druid/docs/development/extensions-core/avro.md

id	title
avro	Apache Avro

This Apache Druid (incubating) extension enables Druid to ingest and understand the Apache Avro data format. Make sure to include druid-avro-extensions as an extension.

Avro Stream Parser

This is for streaming/realtime ingestion.

Field	Type	Description	Required
type	String	This should say avro_stream.	no
avroBytesDecoder	JSON Object	Specifies how to decode bytes to Avro record.	yes
parseSpec	JSON Object	Specifies the timestamp and dimensions of the data. Should be an "avro" parseSpec.	yes

An Avro parseSpec can contain a flattenSpec using either the "root" or "path" field types, which can be used to read nested Avro records. The "jq" field type is not currently supported for Avro.

For example, using Avro stream parser with schema repo Avro bytes decoder:

"parser" : {
  "type" : "avro_stream",
  "avroBytesDecoder" : {
    "type" : "schema_repo",
    "subjectAndIdConverter" : {
      "type" : "avro_1124",
      "topic" : "${YOUR_TOPIC}"
    },
    "schemaRepository" : {
      "type" : "avro_1124_rest_client",
      "url" : "${YOUR_SCHEMA_REPO_END_POINT}",
    }
  },
  "parseSpec" : {
    "format": "avro",
    "timestampSpec": <standard timestampSpec>,
    "dimensionsSpec": <standard dimensionsSpec>,
    "flattenSpec": <optional>
  }
}

Avro Bytes Decoder

If type is not included, the avroBytesDecoder defaults to schema_repo.

Inline Schema Based Avro Bytes Decoder

The "schema_inline" decoder reads Avro records using a fixed schema and does not support schema migration. If you may need to migrate schemas in the future, consider one of the other decoders, all of which use a message header that allows the parser to identify the proper Avro schema for reading records.

This decoder can be used if all the input events can be read using the same schema. In that case schema can be specified in the input task JSON itself as described below.

...
"avroBytesDecoder": {
  "type": "schema_inline",
  "schema": {
    //your schema goes here, for example
    "namespace": "org.apache.druid.data",
    "name": "User",
    "type": "record",
    "fields": [
      { "name": "FullName", "type": "string" },
      { "name": "Country", "type": "string" }
    ]
  }
}
...

Multiple Inline Schemas Based Avro Bytes Decoder

This decoder can be used if different input events can have different read schema. In that case schema can be specified in the input task JSON itself as described below.

...
"avroBytesDecoder": {
  "type": "multiple_schemas_inline",
  "schemas": {
    //your id -> schema map goes here, for example
    "1": {
      "namespace": "org.apache.druid.data",
      "name": "User",
      "type": "record",
      "fields": [
        { "name": "FullName", "type": "string" },
        { "name": "Country", "type": "string" }
      ]
    },
    "2": {
      "namespace": "org.apache.druid.otherdata",
      "name": "UserIdentity",
      "type": "record",
      "fields": [
        { "name": "Name", "type": "string" },
        { "name": "Location", "type": "string" }
      ]
    },
    ...
    ...
  }
}
...

Note that it is essentially a map of integer schema ID to avro schema object. This parser assumes that record has following format. first 1 byte is version and must always be 1. next 4 bytes are integer schema ID serialized using big-endian byte order. remaining bytes contain serialized avro message.

SchemaRepo Based Avro Bytes Decoder

This Avro bytes decoder first extract subject and id from input message bytes, then use them to lookup the Avro schema with which to decode Avro record from bytes. Details can be found in schema repo and AVRO-1124. You will need an http service like schema repo to hold the avro schema. Towards schema registration on the message producer side, you can refer to org.apache.druid.data.input.AvroStreamInputRowParserTest#testParse().

Field	Type	Description	Required
type	String	This should say schema_repo.	no
subjectAndIdConverter	JSON Object	Specifies the how to extract subject and id from message bytes.	yes
schemaRepository	JSON Object	Specifies the how to lookup Avro schema from subject and id.	yes

Avro-1124 Subject And Id Converter

This section describes the format of the subjectAndIdConverter object for the schema_repo Avro bytes decoder.

Field	Type	Description	Required
type	String	This should say avro_1124.	no
topic	String	Specifies the topic of your Kafka stream.	yes

Avro-1124 Schema Repository

This section describes the format of the schemaRepository object for the schema_repo Avro bytes decoder.

Field	Type	Description	Required
type	String	This should say avro_1124_rest_client.	no
url	String	Specifies the endpoint url of your Avro-1124 schema repository.	yes

Confluent Schema Registry-based Avro Bytes Decoder

This Avro bytes decoder first extract unique id from input message bytes, then use them it lookup in the Schema Registry for the related schema, with which to decode Avro record from bytes. Details can be found in Schema Registry documentation and repository.

Field	Type	Description	Required
type	String	This should say schema_registry.	no
url	String	Specifies the url endpoint of the Schema Registry.	yes
capacity	Integer	Specifies the max size of the cache (default == Integer.MAX_VALUE).	no

...
"avroBytesDecoder" : {
   "type" : "schema_registry",
   "url" : <schema-registry-url>
}
...

Avro Hadoop Parser

This is for batch ingestion using the HadoopDruidIndexer. The inputFormat of inputSpec in ioConfig must be set to "org.apache.druid.data.input.avro.AvroValueInputFormat". You may want to set Avro reader's schema in jobProperties in tuningConfig, e.g.: "avro.schema.input.value.path": "/path/to/your/schema.avsc" or "avro.schema.input.value": "your_schema_JSON_object", if reader's schema is not set, the schema in Avro object container file will be used, see Avro specification. Make sure to include "org.apache.druid.extensions:druid-avro-extensions" as an extension.

Field	Type	Description	Required
type	String	This should say avro_hadoop.	no
parseSpec	JSON Object	Specifies the timestamp and dimensions of the data. Should be an "avro" parseSpec.	yes

An Avro parseSpec can contain a flattenSpec using either the "root" or "path" field types, which can be used to read nested Avro records. The "jq" field type is not currently supported for Avro.

For example, using Avro Hadoop parser with custom reader's schema file:

{
  "type" : "index_hadoop",
  "spec" : {
    "dataSchema" : {
      "dataSource" : "",
      "parser" : {
        "type" : "avro_hadoop",
        "parseSpec" : {
          "format": "avro",
          "timestampSpec": <standard timestampSpec>,
          "dimensionsSpec": <standard dimensionsSpec>,
          "flattenSpec": <optional>
        }
      }
    },
    "ioConfig" : {
      "type" : "hadoop",
      "inputSpec" : {
        "type" : "static",
        "inputFormat": "org.apache.druid.data.input.avro.AvroValueInputFormat",
        "paths" : ""
      }
    },
    "tuningConfig" : {
       "jobProperties" : {
          "avro.schema.input.value.path" : "/path/to/my/schema.avsc"
      }
    }
  }
}