Pulsar Flink Connector

The Pulsar Flink connector implements elastic data processing using Apache Pulsar and Apache Flink.

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Prerequisites

• Java 8 or higher version
• Flink 1.13.0 or higher version
• Pulsar 2.8.0 or higher version

Basic information

This section describes basic information about the Pulsar Flink connector.

Client

We change our project version definition, the Flink & Pulsar supporting matrix is here.

Version definitions

Since the JAR package to Maven central, you can use this connector by using Maven, Gradle, or sbt. There are two types of connector, the pulsar-flink-connector_2.11 for Scala 2.11, and the pulsar-flink-connector_2.12 for Scala 2.12. This naming style is the same as Flink. The version of this project is in a four-part form, the first three part is the relying Flink version, and the last part is the patching version for connector.

This version definition is simple for users to choose right connector. We do not shade the pulsar-client-all to the Distro. Instead, we just use the Maven dependency. You can override the dependent pulsar-client-all as long as its version is higher than the one listed in the supporting matrix.

Maven projects

For Maven projects, add the following dep to your pom. scala.binary.version is following the flink dependency style, you can add it in your pom properties field. ${pulsar-flink-connector.version} can be changed to your desired version, or defined it in pom properties field.

<dependency>
    <groupId>io.streamnative.connectors</groupId>
    <artifactId>pulsar-flink-connector_${scala.binary.version}</artifactId>
    <version>${pulsar-flink-connector.version}</version>
</dependency>

For Maven projects, you can use the following shade plugin definition template to build an application JAR package that contains all the dependencies required for the client library and Pulsar Flink connector.

<plugin>
  <!-- Shade all the dependencies to avoid conflicts -->
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-shade-plugin</artifactId>
  <version>${maven-shade-plugin.version}</version>
  <executions>
    <execution>
      <phase>package</phase>
      <goals>
        <goal>shade</goal>
      </goals>
      <configuration>
        <createDependencyReducedPom>true</createDependencyReducedPom>
        <promoteTransitiveDependencies>true</promoteTransitiveDependencies>
        <minimizeJar>false</minimizeJar>

        <artifactSet>
          <includes>
            <include>io.streamnative.connectors:*</include>
            <include>org.apache.pulsar:*</include>
            <!-- more libs to include here -->
          </includes>
        </artifactSet>
        <filters>
          <filter>
            <artifact>*:*</artifact>
            <excludes>
              <exclude>META-INF/*.SF</exclude>
              <exclude>META-INF/*.DSA</exclude>
              <exclude>META-INF/*.RSA</exclude>
            </excludes>
          </filter>
        </filters>
        <transformers>
          <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
          <transformer implementation="org.apache.maven.plugins.shade.resource.PluginXmlResourceTransformer" />
        </transformers>
      </configuration>
    </execution>
  </executions>
</plugin>

Gradle projects

For Gradle projects, make sure maven central is added to your build.gradle, as shown below.

repositories {
    mavenCentral()
}

For gradle projects, you can use the following shade plugin definition template to build an application JAR package that contains all the dependencies required for the client library and Pulsar Flink connector.

buildscript {
     dependencies {
         classpath 'com.github.jengelman.gradle.plugins:shadow:6.0.0'
     }
}

apply plugin: 'com.github.johnrengelman.shadow'
apply plugin: 'java'

Build Pulsar Flink connector

To build the Pulsar Flink connector for reading data from Pulsar or writing the results to Pulsar, follow these steps.

1. Check out the source code.

   git clone https://github.com/streamnative/pulsar-flink.git
   cd pulsar-flink

2. Install the Docker.

   The Pulsar Flink connector uses Testcontainers for integration test. To run the integration test, ensure to install the Docker. For details about how to install the Docker, see here.

3. Set the Java version.

   Modify java.version and java.binary.version in pom.xml.

   Note
   Ensure that the Java version should be identical to the Java version for the Pulsar Flink connector.

4. Build the project.

   mvn clean install -DskipTests

5. Run the test.

   mvn clean install

After the Pulsar Flink connector is installed, a JAR package that contains all the dependencies is generated in both the local Maven repository and the target directory.

Deploy Pulsar Flink connector

This section describes how to deploy the Pulsar Flink connector.

Client library

For any Flink application, use the ./bin/flink run command to compile and start your application.

If you have already built a JAR package with dependencies using the above shade plugin, you can use the --classpath option to add your JAR package.

Example

./bin/flink run -c com.example.entry.point.ClassName file://path/to/jars/your_fat_jar.jar

Scala REPL

The Scala REPL is a tool (scala) for evaluating expressions in Scala. Use the bin/start-scala-shell.sh command to deploy Pulsar Flink connector on Scala client. You can use the --addclasspath to add pulsar-flink-connector_{{SCALA_BINARY_VERSION}}-{{PULSAR_FLINK_VERSION}}.jar package.

Example

./bin/start-scala-shell.sh remote <hostname> <portnumber>
 --addclasspath pulsar-flink-connector_{{SCALA_BINARY_VERSION}}-{{PULSAR_FLINK_VERSION}}.jar

For more information on submitting applications through the CLI, see Command-Line Interface .

SQL client

The SQL Client is used to write SQL queries for manipulating data in Pulsar, you can use the -addclasspath option to add pulsar-flink-connector_{{SCALA_BINARY_VERSION}}-{{PULSAR_FLINK_VERSION}}.jar package.

Example

./bin/sql-client.sh embedded --jar pulsar-flink-connector_{{SCALA_BINARY_VERSION}}-{{PULSAR_FLINK_VERSION}}.jar

By default, to use the Pulsar directory in the SQL client and register it automatically at startup, the SQL client reads its configuration from the ./conf/sql-client-defaults.yaml environment file. You need to add the Pulsar catalog to the catalogs section of this YAML file, as shown below.

catalogs:
- name: pulsarcatalog
    type: pulsar
    default-database: tn/ns
    service-url: "pulsar://localhost:6650"
    admin-url: "http://localhost:8080"
    format: json

Usage

This section describes how to use the Pulsar Flink connector in the stream environment and table environment.

Stream environment

This section describes how to use the Pulsar Flink connector in the stream environment.

Source

In Pulsar Flink, the Pulsar consumer is called FlinkPulsarSource<T>. It accesses to one or more Pulsar topics.

Its constructor method has the following parameters.

• serviceUrl (service address) and adminUrl (administrative address): they are used to connect to the Pulsar instance.
• PulsarDeserializationSchema<T>: when the FlinkPulsarSource is used, you need to set the PulsarDeserializationSchema<T> parameter.
• Properties: it is used to configure the behavior of the Pulsar consumer, including the topic, topics, and topicsPattern options. The topic, topics, or topicsPattern option is used to configure information about the topic to be consumed. You must set a value for it. (The topics parameters refers to multiple topics separated by a comma (,), and the topicsPattern parameter is a Java regular expression that matches a number of topics.)
• setStartFromLatest, setStartFromEarliest, setStartFromSpecificOffsets, or setStartFromSubscription: these parameters are used to configure the consumption mode. When the setStartFromSubscription consumption mode is configured, the checkpoint function must be enabled.

Example

StreamExecutionEnvironment see = StreamExecutionEnvironment.getExecutionEnvironment();
Properties props = new Properties();
props.setProperty("topic", "test-source-topic");
props.setProperty("partition.discovery.interval-millis", "5000");

FlinkPulsarSource<String> source = new FlinkPulsarSource<>(serviceUrl, adminUrl, PulsarDeserializationSchema.valueOnly(new SimpleStringSchema()), props);

// or setStartFromLatest、setStartFromSpecificOffsets、setStartFromSubscription
source.setStartFromEarliest(); 

DataStream<String> stream = see.addSource(source);

// chain operations on dataStream of String and sink the output
// end method chaining

see.execute();

Sink

The Pulsar producer uses the FlinkPulsarSink instance. It allows to write record streams to one or more Pulsar topics.

Example

PulsarSerializationSchema<Person> pulsarSerialization = new PulsarSerializationSchemaWrapper.Builder<>(JsonSer.of(Person.class))
    .usePojoMode(Person. class, RecordSchemaType.JSON)
    .setTopicExtractor(person -> null)
    .build();
FlinkPulsarSink<Person> sink = new FlinkPulsarSink(
    serviceUrl,
    adminUrl,
    Optional.of(topic), // mandatory target topic or use `Optional.empty()` if sink to different topics for each record
    props,
    pulsarSerialization
);

stream.addSink(sink);

PulsarDeserializationSchema

PulsarDeserializationSchema is a connector-defined Flink DeserializationSchema wrapper that allows flexible manipulation of Pulsar messages.

PulsarDeserializationSchemaWrapper is a simple implementation of PulsarDeserializationSchema with two parameters: Flink DeserializationSchema and information about the decoded message type.

PulsarDeserializationSchemaWrapper(new SimpleStringSchema(),DataTypes.STRING())

PulsarSerializationSchema

PulsarSerializationSchema is a wrapper for Flink SerializationSchema that provides more functionality. In most cases, users do not need to implement PulsarSerializationSchema by themselves. PulsarSerializationSchemaWrapper is provided to wrap a Flink SerializationSchema as PulsarSerializationSchema.

PulsarSerializationSchema uses the builder pattern and you can call setKeyExtractor or setTopicExtractor to extract the key and customize the target topic from each message.

In particular, since Pulsar maintains its own Schema information internally, our messages must be able to export SchemaInfo when they are written to Pulsar. The useSpecialMode, useAtomicMode, usePojoMode, and useRowMode methods help you quickly build the Schema information required for Pulsar. You must choose one of these four modes.

• SpecialMode: specify the Schema<?> mode directly. Ensure that this Schema is compatible with the Flink SerializationSchema setting.
• AtomicMode: For some atomic types, pass the type of AtomicDataType, such as DataTypes.INT(), which corresponds to Schema<Integer> in Pulsar.
• PojoMode: you need to pass a custom class object and either JSON or Arvo Schema to specify how to build a composite type Schema, such as usePojoMode(Person.class, RecordSchemaType.JSON).
• RowMode: in general, it is used for our internal Table&SQL API implementation.

Fault tolerance

With Flink's checkpoints being enabled, FlinkPulsarSink can provide at-least-once and exactly-once delivery guarantees.

In addition to enabling checkpoints for Flink, you should also configure setLogFailuresOnly(boolean) and setFlushOnCheckpoint(boolean) parameters.

Table environment

The Pulsar Flink connector supports all the Table features, as listed below.

• SQL and DDL
• Catalog

SQL and DDL

The following section describes SQL configurations and DDL configurations.

SQL configurations

CREATE TABLE pulsar (
  `physical_1` STRING,
  `physical_2` INT,
  `eventTime` TIMESTAMP(3) METADATA,
  `properties` MAP<STRING, STRING> METADATA ,
  `topic` STRING METADATA VIRTUAL,
  `sequenceId` BIGINT METADATA VIRTUAL,
  `key` STRING ,
  `physical_3` BOOLEAN
) WITH (
  'connector' = 'pulsar',
  'topic' = 'persistent://public/default/topic82547611',
  'key.format' = 'raw',
  'key.fields' = 'key',
  'value.format' = 'avro',
  'service-url' = 'pulsar://localhost:6650',
  'admin-url' = 'http://localhost:8080',
  'scan.startup.mode' = 'earliest' 
)

INSERT INTO pulsar 
VALUES
 ('data 1', 1, TIMESTAMP '2020-03-08 13:12:11.123', MAP['k11', 'v11', 'k12', 'v12'], 'key1', TRUE),
 ('data 2', 2, TIMESTAMP '2020-03-09 13:12:11.123', MAP['k21', 'v21', 'k22', 'v22'], 'key2', FALSE),
 ('data 3', 3, TIMESTAMP '2020-03-10 13:12:11.123', MAP['k31', 'v31', 'k32', 'v32'], 'key3', TRUE)
 
SELECT * FROM pulsar

SQL supports configuring physical fields, calculated columns, watermark, METADATA and other features.

DDL configurations

Metadata configurations

The METADATA flag is used to read and write metadata in Pulsar messages. The support list is as follows.

Catalog

Flink always searches for tables, views and UDFs in the current catalog and database. To use the Pulsar Catalog and treat the topic in Pulsar as a table in Flink, you should use the pulsarcatalog that has been defined in ./conf/sql-client-defaults.yaml in pulsarcatalog.

tableEnv.useCatalog("pulsarcatalog")
tableEnv.useDatabase("public/default")
tableEnv.scan("topic0")

Flink SQL> USE CATALOG pulsarcatalog;
Flink SQL> USE `public/default`;
Flink SQL> select * from topic0;

The following configuration is optional in the environment file, or it can be overridden in the SQL client session using the SET command.

For more details, see DDL configurations.

Advanced features

This section describes advanced features supported by Pulsar Flink connector.

Pulsar primitive types

Pulsar provides some basic native types. To use these native types, you can support them in the following ways.

Stream API environment

PulsarPrimitiveSchema is an implementation of the PulsarDeserializationSchema and PulsarSerializationSchema interfaces.

You can create the required instance in a similar way new PulsarSerializationSchema(String.class).

Table environment

We have created a new Flink format component called atomic that you can use in SQL format. In Source, it translates the Pulsar native type into only one column of RowData. In Sink, it translates the first column of RowData into the Pulsar native type and writes it to Pulsar.

Upsert Pulsar

There is an increasing demand for Upsert mode message queues for three main reasons.

• Interpret the Pulsar topic as a changelog stream, which interprets records with keys as Upsert events.
• As part of the real-time pipeline, multiple streams are connected for enrichment and the results are stored in the Pulsar topic for further computation. However, the results may contain updated events.
• As part of the real-time pipeline, the data stream is aggregated and the results are stored in Pulsar Topic for further computation. However, the results may contain updated events.

Based on these requirements, we support Upsert Pulsar. With this feature, users can read data from and write data to Pulsar topics in an Upsert fashion.

In the SQL DDL definition, you can set the connector to upsert-pulsar to use the Upsert Pulsar connector.

In terms of configuration, the primary key of the Table must be specified, and key.fields, key.fields-prefix cannot be used.

As a source, the Upsert Pulsar connector produces changelog streams, where each data record represents an update or deletion event. More precisely, the value in a data record is interpreted as a UPDATE of the last value of the same key, if this key exists (If the corresponding key does not exist, the UPDATE is considered as an INSERT.). Using the table analogy, data records in the changelog stream are interpreted as UPSERT, also known as INSERT/UPDATE, because any existing row with the same key is overwritten. Also, a message with a null value is treated as a DELETE message.

As a sink, the Upsert Pulsar connector can consume changelog streams. It writes INSERT/UPDATE_AFTER data as normal Pulsar messages and writes DELETE data as Pulsar messages with null value (It indicates that key of the message is deleted). Flink partitions the data based on the value of the primary key so that the messages on the primary key are ordered. And, UPDATE/DELETE messages with the same primary key fall in the same partition.

Key-Shared subscription mode

In some scenarios, users need messages to be strictly guaranteed message order to ensure correct business processing. Usually, in the case of strictly order-preserving messages, only one consumer can consume messages at the same time to guarantee the order. This results in a significant reduction in message throughput. Pulsar designs the Key-Shared subscription mode for such scenarios by adding keys to messages and routing messages with the same Key Hash to the same messenger, which ensures message order and improves throughput.

Pulsar Flink connector supports this feature the as well. This feature can be enabled by configuring the enable-key-hash-range=true parameter. When enabled, the range of Key Hash processed by each consumer is divided based on the parallelism of the task.

Fault tolerance

Pulsar Flink connector 2.7.0 provides different semantics for source and sink.

Source

For Pulsar source, Pulsar Flink connector 2.7.0 provides exactly-once semantic.

Sink

Pulsar Flink connector 2.4.12 only supports at-least-once semantic for sink. Based on transactions supported in Pulsar 2.7.0 and the Flink TwoPhaseCommitSinkFunction API, Pulsar Flink connector 2.7.0 supports both exactly-once and at-least-once semantics for sink. For more information, see here.

Before setting exactly_once semantic for a sink, you need to make the following configuration changes.

1. In Pulsar, transaction related functions are disabled by default. In this case, you need to set transactionCoordinatorEnabled = true in the configuration file (conf/standalone.conf or conf/broker.conf) .

2. When creating a sink, set PulsarSinkSemantic.EXACTLY_ONCE. The default value of PulsarSinkSemantic is AT_LEAST_ONCE.

   Example

   SinkFunction<Integer> sink = new FlinkPulsarSink<>(
         adminUrl,
         Optional.of(topic),
         clientConfigurationData,
         new Properties(),
         new PulsarSerializationSchemaWrapper.Builder<>
                 ((SerializationSchema<Integer>) element -> Schema.INT32.encode(element))
                 .useAtomicMode(DataTypes.INT())
                 .build(),
         PulsarSinkSemantic.EXACTLY_ONCE
   );
   

   Additionally, you can set transaction related configurations as below.

   Parameter	Description	Default value
   PulsarOptions.TRANSACTION_TIMEOUT	Timeout for transactions in Pulsar. If the time exceeds, the transaction operation fails.	360000ms
   PulsarOptions.MAX_BLOCK_TIME_MS	Maximum time to wait for a transaction to commit or abort. If the time exceeds, the operator throws an exception.	100000ms

   Alternatively, you can override these configurations in the Properties object and pass it into the Sink constructor.

Configuration parameters

This parameter corresponds to the FlinkPulsarSource in StreamAPI, the Properties object in the FlinkPulsarSink construction parameter, and the configuration properties parameter in Table mode.

pulsar.reader.* and pulsar.producer.* specify more detailed configuration of the Pulsar behavior. The asterisk sign (*) is replaced by the configuration name in Pulsar. For details, see Pulsar reader and Pulsar producer.

In the DDL statement, the sample which is similar to the following is used.

'properties.pulsar.reader.subscriptionRolePrefix' = 'pulsar-flink-',
'properties.pulsar.producer.sendTimeoutMs' = '30000',

Authentication configuration

For Pulsar instances configured with authentication, the Pulsar Flink connector can be configured in a similar as the regular Pulsar client.

1. For FlinkPulsarSource and FlinkPulsarSink on Java API, you can use one of the following ways to set up authentication.

   • Set the Properties parameter.

     props.setProperty(PulsarOptions.AUTH_PLUGIN_CLASSNAME_KEY, "org.apache.pulsar.client.impl.auth.AuthenticationToken");
     props.setProperty(PulsarOptions.AUTH_PARAMS_KEY, "token:abcdefghijklmn");

   • Set the ClientConfigurationData parameter, which has a higher priority than the Properties parameter.

     ClientConfigurationData conf = new ClientConfigurationData();
     conf.setServiceUrl(serviceUrl);
     conf.setAuthPluginClassName(className);
     conf.setAuthParams(params);

2. For the Table and SQL, you can use the following way to set up authentication.

   CREATE TABLE pulsar (
                          `physical_1` STRING,
                          `physical_2` INT,
                          `eventTime` TIMESTAMP(3) METADATA,
                          `properties` MAP<STRING, STRING> METADATA ,
                          `topic` STRING METADATA VIRTUAL,
                          `sequenceId` BIGINT METADATA VIRTUAL,
                          `key` STRING ,
                          `physical_3` BOOLEAN
   ) WITH (
       'connector' = 'pulsar',
       'topic' = 'persistent://public/default/topic82547611',
       'key.format' = 'raw',
       'key.fields' = 'key',
       'value.format' = 'avro',
       'service-url' = 'pulsar://localhost:6650',
       'admin-url' = 'http://localhost:8080',
       'scan.startup.mode' = 'earliest',
       'properties.auth-plugin-classname' = 'org.apache.pulsar.client.impl.auth.AuthenticationToken',
       'properties.auth-params' = 'token:xxxxxxxxxx',
   )

For details about authentication configuration, see Pulsar Security.

ProtoBuf

This feature is based on this PR and is not merged yet. Therefore, it is temporarily placed in this repository as a source code for packaging and dependencies.

Example

create table pulsar (
                        a INT,
                        b BIGINT,
                        c BOOLEAN,
                        d FLOAT,
                        e DOUBLE,
                        f VARCHAR(32),
                        g BYTES,
                        h VARCHAR(32),
                        f_abc_7d INT,
                        `eventTime` TIMESTAMP(3) METADATA,
                        compute as a + 1,
                        watermark for eventTime as eventTime
                        ) with (
                        'connector' = 'pulsar',
                        'topic' = 'test-protobuf',
                        'service-url' = 'pulsar://localhost:6650',
                        'admin-url' = 'http://localhost:8080',
                        'scan.startup.mode' = 'earliest',
                        'format' = 'protobuf',
                        'protobuf.message-class-name' = 'org.apache.flink.formats.protobuf.testproto.SimpleTest'
                        )

INSERT INTO pulsar VALUES (1,2,false,0.1,0.01,'haha', ENCODE('1', 'utf-8'), 'IMAGES',1, TIMESTAMP '2020-03-08 13:12:11.123');

The SimpleTest class must be GeneratedMessageV3.