Chapter 1. Introduction to Service Registry

Service Registry is a datastore for sharing standard event schemas and API designs across API and event-driven architectures. You can use Service Registry to decouple the structure of your data from your client applications, and to share and manage your data types and API descriptions at runtime using a REST interface.

For example, client applications can dynamically push or pull the latest schema updates to or from Service Registry at runtime without needing to redeploy. Developer teams can query the registry for existing schemas required for services already deployed in production, and can register new schemas required for new services in development.

You can enable client applications to use schemas and API designs stored in Service Registry by specifying the registry URL in your client application code. For example, the registry can store schemas used to serialize and deserialize messages, which can then be referenced from your client applications to ensure that the messages that they send and receive are compatible with those schemas.

Using Service Registry to decouple your data structure from your applications reduces costs by decreasing overall message size, and creates efficiencies by increasing consistent reuse of schemas and API designs across your organization. Service Registry provides a web console to make it easy for developers and administrators to manage registry content.

In addition, you can configure optional rules to govern the evolution of your registry content. For example, these include rules to ensure that uploaded content is syntactically and semantically valid, or is backwards and forwards compatible with other versions. Any configured rules must pass before new versions can be uploaded to the registry, which ensures that time is not wasted on invalid or incompatible schemas or API designs.

Service Registry is based on the Apicurio Registry open source community project. For details, see https://github.com/apicurio/apicurio-registry.

Service Registry capabilities

The items stored in Service Registry, such as event schemas and API specifications, are known as registry artifacts. The following shows an example of an Apache Avro schema artifact in JSON format for a simple share price application:

{
   "type": "record",
   "name": "price",
   "namespace": "com.example",
   "fields": [
       {
           "name": "symbol",
           "type": "string"
       },
       {
           "name": "price",
           "type": "string"
       }
   ]
}

When a schema or API contract is added as an artifact in the registry, client applications can then use that schema or API contract to validate that client messages conform to the correct data structure at runtime.

Service Registry supports a wide range of message payload formats for standard event schemas and API specifications. For example, supported formats include Apache Avro, Google protocol buffers, GraphQL, AsyncAPI, OpenAPI, and others. For more details, see Chapter 14, Service Registry artifact reference.

Service Registry provides the following underlying storage implementations for registry artifacts:

You can use the Service Registry web console to browse and search the artifacts stored in the registry, and to upload new artifacts and artifact versions. You can search for artifacts by label, name, and description. You can also view an artifact’s content, view all of its available versions, or download an artifact file locally.

You can also use the Service Registry web console to configure optional rules for registry content, both globally and for each artifact. These optional rules for content validation and compatibility are applied when new artifacts or artifact versions are uploaded to the registry. For more details, see Chapter 14, Service Registry artifact reference.

Figure 1.1. Service Registry web console

The Service Registry web console is available from the main endpoint of your Service Registry deployment, for example, on http://MY-REGISTRY-URL/ui.

Kafka producer applications can use serializers to encode messages that conform to a specific event schema. Kafka consumer applications can then use deserializers to validate that messages have been serialized using the correct schema, based on a specific schema ID.

Figure 1.2. Service Registry and Kafka client serializer/deserializer architecture

Service Registry provides Kafka client serializers/deserializers (Serdes) to validate the following message types at runtime:

The Service Registry Maven repository and source code distributions include the Kafka serializer/deserializer implementations for these message types, which Kafka client developers can use to integrate with the registry. These implementations include custom io.apicurio.registry.utils.serde Java classes for each supported message type, which client applications can use to pull schemas from the registry at runtime for validation.

You can use Service Registry with Apache Kafka Connect to stream data between Kafka and external systems. Using Kafka Connect, you can define connectors for different systems to move large volumes of data into and out of Kafka-based systems.

Figure 1.3. Service Registry and Kafka Connect architecture

Service Registry provides the following features for Kafka Connect:

You can use the Avro and JSON Schema converters to map Kafka Connect schemas into Avro or JSON schemas. Those schemas can then serialize message keys and values into the compact Avro binary format or human-readable JSON format. The converted JSON is also less verbose because the messages do not contain the schema information, only the schema ID.

Service Registry can manage and track the Avro and JSON schemas used in the Kafka topics. Because the schemas are stored in Service Registry and decoupled from the message content, each message must only include a tiny schema identifier. For an I/O bound system like Kafka, this means more total throughput for producers and consumers.

The Avro and JSON Schema serializers and deserializers (Serdes) provided by Service Registry are also used by Kafka producers and consumers in this use case. Kafka consumer applications that you write to consume change events can use the Avro or JSON Serdes to deserialize these change events. You can install these Serdes into any Kafka-based system and use them along with Kafka Connect, or with Kafka Connect-based systems such as Debezium and Camel Kafka Connector.

Service Registry provides an open source demonstration of Apache Avro serialization/deserialization with storage in Apache Kafka Streams. This example shows how the serializer/deserializer obtains the Avro schema from the registry at runtime and uses it to serialize and deserialize Kafka messages. For more details, see https://github.com/Apicurio/apicurio-registry-demo.

Service Registry also provides the following example applications:

For more details, see https://github.com/Apicurio/apicurio-registry-examples