Schema Registry Maven Plugin

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A Maven plugin for Confluent Schema Registry is available to help throughout the development process, with configuration options as listed below.

Tip

There is no official out-of-the-box Gradle plugin available for Schema Registry. However, you can reference any of these plugins in your Maven pom.xml (Project Object Model file):

configs for all goals

Starting with Confluent Platform 7.0.0, the configs option is available for the Schema Registry Maven plugin for all goals. You can use configs to add any valid configuration to the CachedSchemaRegistryClient.

The syntax details are:

configs

  • Type: Map<String, String>
  • Required: false

For example, to set up SSL for the Maven plugin, specify the keystore/truststore location by adding the following configuration to the plugin:

<configuration>
   <configs>
     <schema.registry.ssl.keystore.location>path-to-keystore.jks</schema.registry.ssl.keystore.location>
     <schema.registry.ssl.keystore.password>password</schema.registry.ssl.keystore.password>
     <schema.registry.ssl.truststore.location>path-to-truststore.jks</schema.registry.ssl.truststore.location>
     <schema.registry.ssl.truststore.password>password</schema.registry.ssl.truststore.password>
    </configs>
</configuration>

Note that the schema.registry. prefix is needed, just like other Schema Registry client configurations for HTTPS.

schema-registry:download

The download goal is used to pull down schemas from a Schema Registry server. This plugin is used to download schemas for the requested subjects and write them to a folder on the local file system. If the versions array is empty, then the latest schemas are downloaded for all subjects. If the array is populated, its length must match the length of subjectPatterns array. This allows you to compare a new schema against a specific schema and to get older versions.

Tip

In Confluent Platform version 7.2.0-0 and later, you can specify a version to download, which better supports schema-registry:test-local-compatibility. Previous to Confluent Platform 7.2.0-0, you could only download the latest version.

schemaRegistryUrls

Schema Registry URLs to connect to.

  • Type: String[]
  • Required: true
userInfoConfig

User credentials for connecting to Schema Registry, of the form user:password. This is required if connecting to Confluent Cloud Schema Registry.

  • Type: String[]
  • Required: false
  • Default: null
outputDirectory

Output directory to write the schemas to.

  • Type: File
  • Required: true
schemaExtension

The file extension to use for the output file name. This must begin with a . character.

  • Type: File
  • Required: false
  • Default: .avsc
subjectPatterns

The subject patterns to download. This is a list of regular expressions. Patterns must match the entire subject name.

  • Type: String[]
  • Required: true

Example 1: Download the latest version of a schema

The following code uses the plugin to download the latest version of schemas with the subject pattern ^TestSubject000-(key|value)$ :

<plugin>
    <groupId>io.confluent</groupId>
    <artifactId>kafka-schema-registry-maven-plugin</artifactId>
    <version>7.2.12</version>
    <configuration>
        <schemaRegistryUrls>
            <param>http://192.168.99.100:8081</param>
        </schemaRegistryUrls>
        <outputDirectory>src/main/avro</outputDirectory>
        <subjectPatterns>
            <param>^TestSubject000-(key|value)$</param>
        </subjectPatterns>
    </configuration>
</plugin>

Example 2: Specify a schema version to download

The following code uses the plugin to download version 1 of schemas with the subject pattern ^topic1-(key|value)$, and the latest version of schemas with the subject pattern ^topic2-(key|value)$:

<plugin>
  <groupId>io.confluent</groupId>
  <artifactId>kafka-schema-registry-maven-plugin</artifactId>
  <version>7.2.12</version>
  <configuration>
      <schemaRegistryUrls>
          <param>http://127.0.0.1:8081</param>
      </schemaRegistryUrls>
      <outputDirectory>outputDir/target/</outputDirectory>
      <subjectPatterns>
          <param>^topic1-(key|value)$</param>
          <param>^topic2-(key|value)$</param>
      </subjectPatterns>
      <versions>
          <param>1</param>
          <param>latest</param>
      </versions>
  </configuration>
</plugin>

schema-registry:set-compatibility

The goal, schema-registry:set-compatibility, is available in Confluent Platform version 7.2.0-0 and later.

This goal is used to update the configuration of a subject or at a global level directly from the plugin. This enables you to change the compatibility levels with evolving schemas, and centralize your subject and schema management.

schemaRegistryUrls

Schema Registry URLs to connect to.

  • Type: String[]
  • Required: true
compatibilityLevels

Map of subjects and the compatibility types to be set in them, respectively.

  • Type: Map<String,String> (Subject,CompatibilityLevel)
  • Required: true

If subject is NULL or __GLOBAL, then the Global level configuration is updated. If CompatibilityLevel is NULL, then the configuration is deleted.

The following example uses the plugin to set the compatibility of the subject order to BACKWARD, product to FORWARD_TRANSITIVE, deleting the compatibility of customer and changing the Global compatibility to BACKWARD_TRANSITIVE:

<plugin>
  <groupId>io.confluent</groupId>
  <artifactId>kafka-schema-registry-maven-plugin</artifactId>
  <version>7.2.12</version>
  <configuration>
        <schemaRegistryUrls>
            <param>http://192.168.99.100:8081</param>
        </schemaRegistryUrls>
        <compatibilityLevels>
            <order>BACKWARD</order>
            <product>FORWARD_TRANSITIVE</product>
            <customer>null</customer>
            <__GLOBAL>BACKWARD_TRANSITIVE</__GLOBAL>
        </compatibilityLevels>
    </configuration>
</plugin>

Example Usage

Example usage of schema-registry:test-compatibility:

schema-registry:test-local-compatibility

This goal, available in Confluent Platform version 7.2.0-0 and later, tests compatibility of a local schema with other existing local schemas during development and testing phases.

Before the addition of schema-registry:test-local-compatibility, if you wanted to check compatibility of a new schema you had to connect to the Schema Registry. This meant registering all the schemas for which you want to perform compatibility checks, resulting in a reduction in available free schemas. This new goal solves that problem and supports quick, efficient compatibility testing of local schemas as appropriate for development phases.

Tip

For examples of testing schema compatibility using GitHub Actions, see the Workflows and Examples provided below, and the kafka-github-actions demo repo.

schemas

Map of schema and location of schemas for which compatibility test is performed

  • Type: Map<String, File>
  • Required: true
previousSchemaPaths

Map of schema and location of previous schemas. The compatibility test is performedfor a schema against the schemas in previousSchemaPaths. The location can be a directory or file name. If it is a directory name, all files inside folder are added. Subdirectories are ignored.

  • Type: Map<String, File>
  • Required: true
compatibilityLevels

Map of schema and the compatibility type for which check is performed. CompatibilityLevel is of type enum (one of NONE, BACKWARD, BACKWARD_TRANSITIVE, FORWARD, FORWARD_TRANSITIVE, FULL, or FULL_TRANSITIVE) For compatibility level BACKWARD, FORWARD, or FULL, exactly one previousSchema is expected per schema.

  • Type: Map<String, CompatibilityLevel>
  • Required: true
schemaTypes

String that specifies the schema type.

  • Type: Map<String, String> (one of AVRO (default), JSON, PROTOBUF)
  • Required: false
  • Default: AVRO

The following example uses the plugin to configure three subjects (order, product, and customer) using schema type: AVRO

<configuration>
        <schemas>
            <order>src/main/avro/order.avsc</order>
            <product>src/main/avro/product.avsc</product>
            <customer>src/main/avro/customer.avsc</customer>
        </schemas>
        <schemaTypes>
            <order>AVRO</order>
            <product>AVRO</product>
            <customer>AVRO</customer>
        </schemaTypes>
        <compatibilityLevels>
            <order>BACKWARD</order>
            <product>FORWARD</product>
            <customer>NONE</customer>
        </compatibilityLevels>
        <previousSchemaPaths>
            <order>src/main/avro/order.avsc</order>
            <product>src/main/avro/products/</product>
            <customer>src/main/avro/customer.avsc</customer>
        </previousSchemaPaths>
</configuration>

schema-registry:test-compatibility

This goal is used to read schemas from the local file system and test them for compatibility against the Schema Registry server(s). This goal can be used in a continuous integration pipeline to ensure that schemas in the project are compatible with the schemas in another environment.

Tip

For examples of testing schema compatibility using GitHub Actions, see the Workflows and Examples provided below, and the kafka-github-actions demo repo.

schemaRegistryUrls

Schema Registry URLs to connect to.

  • Type: String[]
  • Required: true
userInfoConfig

User credentials for connecting to Schema Registry, of the form user:password. This is required if connecting to Confluent Cloud Schema Registry.

  • Type: String[]
  • Required: false
  • Default: null
subjects

Map containing subject to schema path of the subjects to be registered.

  • Type: Map<String, File>
  • Required: true

Tip

Starting with Confluent Platform 5.5.5, you can specify a slash /, and other special characters, in a subject name. To do so, first URL-encode the subject name, and then replace non-valid characters in the output. For example, if you have a subject name such as path/to/my.proto, the URL encoding would produce something like `%2Fpath%2Fto%2Fmy.proto`, which you can then revise by replacing % with _x as follows: _x2Fpath_x2Fto_x2Fmy.proto (because % is not valid in an XML name). The reasoning behind this is that the Maven plugin requires subject names be specified as XML elements, but some characters, like slashes, are not valid characters in an XML name. You might want to use slashes to register a Protobuf schema that is referenced by another schema, such as /path/to/my.proto for the subject. This workaround enables you to do that.

schemaTypes

String that specifies the schema type.

  • Type: String (one of AVRO (default), JSON, PROTOBUF)
  • Required: false
  • Default: AVRO
references

Map containing a reference name and a subject.

  • Type: Map<String, Reference[]>
  • Required: false
verbose

Include in the output the reason the schema fails the compatibility test, in cases where it fails.

  • Type: Boolean
  • Required: false
  • Default: true

The following example uses the plugin to configure three subjects (order, product, and customer) using schema type: AVRO

<plugin>
    <groupId>io.confluent</groupId>
    <artifactId>kafka-schema-registry-maven-plugin</artifactId>
    <version>7.2.12</version>
    <configuration>
        <schemaRegistryUrls>
            <param>http://192.168.99.100:8081</param>
        </schemaRegistryUrls>
        <subjects>
            <order>src/main/avro/order.avsc</order>
            <product>src/main/avro/product.avsc</product>
            <customer>src/main/avro/customer.avsc</customer>
        </subjects>
        <schemaTypes>
            <order>AVRO</order>
            <product>AVRO</product>
            <customer>AVRO</customer>
        </schemaTypes>
        <references>
            <order>
              <reference>
                  <name>com.acme.Product</name>
                  <subject>product</subject>
              </reference>
              <reference>
                  <name>com.acme.Customer</name>
                  <subject>customer</subject>
              </reference>
            </order>
        </references>
    </configuration>
    <goals>
        <goal>test-compatibility</goal>
    </goals>
</plugin>

Example Usage

Example usage of schema-registry:test-compatibility:

schema-registry:validate

This goal is used to read schemas from the local file system and validate them locally, before registering them. If you find syntax errors, you can examine and correct them before submitting schemas to Schema Registry with schema-registry:register.

schemaRegistryUrls

Schema Registry URLs to connect to.

  • Type: String[]
  • Required: true
userInfoConfig

User credentials for connecting to Schema Registry, of the form user:password. This is required if connecting to Confluent Cloud Schema Registry.

  • Type: String[]
  • Required: false
  • Default: null
subjects

Map containing subject to schema path of the subjects to be registered.

  • Type: Map<String, File>
  • Required: true
schemaTypes

String that specifies the schema type.

  • Type: String (one of AVRO (default), JSON, PROTOBUF)
  • Required: false
  • Default: AVRO
references

Map containing a reference name and a subject.

  • Type: Map<String, Reference[]>
  • Required: false

schema-registry:register

This goal is used to read schemas from the local file system and register them on the target Schema Registry server(s). This goal can be used in a continuous deployment pipeline to push schemas to a new environment.

schemaRegistryUrls

Schema Registry URLs to connect to.

  • Type: String[]
  • Required: true
userInfoConfig

User credentials for connecting to Schema Registry, of the form user:password. This is required if connecting to Confluent Cloud Schema Registry.

  • Type: String[]
  • Required: false
  • Default: null
subjects

Map containing subject to schema path of the subjects to be registered.

  • Type: Map<String, File>
  • Required: true
schemaTypes

String that specifies the schema type.

  • Type: String (one of AVRO (default), JSON, PROTOBUF)
  • Required: false
  • Default: AVRO
normalizeSchemas

Normalizes schemas based on semantic equivalence during registration or lookup. To learn more, see Schema Normalization in Formats, Serializers, and Deserializers.

  • Type: Boolean
  • Required: false
  • Default: false
references

Map containing a reference name and a subject.

  • Type: Map<String, Reference[]>
  • Required: false

The following example uses the plugin to configure three subjects (order, product, and customer) using schema type: AVRO

<plugin>
    <groupId>io.confluent</groupId>
    <artifactId>kafka-schema-registry-maven-plugin</artifactId>
    <version>7.2.12</version>
    <configuration>
        <schemaRegistryUrls>
            <param>http://192.168.99.100:8081</param>
        </schemaRegistryUrls>
        <subjects>
            <order>src/main/avro/order.avsc</order>
            <product>src/main/avro/product.avsc</product>
            <customer>src/main/avro/customer.avsc</customer>
        </subjects>
        <schemaTypes>
            <order>AVRO</order>
            <product>AVRO</product>
            <customer>AVRO</customer>
        </schemaTypes>
        <references>
            <order>
              <reference>
                  <name>com.acme.Product</name>
                  <subject>product</subject>
              </reference>
              <reference>
                  <name>com.acme.Customer</name>
                  <subject>customer</subject>
              </reference>
            </order>
        </references>
    </configuration>
    <goals>
        <goal>register</goal>
    </goals>
</plugin>

Workflows and Examples

You can integrate Maven Plugin goals with GitHub Actions into a continuous integration/continuous deployment (CI/CD) pipleline to manage schemas on Schema Registry. A general example for developing and validating an Apache Kafka® client application with a Python producer and consumer is provided in the kafka-github-actions demo repo.

Here is an alternative sample pom.xml with project configurations for more detailed validate and register steps.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.confluent</groupId>
    <artifactId>GitHub-Actions-Demo</artifactId>
    <version>1.0</version>

<pluginRepositories>
    <pluginRepository>
        <id>confluent</id>
        <url>https://packages.confluent.io/maven/</url>
    </pluginRepository>
</pluginRepositories>

    <properties>
        <schemaRegistryUrl><$CONFLUENT_SCHEMA_REGISTRY_URL></schemaRegistryUrl>
        <schemaRegistryBasicAuthUserInfo>
            <$CONFLUENT_BASIC_AUTH_USER_INFO>
        </schemaRegistryBasicAuthUserInfo>
        <confluent.version>7.2.12</confluent.version>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>io.confluent</groupId>
                <artifactId>kafka-schema-registry-maven-plugin</artifactId>
                <version>${confluent.version}</version>
                <configuration>
                    <schemaRegistryUrls>
                        <param>${schemaRegistryUrl}</param>
                    </schemaRegistryUrls>
                    <userInfoConfig>${schemaRegistryBasicAuthUserInfo}</userInfoConfig>
                </configuration>
                <executions>

                    <execution>
                        <id>validate</id>
                        <phase>validate</phase>
                        <goals>
                            <goal>validate</goal>
                        </goals>
                        <configuration>
                            <subjects>
                                <Orders-value>src/main/resources/order.avsc</Orders-value>
                                <Flights-value>src/main/resources/flight.proto</Flights-value>
                            </subjects>
                            <schemaTypes>
                                <Flights-value>PROTOBUF</Flights-value>
                            </schemaTypes>

                        </configuration>
                    </execution>

                    <execution>
                        <id>set-compatibility</id>
                        <phase>validate</phase>
                        <goals>
                            <goal>set-compatibility</goal>
                        </goals>
                        <configuration>
                            <compatibilityLevels>
                                <Orders-value>FORWARD_TRANSITIVE</Orders-value>
                                <Flights-value>FORWARD_TRANSITIVE</Flights-value>
                            </compatibilityLevels>
                        </configuration>
                    </execution>


                    <execution>
                        <id>test-local</id>
                        <phase>validate</phase>
                        <goals>
                            <goal>test-local-compatibility</goal>
                        </goals>
                        <configuration>
                            <schemas>
                                <order>src/main/resources/order.avsc</order>
                                <flight>src/main/resources/flight.proto</flight>
                            </schemas>
                            <schemaTypes>
                                <flight>ProtoBuf</flight>
                            </schemaTypes>
                            <previousSchemaPaths>
                                <flight>src/main/resources/flightSchemas</flight>
                                <order>src/main/resources/orderSchemas</order>
                            </previousSchemaPaths>
                            <compatibilityLevels>
                                <order>FORWARD_TRANSITIVE</order>
                                <flight>FORWARD_TRANSITIVE</flight>
                            </compatibilityLevels>
                        </configuration>
                    </execution>

                    <execution>
                        <id>test-compatibility</id>
                        <phase>validate</phase>
                        <goals>
                            <goal>test-compatibility</goal>
                        </goals>
                        <configuration>
                            <subjects>
                                <Orders-value>src/main/resources/order.avsc</Orders-value>
                                <Flights-value>src/main/resources/flight.proto</Flights-value>
                            </subjects>
                            <schemaTypes>
                                <Flights-value>PROTOBUF</Flights-value>
                            </schemaTypes>
                        </configuration>
                    </execution>

                    <execution>
                        <id>register</id>
                        <goals>
                            <goal>register</goal>
                        </goals>
                        <configuration>
                            <subjects>
                                <Orders-value>src/main/resources/order.avsc</Orders-value>
                                <Flights-value>src/main/resources/flight.proto</Flights-value>
                            </subjects>
                            <schemaTypes>
                                <Flights-value>PROTOBUF</Flights-value>
                            </schemaTypes>
                        </configuration>
                    </execution>

                </executions>
            </plugin>

        </plugins>
    </build>


</project>

The following workflows can be coded as GitHub actions to accomplish CICD for schema management.

  1. When a pull request is created to merge a new schema to master, validate the schema, check local schema compatibility, set compatibility of subject, and test schema compatibility with subject.

    run: mvn validate

    The validate step would include:

    mvn schema-registry:validate@validate
mvn schema-registry:test-local-compatibility@test-local
mvn schema-registry:set-compatibility@set-compatibility
mvn schema-registry:test-compatibility@test-compatibility

    Integrated with GitHub Actions, the pull-request.yaml for this step might look like this:

    name: Testing branch for compatibility before merging
 on:
  pull_request:
  branches: [ master ]
  paths: [src/main/resources/*]
 jobs:

  validate:
    runs-on: ubuntu-latest
    steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-java@v2
         with:
           java-version: '11'
           distribution: 'temurin'
           cache: maven
       - name: Validate if schema is valid
         run: mvn schema-registry:validate@validate

  test-local-compatibility:
  needs: validate
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-java@v2
        with:
          java-version: '11'
          distribution: 'temurin'
          cache: maven
      - name: Test schema with locally present schema
        run: mvn schema-registry:test-local-compatibility@test-local

  set-compatibility:
    needs: test-local-compatibility
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-java@v2
        with:
          java-version: '11'
          distribution: 'temurin'
          cache: maven
      - name: Set compatibility of subject
        run: mvn schema-registry:set-compatibility@set-compatibility

  test-compatibility:
    needs: set-compatibility
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-java@v2
        with:
          java-version: '11'
          distribution: 'temurin'
          cache: maven
      - name: Test schema with subject
        run: mvn schema-registry:test-compatibility@test-compatibility

    If compatibility checking passes a new pull request is created for approval.

  2. Register schema when a pull request is approved and merged to master.

    Run the action to register the new schema on the Schema Registry:

    run: mvn schema-registry:register@register

    The push.yaml for this step would look like this:

    name: Registering Schema on merge of pull request
on:
  push:
    branches: [ master ]
    paths: [src/main/resources/*]
jobs:
  register-schema:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-java@v2
        with:
          java-version: '11'
          distribution: 'temurin'
          cache: maven
      - name: Register Schema
        run: mvn io.confluent:kafka-schema-registry-maven-plugin:register@register