Hydra

The Hydra platform provides a streamlined data streaming experience by abstracting away the underlying implementation, instead providing users a simple REST API.

Hydra Modules

Common

A set of common util-based classes meant to be shared across the entire Hydra ecosystem, including hydra-spark and dispatch modules.

Core

Core, shared traits and classes that define both the ingestion and transport protocols in Hydra. This module is a dependency to any ingestor or transport implementation.

This also includes Avro schema resolution, validation, and management.

Ingest

The ingestion implementation, including HTTP endpoints, actors, communication protocols, registration of ingestors, and a lot of other stuff.

Kafka

A Transport implementation that replicates messages into Kafka.

Building Hydra

Hydra is built using SBT. To build Hydra, run:

sbt clean compile

Docker

Services needed to run Hydra

• Kafka 2.0.0
• Confluent Schema Registry 5.0.0
• Zookeeper (3.x +)

This documentation walks through setting up the core basic components of Hydra.

Create a VirtualBox instance

docker-machine create --driver virtualbox --virtualbox-memory 6000 hydra

Configure Terminal to attach to the new machine

docker-machine env hydra

Create a Docker network

docker network create hydra

Start Zookeeper

Hydra uses Zookeeper as a coordination service to automate bootstrapping and joining a cluster.

It is also used by Kafka and the Schema Registry.

Since all services depend on Zookeeper being up, so we will start that first. It is not always needed to do this, but doing so avoids race conditions tht may happen across the different containers.

docker-compose up -d zookeeper

Start Hydra

docker-compose up hydra

You can also start each service separately.

That should do it!

Checking if Hydra is Running

You can test Hydra has started by going to this resource:

http://localhost:8088/health

You should see something like:

{
  "BuildInfo": {
    "builtAtMillis": "1639518050466",
    "name": "hydra-ingest",
    "scalaVersion": "2.12.11",
    "version": "0.11.3.979",
    "sbtVersion": "1.3.13",
    "builtAtString": "2021-12-14 21:40:50.466"
  },
  "ConsumerGroupisActive": {
    "ConsumerGroupName": "v2MetadataConsumer",
    "State": true
  }
}

Available Endpoints

Container Metadata

Path	HTTP Method	Description
/health	GET	A summary overview of the overall health of the system. Includes health checks for Kafka.
/metrics	GET	A collection of JVM-related memory and thread management metrics, including deadlocked threads, garbage collection run times, etc.

Schema Endpoints

Path	HTTP Method	Description
/schemas	GET	Returns a list of all schemas managed by Hydra.
/schemas/[NAME]	GET	Returns information for the latest version of a schema.
/schemas/[NAME]?schema	GET	Returns only the JSON for the latest schema.
/schemas/[NAME]/versions/	GET	Returns all versions for a schema.
/schemas/[NAME/versions/[VERSION]	GET	Returns metadata for a specific version of a schema
/schemas	POST	Registers a new schema with the registry. Use this for both new and existing schemas; for existing schemas, compatibility will be checked prior to registration.

Topics Endpoints

Path	HTTP Method	Description
/v2/topics	GET	A list of all the registered topics currently managed by Hydra.
/v2/topics/[NAME]	GET	Get the current schema for requested topic.
/v2/topics/[NAME]	POST	Create or update custom topics. Also registers key and value schemas in Schema Registry if applicable.
/v2/topics/[NAME]	DELETE	Delete topics. Requires authentication.

Records Endpoints

Path	HTTP Method	Description
/v2/topics/[NAME]/records	POST	Creates a new record in the specified topic.

How to Train Your Hydra

"If you want to make a Kafka topic from scratch, you must first invent the universe." -Carl Sagan

Create & Register a Topic

We are using this topic to test:

{
  "streamType": "Entity",
  "deprecated": false,
  "dataClassification": "InternalUseOnly",
  "contact": {
    "email": "john.doe@email.com"
  },
  "createdDate": "2022-01-25T12:00:00Z",
  "notes": "Here are some notes.",
  "parentSubjects": [],
  "teamName": "team-john-doe",
  "schemas": {
    "key": {
      "type": "record",
      "name": "key",
      "namespace": "",
      "fields": [
        {
          "name": "id",
          "type": {
            "type":"string",
            "logicalType":"uuid"
          },
          "doc":"This is a doc field."
        }
      ]
    },
    "value": {
      "type": "record",
      "name": "val",
      "namespace": "dvs.data_platform.dvs_sandbox",
      "fields": [
        {
          "name": "myValue",
          "type": "string",
          "doc":"It is my value."
        }
      ]
    }
  }
}

Post it to Hydra

curl -X POST localhost:8088/topics/tech.my-first-topic -d '{
  "streamType": "Entity",
  "deprecated": false,
  "dataClassification": "InternalUseOnly",
  "contact": {
    "email": "john.doe@email.com"
  },
  "createdDate": "2022-01-25T12:00:00Z",
  "notes": "Here are some notes.",
  "parentSubjects": [],
  "teamName": "team-john-doe",
  "schemas": {
    "key": {
      "type": "record",
      "name": "Test2",
      "namespace": "",
      "fields": [
        {
          "name": "id",
          "type": {
            "type":"string",
            "logicalType":"uuid"
          },
          "doc":"This is a doc field."
        }
      ]
    },
    "value": {
      "type": "record",
      "name": "Test2",
      "namespace": "dvs.data_platform.dvs_sandbox",
      "fields": [
        {
          "name": "myValue",
          "type": "string",
          "doc":"It is my value."
        }
      ]
    }
  }
}'

You should see something like this:

OK

Feeding Your Hydra (with HTTP)

 curl -X POST -d '{"key": {"id":"7db11b7a-4560-4a86-b00b-6f380bfb1564"}, "value":{"myValue":"someValue"}}' -H 'Content-Type: application/json'  'http://localhost:8088/v2/topics/tech.my-first-topic/records'

A sample Hydra response is:

{"offset":0,"partition":6}

Message Validation

Hydra validates payloads against the underlying schema. For instance:

curl -X POST -d '{"key": {"id":"123"}, "value":{"myValue":"someValue"}}' -H 'Content-Type: application/json'  'http://localhost:8088/v2/topics/tech.my-first-topic/records'

Should return:

hydra.avro.convert.StringToGenericRecord$InvalidLogicalTypeError: Invalid logical type. 
Expected UUID but received 123 
[http://schema-registry:8081/subjects/tech.my-first-topic-key/versions/latest/schema]

##But what about v1?

You may have noticed that the JSON above uses "/v2" endpoints. Most /v2 endpoints have /v1 counterparts, but we highly recommend using /v2 as /v1 endpoints are deprecated. If you need to use "/v1" endpoints, simply remove the "/v2" segment.

Online Documentation

We used to highly recommend checking out the project documentation here, but then we forgot about it for two years. We might get around to updating it in the future.

There you can find the "latest" documentation about the Hydra project, including examples, API endpoints, and a lot more info on how to get started.

This README file only contains basic definitions and set up instructions.

Contribution and Development

Contributions via Github Pull Request are welcome.

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Contact

Try using the gitter chat link above!

License

Apache 2.0, see LICENSE.md