace might be used for multiple accounts (e.g. company_a vs company_b, each having a "users" and "purchases" stream). Some common use cases for schemas are enforcing permissions, segregating test and production data and general data organization.

The AirbyteStream represents this concept through an optional field called namespace. Additional documentation on Namespaces can be found here.

Cursor​

  • The cursor is how sources track which records are new or updated since the last sync.
  • A "cursor field" is the field that is used as a comparable for making this determination.
    • If a configuration requires a cursor field, it requires an array of strings that serves as a path to the desired field. e.g. if the structure of a stream is { value: 2, metadata: { updated_at: 2020-11-01 } } the default_cursor_field might be ["metadata", "updated_at"].

AirbyteStream​

This section will document the meaning of each field in an AirbyteStream

  • json_schema - This field contains a JsonSchema representation of the schema of the stream.
  • supported_sync_modes - The sync modes that the stream supports. By default, all sources support FULL_REFRESH. Even if this array is empty, it can be assumed that a source supports FULL_REFRESH. The allowed sync modes are FULL_REFRESH and INCREMENTAL.
  • source_defined_cursor - If a source supports the INCREMENTAL sync mode, and it sets this field to true, it is responsible for determining internally how it tracks which records in a source are new or updated since the last sync. When set to true, default_cursor_field should also be set.
  • default_cursor_field - If a source supports the INCREMENTAL sync mode, it may, optionally, set this field. If this field is set, and the user does not override it with the cursor_field attribute in the ConfiguredAirbyteStream (described below), this field will be used as the cursor. It is an array of keys to a field in the schema.

Data Types​

Airbyte maintains a set of types that intersects with those of JSONSchema but also includes its own. More information on supported data types can be found in Supported Data Types.

ConfiguredAirbyteStream​

This section will document the meaning of each field in an ConfiguredAirbyteStream

ConfiguredAirbyteStream:
  type: object
  additionalProperties: true
  required:
    - stream
    - sync_mode
    - destination_sync_mode
  properties:
    stream:
      "$ref": "#/definitions/AirbyteStream"
    sync_mode:
      "$ref": "#/definitions/SyncMode"
      default: full_refresh
    cursor_field:
      description: Path to the field that will be used to determine if a record is new or modified since the last sync. This field is REQUIRED if `sync_mode` is `incremental`. Otherwise it is ignored.
      type: array
      items:
        type: string
    destination_sync_mode:
      "$ref": "#/definitions/DestinationSyncMode"
      default: append
    primary_key:
      description: Paths to the fields that will be used as primary key. This field is REQUIRED if `destination_sync_mode` is `*_dedup`. Otherwise it is ignored.
      type: array
      items:
        type: array
        items:
          type: string
SyncMode:
  type: string
  enum:
    - full_refresh
    - incremental
DestinationSyncMode:
  type: string
  enum:
    - append
    - overwrite
    - append_dedup # SCD Type 1 & 2
  • stream - This field contains the AirbyteStream that it is configured.
  • sync_mode - The sync mode that will be used to by the source to sync that stream. The value in this field MUST be present in the supported_sync_modes array for the discovered AirbyteStream of this stream.
  • cursor_field - This field is an array of keys to a field in the schema that in the INCREMENTAL sync mode will be used to determine if a record is new or updated since the last sync.
    • If an AirbyteStream has source_defined_cursor set to true, then the cursor_field attribute in ConfiguredAirbyteStream will be ignored.
    • If an AirbyteStream defines a default_cursor_field, then the cursor_field attribute in ConfiguredAirbyteStream is not required, but if it is set, it will override the default value.
    • If an AirbyteStream does not define a cursor_field or a default_cursor_field, then ConfiguredAirbyteStream must define a cursor_field.
  • destination_sync_mode - The sync mode that will be used the destination to sync that stream. The value in this field MUST be present in the supported_destination_sync_modes array in the specification for the Destination.

Source Sync Modes​

  • incremental - send all the data for the Stream since the last sync (e.g. the state message passed to the Source). This is the most common sync mode. It only sends new data.
  • full_refresh - resend all data for the Stream on every sync. Ignores State. Should only be used in cases where data is very small, there is no way to keep a cursor into the data, or it is necessary to capture a snapshot in time of the whole dataset. Be careful using this, because misuse can lead to sending much more data than expected.

Destination Sync Modes​

  • append - add new data from the sync to the end of whatever already data already exists.
  • append_dedup - add new data from the sync to the end of whatever already data already exists and deduplicate it on primary key. This is the most common sync mode. It does require that a primary exists in the data. This is also known as SCD Type 1 & 2.
  • overwrite - replace whatever data exists in the destination data store with the data that arrives in this sync.

Logic for resolving the Cursor Field​

This section lays out how a cursor field is determined in the case of a Stream that is doing an incremental sync.

  • If source_defined_cursor in AirbyteStream is true, then the source determines the cursor field internally. It cannot be overridden. If it is false, continue...
  • If cursor_field in ConfiguredAirbyteStream is set, then the source uses that field as the cursor. If it is not set, continue...
  • If default_cursor_field in AirbyteStream is set, then the sources use that field as the cursor. If it is not set, continue...
  • Illegal - If source_defined_cursor, cursor_field, and default_cursor_field are all false-y, this is an invalid configuration.

Schema Mismatches​

Over time, it is possible for the catalog to become out of sync with the underlying data store it represents. The Protocol is design to be resilient to this. In should never fail due to a mismatch.

ScenarioOutcome
Stream exists in catalog but not in data storeWhen the source runs, it will not find the data for that stream. All other streams sync as usual.
Stream exists in data store but not in catalogWhen the source runs, it never looks for the data in the store related to that stream and thus does not emit it.
Field exists in catalog but not in data storeIf the column for a table is remove in the underlying data store the Source will not find it and will not replicate it. It should not cause a failure. The data simply will not be there.
Field exists in data store but not in catalogWhen the source runs, it never looks for the field in the store. It should not emit that field. If it does, it should be ignored downstream. The existence of an unknown field should not cause a failure.

In short, if the catalog is ever out of sync with the schema of the underlying data store, it should never block replication for data that is present.

State & Checkpointing​

Sources are able to emit state in order to allow checkpointing data replication. The goal is that given wherever a sync stops (whether this is due to all data available at the time being replicated or due to a failure), the next time the Source attempts to extract data it can pick up where it left off and not have to go back to the beginning.

This concept enables incremental syncs--syncs that only replicate data that is new since the previous sync.

State also enables Partial Success. In the case where during a sync there is a failure before all data has been extracted and committed, if all records up to a certain state are committed, then the next time the sync happens, it can start from that state as opposed to going back to the beginning. Partial Success is powerful, because especially in the case of high data volumes and long syncs, being able to pick up from wherever the failure occurred can costly re-syncing of data that has already been replicated.

The state for an actor is emitted as a black box by the Source. When emitted it is wrapped in the AirbyteStateMessage. The contents of the data field is what is passed to the Source on start up. It is up to the Source to interpret the state object. Nothing outside the Source can make any inference about the state of the object EXCEPT, if it is null, it can be concluded that there is no state and the Source will start at the beginning.

State & Source​

This section will step through how state is used to allow a Source to pick up where it left off. A Source takes state as an input. A Source should be able to take that input and use it to determine where it left off the last time. The contents of the Source is a black box to the Protocol. The Protocol provides an envelope for the Source to put its state in and then passes the state back in that envelope. The Protocol never needs to know anything about the contents of the state. Thus, the Source can track state however makes most sense to it.

Here is an example of the lifecycle of state in reference to the Source.

-- link to source image

In Sync 1, the Postgres Source receives null state as an input. Thus, when it queries data from the database, it starts at the beginning and returns all the records it finds. In addition, it emits state records that show track the high watermark of what records it has replicated. The Source has broad latitude to decide how frequently it will emit state records. In this implementation it emits a state message for each new day of the created_at it processes.

In Sync 2, the last state that was emitted from Sync 1 is passed into the Source. When the Source queries the data, it knows that it has already replicated records from 2022/01/02 and before, so it does not resend them. It just emits records after that date.

While this example, demonstrates a success case, we can see how this process helps in failure cases as well. Let's say that in Sync 1 after emitting the first state message and before emitting the record for Carl, the Source lost connectivity with Postgres due to a network blip and the Source Actor crashed. When Sync 2 runs, it will get the state record with 2022/01/01 instead, so it will replicate Carl and Drew, but it skips Alice and Bob. While in this toy example this procedure only saves replicating one record, in a production use case, being able to checkpoint regularly can save having to resend huge amounts of data due to transient issues.

State & the Whole Sync​

The previous section, for the sake of clarity, looked exclusively at the life cycle of state relative to the Source. In reality knowing that a record was emitted from the Source is NOT enough guarantee to know that we can skip sending the record in future syncs. For example, imagine the Source successfully emits the record, but the Destination fails. If we skip that record in the next sync, it means it never truly made it to its destination. This insight means, that a State should only ever be passed to a Source in the next run if it was both emitted from the Source and the Destination.

This image looks at two time points during an example sync. At T1 the Source has emitted 3 records and 2 state messages. If the Sync were to fail now, the next sync should start at the beginning because no records have been saved to the destination.

At T2, the Destination has received all records before the first state message and has emitted that that state message. By emitting that state message, the destination is confirming that all records in that state message have been committed. The diagram only shows the state being emitted because the destination does not emit record messages, only state messages. In addition, the Source has also emitted more records, including the record for Drew and another state message. If the sync were to fail at T2, then the next sync could start replicating records after Bob. Because the state records for Carl and Drew did not make it through to the destination, despite being emitted by the source, they have to be resent.

The normal success case (T3, not depicted) would be that all the records would move through the destination and the last state message that the Source emitted is then emitted by the Destination. The Source and Destination would both close STDOUT and exit 0 signal that they have emitted all records without failure.

-- link to source image

State Types​

In addition to allowing a Source to checkpoint data replication, the state object allows for the ability to configure and reset streams in isolation from each other. For example, if adding or removing a stream, it is possible to do so without affecting the state of any other stream in the Source.

There are 3 types of state: Stream, Global, and Legacy.

  • Stream represents Sources where there is complete isolation between stream states. In these cases, the state for each stream will be emitted in its own state message. In other words, if there are 3 streams replicated during a sync, the Source would emit at least 3 state message (1 per stream). The state of the Source is the sum of all the stream states.
  • Global represents Sources where this shared state across streams. In these cases each state message contains the whole state for the connection. The shared_state field is where any information that is shared across streams must go. The stream_states field contains a list of objects that contain a Stream Descriptor and the state information for that stream that is stream-specific. There are drawbacks to this state type, so it should only be used in cases where a shared state between streams is unavoidable.
  • Legacy exists for backwards compatibility. In this state type, the state object is totally a black box. The only inference tha can be drawn from the state object is that if it is null, then there is no state for the entire Source. All current legacy cases are being ported to stream or global. Once they are, it will be removed.

This table breaks down attributes of these state types.

StreamGlobalLegacy
Stream-Level Configuration / ResetXX
Stream-Level Replication IsolationX
Single state message describes full state for SourceXX
  • Stream-Level Configuration / Reset was mentioned above. The drawback of the old state struct was that it was not possible to configure or reset the state for a single stream without doing it for all of them. Thus, new state types support this, but the legacy one cannot.
  • Stream-Level Replication Isolation means that a Source could be run in parallel by splitting up its streams across running instances. This is only possible for Stream state types, because they are the only state type that can update its current state completely on a per-stream basis. This is one of the main drawbacks of Sources that use Global state; it is not possible to increase their throughput through parallelization.
  • Single state message describes full state for Source means that any state message contains the full state information for a Source. Stream does not meet this condition because each state message is scoped by stream. This means that in order to build a full picture of the state for the Source, the state messages for each configured stream must be gathered.

State Principles​

The following are principles Airbyte recommends Sources/Destinations adhere to with State. Airbyte enforces these principles via our CDK.

These principles are intended to produce simple overall system behavior, and move Airbyte towards a world of shorter-lived jobs. The goal is reliable data movement with minimal data loss windows on errors.

  1. New Sources must use per-stream/global State.

    Per-stream/Global state unlocks more granular State operations e.g. per-stream resets, per-stream parallelisation etc. No new Connectors should be created using Legacy state.

  2. Sources always emit State, regardless of sync mode.

    This simplifies how the Platform treats jobs and means all Syncs are resumable. This also enables checkpointing on full refreshes in the future. This rule does not appear to Sources that do not support cursors. However:

    1. If the source stream has no records, an empty state should still be emitted. This supports state-based counts/checksums. It is recommended for the emitted state to have unique and non-null content.
    2. If the stream is unsorted, and therefore non-resumable, it is recommended to still send a state message, even with bogus resumability, to indicate progress in the sync.

  3. Sources do not emit sequential duplicate States with interleaved records.

    Duplicate States make it challenging to debug state-related operations. E.g. Is this a duplicate or did we fail to properly update state? Is this a duplicate log? Sync will fail if this rule is violated.

  4. Sources should emit state whenever it is meaningful to resume a failed sync. Platform reserves the right to discard too frequent State emission per internal platform rules.

    Sources should strive to emit state as fast as it’s useful. Platform can discard this state if this leads to undesirable downstream behavior e.g. out of memory. This is fine as there is increasingly lower marginal value to emitting States at higher frequencies.

  5. Platform & Destinations treat state as a black box.

    Sources are the sole producer/consumer of a State messages’ contents. Precisely, this refers to the state fields within the various State messages. Modifying risks corrupting our data sync cursor, which is a strict no-no.

  6. Destinations return state in the order it was received.

    Order is used by the Platform to determine if a State message was dropped. Out-of-order State messages throw errors, as do skipped state messages. Every state message the destination recieved must be returned back to the platform, in order.

    Order-ness is determined by the type of State message. Per-stream state messages require order per-stream. Global state messages require global ordering.

Messages​

Common​

For forwards compatibility all messages should allow for unknown properties (in JSONSchema parlance that is additionalProperties: true).

Messages are structs emitted by actors.

StreamDescriptor​

A stream descriptor contains all information required to identify a Stream:

  • The name of the stream (required). It may not be null.
  • The namespace of the stream (optional). It may be null if the stream does not have an associated namespace, otherwise must be populated.
  • Any UTF-8 string value is valid for both name and namespace, including the empty string ("") value.

This is the new pattern for referring to a stream. As structs are updated, they are moved ot use this pattern. Structs that have not been updated still refer to streams by having top-level fields called stream_name and namespace.

StreamDescriptor:
  type: object
  additionalProperties: true
  required:
    - name
  properties:
    name:
      type: string
    namespace:
      type: string

AirbyteMessage​

The output of each method in the actor interface is wrapped in an AirbyteMessage. This struct is an envelope for the return value of any message in the described interface.

The envelope has a required type which described the type of the wrapped message. Based on the type only the field of that type will be populated. All other fields will be null.

AirbyteMessage:
  type: object
  additionalProperties: true
  required:
    - type
  properties:
    type:
      description: "Message type"
      type: string
      enum:
        - RECORD
        - STATE
        - LOG
        - SPEC
        - CONNECTION_STATUS
        - CATALOG
        - TRACE
    log:
      description: "log message: any kind of logging you want the platform to know about."
      "$ref": "#/definitions/AirbyteLogMessage"
    spec:
      "$ref": "#/definitions/ConnectorSpecification"
    connectionStatus:
      "$ref": "#/definitions/AirbyteConnectionStatus"
    catalog:
      description: "catalog message: the catalog"
      "$ref": "#/definitions/AirbyteCatalog"
    record:
      description: "record message: the record"
      "$ref": "#/definitions/AirbyteRecordMessage"
    state:
      description: "schema message: the state. Must be the last message produced. The platform uses this information"
      "$ref": "#/definitions/AirbyteStateMessage"
    trace:
      description: "trace message: a message to communicate information about the status and performance of a connector"
      "$ref": "#/definitions/AirbyteTraceMessage"

AirbyteRecordMessage​

The record message contains the actual data that is being replicated.

The namespace and stream fields are used to identify which stream the data is associated with. namespace can be null if the stream does not have an associated namespace. If it does, it must be populated.

The data contains the record data and must always be populated. It is a JSON blob.

The emitted_at field contains when the source extracted the record. It is a required field.

AirbyteRecordMessage:
  type: object
  additionalProperties: true
  required:
    - stream
    - data
    - emitted_at
  properties:
    namespace:
      description: "namespace the data is associated with"
      type: string
    stream:
      description: "stream the data is associated with"
      type: string
    data:
      description: "record data"
      type: object
      existingJavaType: com.fasterxml.jackson.databind.JsonNode
    emitted_at:
      description: "when the data was emitted from the source. epoch in millisecond."
      type: integer

AirbyteStateMessage​

The state message enables the Source to emit checkpoints while replicating data. These checkpoints mean that if replication fails before completion, the next sync is able to start from the last checkpoint instead of returning to the beginning of the previous sync. The details of this process are described in State & Checkpointing.

In the previous version of the protocol, the state object that the Source emitted was treated entirely as a black box. In the current version of protocol, Sources split up state by Stream. Within each Stream, the state is treated like a black box. The current version of the protocol is backwards compatible to the previous state message. The previous version is referred to as type LEGACY (if type is not set, it is assumed that the state message is LEGACY).

state_type is a required field. Only the field associated with that type we be populated. All others will be null. If the type is LEGACY and data is null, that means the state should be reset.

STREAM is the common way of constructing states and should be preferred wherever possible. In the STREAM case, the state for each stream is emitted in a separate message. This is described by the AirbyteStreamState struct. The stream_descriptor field is required to determine which stream a state is associated with. stream_state contains the black box state for a stream. If it is null, it means that the state for that stream should be reset.

In the GLOBAL case, the state for the whole Source is encapsulated in the message (see: AirbyteGlobalState). Within that message the state for individual streams is split. The GLOBAL case allows the author of a Source to share state across streams (shared_state). The contract is that if the state of the stream is set to null in stream_states then the next time the Source runs, it should treat that state as reset. This message should only be used in cases where there is a shared state across streams (e.g. CDC where the WAL log number is a global cursor), otherwise prefer STREAM.

AirbyteStateMessage:
  type: object
  additionalProperties: true
  properties:
    state_type:
      "$ref": "#/definitions/AirbyteStateType"
    stream:
      "$ref": "#/definitions/AirbyteStreamState"
    global:
      "$ref": "#/definitions/AirbyteGlobalState"
    data:
      description: "(Deprecated) the state data"
      type: object
      existingJavaType: com.fasterxml.jackson.databind.JsonNode
AirbyteStateType:
  type: string
  description: >
    The type of state the other fields represent.
    Is set to LEGACY, the state data should be read from the `data` field for backwards compatibility.
    If not set, assume the state object is type LEGACY.
    GLOBAL means that the state should be read from `global` and means that it represents the state for all the streams. It contains one shared
    state and individual stream states.
    PER_STREAM means that the state should be read from `stream`. The state present in this field correspond to the isolated state of the
    associated stream description.
  enum:
    - GLOBAL
    - STREAM
    - LEGACY
AirbyteStreamState:
  type: object
  additionalProperties: true
  required:
    - stream_descriptor
  properties:
    stream_descriptor:
      "$ref": "#/definitions/StreamDescriptor"
    stream_state:
      "$ref": "#/definitions/AirbyteStateBlob"
AirbyteGlobalState:
  type: object
  additionalProperties: true
  required:
    - stream_states
  properties:
    shared_state:
      "$ref": "#/definitions/AirbyteStateBlob"
    stream_states:
      type: array
      items:
        "$ref": "#/definitions/AirbyteStreamState"

AirbyteConnectionStatus Message​

This message reports whether an Actor was able to connect to its underlying data store with all the permissions it needs to succeed. The goal is that if a successful stat is returned, that the user should be confident that using that Actor will succeed. The depth of the verification is not specified in the protocol. More robust verification is preferred but going too deep can create undesired performance tradeoffs.

AirbyteConnectionStatus:
  description: Airbyte connection status
  type: object
  additionalProperties: true
  required:
    - status
  properties:
    status:
      type: string
      enum:
        - SUCCEEDED
        - FAILED
    message:
      type: string

ConnectorSpecification Message​

This message returns the ConnectorSpecification struct which is described in detail in Actor Specification

AirbyteCatalog Message​

This message returns the AirbyteCatalog struct which is described in detail in Catalog

AirbyteLogMessage​

Logs are helping for debugging an Actor. In order for a log emitted from an Actor be properly parsed it should be emitted as an AirbyteLogMessage wrapped in an AirbyteMessage.

The Airbyte implementation of the protocol does attempt to parse any data emitted from an Actor as a log, even if it is not properly wrapped in an AirbyteLogMessage. It attempts to treat any returned line that is not JSON or that is JSON but is not an AirbyteMessage as a log. This an implementation choice outside the boundaries of the strict protocol. The downside of this approach is that metadata about the log that would be captured in the AirbyteLogMessage is lost.

AirbyteLogMessage:
  type: object
  additionalProperties: true
  required:
    - level
    - message
  properties:
    level:
      description: "log level"
      type: string
      enum:
        - FATAL
        - ERROR
        - WARN
        - INFO
        - DEBUG
        - TRACE
    message:
      description: "log message"
      type: string
    stack_trace:
      description: "an optional stack trace if the log message corresponds to an exception"
      type: string

AirbyteTraceMessage​

The trace message allows an Actor to emit metadata about the runtime of the Actor, such as errors or estimates. This message is designed to grow to handle other use cases, including additonal performance metrics.

AirbyteTraceMessage:
  type: object
  additionalProperties: true
  required:
    - type
    - emitted_at
  properties:
    type:
      title: "trace type" # this title is required to avoid python codegen conflicts with the "type" parameter in AirbyteMessage. See https://github.com/airbytehq/airbyte/pull/12581
      description: "the type of trace message"
      type: string
      enum:
        - ERROR
        - ESTIMATE
    emitted_at:
      description: "the time in ms that the message was emitted"
      type: number
    error:
      description: "error trace message: the error object"
      "$ref": "#/definitions/AirbyteErrorTraceMessage"
    estimate:
      description: "Estimate trace message: a guess at how much data will be produced in this sync"
      "$ref": "#/definitions/AirbyteEstimateTraceMessage"
AirbyteErrorTraceMessage:
  type: object
  additionalProperties: true
  required:
    - message
  properties:
    message:
      description: A user-friendly message that indicates the cause of the error
      type: string
    internal_message:
      description: The internal error that caused the failure
      type: string
    stack_trace:
      description: The full stack trace of the error
      type: string
    failure_type:
      description: The type of error
      type: string
      enum:
        - system_error
        - config_error
AirbyteEstimateTraceMessage:
  type: object
  additionalProperties: true
  required:
    - name
    - type
  properties:
    name:
      description: The name of the stream
      type: string
    type:
      description: The type of estimate
      type: string
      enum:
        - STREAM
        - SYNC
    namespace:
      description: The namespace of the stream
      type: string
    row_estimate:
      description: The estimated number of rows to be emitted by this sync for this stream
      type: integer
    byte_estimate:
      description: The estimated number of bytes to be emitted by this sync for this stream
      type: integer

AirbyteErrorTraceMessage​

Error Trace Messages are used when a sync is about to fail and the connector can provide meaningful information to the orhcestrator or user about what to do next.

Of note, an internal_message might be an exception code, but an external_message is meant to be user-facing, e.g. "Your API Key is invalid".

Syncs can fail for multiple reasons, and therefore multiple AirbyteErrorTraceMessage can be sent from a connector.

AirbyteEstimateTraceMessage​

Estimate Trace Messages are used by connectors to inform the orchestrator about how much data they expect to move within the sync. This ise useful to present the user with estimates of the time remaining in the sync, or percentage complete. An example of this would be for every stream about to be synced from a databse to provde a COUNT (*) from {table_name} where updated_at > {state} to provide an estimate of the rows to be sent in this sync.

AirbyteEstimateTraceMessage should be emitted early in the sync to provide an early estimate of the sync's duration. Multiple AirbyteEstimateTraceMessages can be sent for the same stream, and an updated estimate will replace the previous value.

AirbyteControlMessage​

An AirbyteControlMessage is for connectors to signal to the Airbyte Platform or Orchestrator that an action with a side-effect should be taken. This means that the Orchestrator will likely be altering some stored data about the connector, connection, or sync.

AirbyteControlMessage:
  type: object
  additionalProperties: true
  required:
    - type
    - emitted_at
  properties:
    type:
      title: orchestrator type
      description: "the type of orchestrator message"
      type: string
      enum:
        - CONNECTOR_CONFIG
    emitted_at:
      description: "the time in ms that the message was emitted"
      type: number
    connectorConfig:
      description: "connector config orchestrator message: the updated config for the platform to store for this connector"
      "$ref": "#/definitions/AirbyteControlConnectorConfigMessage"

AirbyteControlConnectorConfigMessage​

AirbyteControlConnectorConfigMessage allows a connector to update its configuration in the middle of a sync. This is valuable for connectors with short-lived or single-use credentials.

Emitting this message signals to the orchestrator process that it should update its persistence layer, replacing the connector's current configuration with the config present in the .config field of the message.

The config in the AirbyteControlConnectorConfigMessage must conform to connector's specification's schema, and the orchestrator process is expected to validate these messages. If the output config does not conform to the specification's schema, the orchestrator process should raise an exception and terminate the sync.

AirbyteControlConnectorConfigMessage:
  type: object
  additionalProperties: true
  required:
    - config
  properties:
    config:
      description: "the config items from this connector's spec to update"
      type: object
      additionalProperties: true

For example, if the currently persisted config file is {"api_key": 123, start_date: "01-01-2022"} and the following AirbyteControlConnectorConfigMessage is output {type: ORCHESTRATOR, connectorConfig: {"config": {"api_key": 456}, "emitted_at": <current_time>}} then the persisted configuration is merged, and will become {"api_key": 456, start_date: "01-01-2022"}.

Acknowledgements​

We'd like to note that we were initially inspired by Singer.io's specification and would like to acknowledge that some of their design choices helped us bootstrap our project. We've since made a lot of modernizations to our protocol and specification, but don't want to forget the tools that helped us get started.

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