Chapter 9. Using AMQ Streams with MirrorMaker 2.0

MirrorMaker 2.0 is used to replicate data between two or more active Kafka clusters, within or across data centers.

Data replication across clusters supports scenarios that require:

  • Recovery of data in the event of a system failure
  • Aggregation of data for analysis
  • Restriction of data access to a specific cluster
  • Provision of data at a specific location to improve latency

MirrorMaker 2.0 has features not supported by the previous version of MirrorMaker. However, you can configure MirrorMaker 2.0 to be used in legacy mode.

Additional resources

9.1. MirrorMaker 2.0 data replication

MirrorMaker 2.0 consumes messages from a source Kafka cluster and writes them to a target Kafka cluster.

MirrorMaker 2.0 uses:

  • Source cluster configuration to consume data from the source cluster
  • Target cluster configuration to output data to the target cluster

MirrorMaker 2.0 is based on the Kafka Connect framework, connectors managing the transfer of data between clusters. A MirrorMaker 2.0 MirrorSourceConnector replicates topics from a source cluster to a target cluster.

The process of mirroring data from one cluster to another cluster is asynchronous. The recommended pattern is for messages to be produced locally alongside the source Kafka cluster, then consumed remotely close to the target Kafka cluster.

MirrorMaker 2.0 can be used with more than one source cluster.

Figure 9.1. Replication across two clusters

MirrorMaker 2.0 replication

9.2. Cluster configuration

You can use MirrorMaker 2.0 in active/passive or active/active cluster configurations.

  • In an active/passive configuration, the data from an active cluster is replicated in a passive cluster, which remains on standby, for example, for data recovery in the event of system failure.
  • In an active/active configuration, both clusters are active and provide the same data simultaneously, which is useful if you want to make the same data available locally in different geographical locations.

The expectation is that producers and consumers connect to active clusters only.

9.2.1. Bidirectional replication

The MirrorMaker 2.0 architecture supports bidirectional replication in an active/active cluster configuration. A MirrorMaker 2.0 cluster is required at each target destination.

Each cluster replicates the data of the other cluster using the concept of source and remote topics. As the same topics are stored in each cluster, remote topics are automatically renamed by MirrorMaker 2.0 to represent the source cluster.

Figure 9.2. Topic renaming

MirrorMaker 2.0 bidirectional architecture

By flagging the originating cluster, topics are not replicated back to that cluster.

The concept of replication through remote topics is useful when configuring an architecture that requires data aggregation. Consumers can subscribe to source and remote topics within the same cluster, without the need for a separate aggregation cluster.

9.2.2. Topic configuration synchronization

Topic configuration is automatically synchronized between source and target clusters. By synchronizing configuration properties, the need for rebalancing is reduced.

9.2.3. Data integrity

MirrorMaker 2.0 monitors source topics and propagates any configuration changes to remote topics, checking for and creating missing partitions. Only MirrorMaker 2.0 can write to remote topics.

9.2.4. Offset tracking

MirrorMaker 2.0 tracks offsets for consumer groups using internal topics.

  • The offset sync topic maps the source and target offsets for replicated topic partitions from record metadata
  • The checkpoint topic maps the last committed offset in the source and target cluster for replicated topic partitions in each consumer group

Offsets for the checkpoint topic are tracked at predetermined intervals through configuration. Both topics enable replication to be fully restored from the correct offset position on failover.

MirrorMaker 2.0 uses its MirrorCheckpointConnector to emit checkpoints for offset tracking.

9.2.5. Connectivity checks

A heartbeat internal topic checks connectivity between clusters.

The heartbeat topic is replicated from the source cluster.

Target clusters use the topic to check:

  • The connector managing connectivity between clusters is running
  • The source cluster is available

MirrorMaker 2.0 uses its MirrorHeartbeatConnector to emit heartbeats that perform these checks.

9.3. ACL rules synchronization

If SimpleAclAuthorizer is being used, ACL rules that manage access to brokers also apply to remote topics. Users that can read a source topic can read its remote equivalent.


OAuth 2.0 authorization does not support access to remote topics in this way.

9.4. Synchronizing data between Kafka clusters using MirrorMaker 2.0

Use MirrorMaker 2.0 to synchronize data between Kafka clusters through configuration.

The previous version of MirrorMaker continues to be supported, by running MirrorMaker 2.0 in legacy mode.

The configuration must specify:

  • Each Kafka cluster
  • Connection information for each cluster, including TLS authentication
  • The replication flow and direction

    • Cluster to cluster
    • Topic to topic
  • Replication rules
  • Committed offset tracking intervals

This procedure describes how to implement MirrorMaker 2.0 by creating the configuration in a properties file, then passing the properties when using the MirrorMaker script file to set up the connections.


MirrorMaker 2.0 uses Kafka Connect to make the connections to transfer data between clusters. Kafka provides MirrorMaker sink and source connectors for data replication. If you wish to use the connectors instead of the MirrorMaker script, the connectors must be configured in the Kafka Connect cluster. For more information, refer to the Apache Kafka documentation.

Before you begin

A sample configuration properties file is provided in ./config/


  • You need AMQ Streams installed on the hosts of each Kafka cluster node you are replicating.


  1. Open the sample properties file in a text editor, or create a new one, and edit the file to include connection information and the replication flows for each Kafka cluster.

    The following example shows a configuration to connect two clusters, cluster-1 and cluster-2, bidirectionally. Cluster names are configurable through the clusters property.

    clusters=cluster-1,cluster-2 1
    cluster-1.bootstrap.servers=<my-cluster>-kafka-bootstrap-<my-project>:443 2 3
    cluster-2.bootstrap.servers=<my-cluster>-kafka-bootstrap-<my-project>:443 4 5
    cluster-1->cluster-2.enabled=true 6
    cluster-1->cluster-2.topics=.* 7
    cluster-2->cluster-1.enabled=true 8
    cluster-2->cluster-1B->C.topics=.* 9
    replication.policy.separator=- 10
    sync.topic.acls.enabled=false 11
    refresh.topics.interval.seconds=60 12
    refresh.groups.interval.seconds=60 13
    Each Kafka cluster is identified with its alias
    Connection information for cluster-1, using the bootstrap address and port 443. Both clusters use port 443 to connect to Kafka using OpenShift Routes
    The ssl. properties define TLS configuration for cluster-1.
    Connection information for cluster-2.
    The ssl. properties define the TLS configuration for cluster-2.
    Replication flow enabled from the cluster-1 cluster to the cluster-2 cluster
    Replicates all topics from the cluster-1 cluster to the cluster-2 cluster
    Replication flow enabled from the cluster-2 cluster to the cluster-1 cluster
    Replicates specific topics from the cluster-2 cluster to the cluster-1 cluster
    Policy to declare the reserved character used as the topic name separator.
    When enabled, ACLs are applied to synchronized topics. The default is false.
    The period between checks for new topics to synchronize.
    The period between checks for new consumer groups to synchronize.
  2. Start MirrorMaker with the cluster connection configuration and replication policies you defined in your properties file:

    su - kafka
    /opt/kafka/bin/ /config/

    MirrorMaker sets up connections between the clusters.

  3. Start ZooKeeper and Kafka in the target clusters:

    su - kafka
    /opt/kafka/bin/ -daemon /opt/kafka/config/
    su - kafka
    /opt/kafka/bin/ -daemon /opt/kafka/config/
  4. For each target cluster, verify that the topics are being replicated:

    /bin/ --zookeeper  <ZooKeeperAddress> --list

9.5. Using MirrorMaker 2.0 in legacy mode

This procedure describes how to configure MirrorMaker 2.0 to use it in legacy mode. Legacy mode supports the previous version of MirrorMaker.

The MirrorMaker script /opt/kafka/bin/ can run MirrorMaker 2.0 in legacy mode.


You need the properties files you currently use with the legacy version of MirrorMaker.

  • /opt/kafka/config/
  • /opt/kafka/config/


  1. Edit the MirrorMaker and files to turn off MirrorMaker 2.0 features.

    For example:

    replication.policy.class=org.apache.kafka.mirror.LegacyReplicationPolicy 1
    refresh.topics.enabled=false 2
    Emulate the previous version of MirrorMaker.
    MirrorMaker 2.0 features disabled, including the internal checkpoint and heartbeat topics
  2. Save the changes and restart MirrorMaker with the properties files you used with the previous version of MirrorMaker:

    su - kafka /opt/kafka/bin/ \
    --consumer.config /opt/kafka/config/ \
    --producer.config /opt/kafka/config/ \

    The consumer properties provide the configuration for the source cluster and the producer properties provide the target cluster configuration.

    MirrorMaker sets up connections between the clusters.

  3. Start ZooKeeper and Kafka in the target cluster:

    su - kafka
    /opt/kafka/bin/ -daemon /opt/kafka/config/
    su - kafka
    /opt/kafka/bin/ -daemon /opt/kafka/config/
  4. For the target cluster, verify that the topics are being replicated:

    /bin/ --zookeeper  <ZooKeeperAddress> --list