Known Issues in Streams Replication Manager

This topic describes known issues for using Streams Replication Manager in this release of Cloudera Runtime.

Known Issues

SRM does not sync re-created source topics until the offsets have caught up with target topic: Messages written to topics that were deleted and re-created are not replicated until the source topic reaches the same offset as the target topic. For example, if at the time of deletion and re-creation there are a 100 messages on the source and target clusters, new messages will only get replicated once the re-created source topic has 100 messages. This leads to messages being lost.; N/A.

SRM may automatically re-create deleted topics: If auto.create.topics.enable is enabled, deleted topics are automatically recreated on source clusters.; Prior to deletion, remove the topic from the topic whitelist with the tool. This prevents topics from being re-created.
srm-control topics --source [SOURCE_CLUSTER] --target [TARGET_CLUSTER] --remove [TOPIC1][TOPIC2]

CSP-462: Replication failing when SRM driver is present on multiple nodes: Kafka replication fails when the SRM driver is installed on more than one node.; N/A.

CDPD-11074: The srm-control tool can be called without --target: srm-control; The srm-control tool can be initialized without specifying the --target option. If the tool is called this way it will fail to run correctly.; Do not use the tool without specifying the --target option. Always specify both --source and --target options. For example:
srm-control topics --source [SOURCE_CLUSTER] --target [TARGET_CLUSTER] --list

CDPD-13864 and CDPD-15327: Replication stops after the network configuration of a source or target cluster is changed

If the network configuration of a cluster which is taking part in a replication flow is changed, for example, port numbers are changed as a result of enabling or disabling TLS, SRM will not update its internal configuration even if SRM is reconfigured and restarted. From SRM’s perspective, it is the cluster identity that has changed. SRM cannot determine whether the new identity corresponds to the same cluster or not, only the owner or administrator of that cluster can know. In this case, SRM tries to use the last known configuration of that cluster which might not be valid, resulting in the halt of replication.

There are three workarounds for this issue. Choose one of the following:

Increase the driver rebalance timeout

Increasing the rebalance timeout to 5 minutes (300000 ms) or longer can resolve the issue. In general a 5 minute timeout should be sufficient for most deployments. However, depending on your scenario, an even longer period might be required. Increasing the rebalance timeout might lead to increased latency when the SRM drivers stop. The cluster will be slower when it rebalances the load of the removed driver.

The rebalance timeout can be configured on a per cluster (alias) basis by adding the following to the Streams Replication Manager’s Replication Configs Cloudera Manager property:

[***ALIAS***].rebalance.timeout.ms = [***VALUE***]

Replace [***ALIAS***] with a cluster alias specified in Streams Replication Manager Cluster alias. Do this for all clusters that are taking part in the replication process. When correctly configured, your configuration will have a rebalance.timeout.ms entry corresponding to each cluster (alias). For example:

primary.rebalance.timeout.ms = 30000
secondary.rebalance.timeout.ms = 30000
tertiary.rebalance.timeout.ms = 30000

After the new broker configuration is applied by SRM, the rebalance timeout can be reverted back to its original value, or removed from the configuration altogether.

Decrease replication admin timeout

Decreasing the replication admin timeout to 15 seconds (15000 ms) can resolve the issue. With higher loads, this might cause WARN messages to appear in the SRM driver log.

The admin timeout can be configured on a per replication basis by adding the following to the Streams Replication Manager’s Replication Configs Cloudera Manager property:

[***REPLICATION***].admin.timeout.ms = [***VALUE***]

Replace [***REPLICATION***] with a replication specified in Streams Replication Manager’s Replication Configs. Do this for all affected replications. When correctly configured, your configuration will have an admin.timeout.ms entry corresponding to each affected replication. For example:

primary->secondary.admin.timeout.ms = 15000
secondary->primary.admin.timeout.ms = 15000

After the new broker configuration is applied by SRM, the admin timeout can be reverted back to its original value, or removed from the configuration altogether.

Upgrade the brokers incrementally

Instead of switching over to the new configuration, open two separate listeners on the broker. One for the old configuration, and one for the new configuration. After updating SRM's configuration and restarting SRM, the old listener can be turned off. Non–inter-broker listeners can be configured with the dynamic configuration API of Kafka, this way not every listener change has to be followed by a restart.

CSP-956: Topics or groups added to white or blacklists are not returned when using srm-control --list: When polling the srm-control.<alias>.internal internal configuration topic, it may happen that not all records are returned at once. It can happen that the first poll only returns a single message. Remaining messages are only returned on a subsequent poll. As a result, only parts of the configuration are picked up. This causes the srm-control tool and the SRM driver to behave erratically as they are unable to read the full white and blacklists from the configuration topic.; N/A.

CDPD-11709: Blacklisted topics appear in the list of replicated topics: If a topic was originally replicated but was later blacklisted, it will still appear as a replicated topic under the /remote-topics REST API endpoint. As a result, if a call is made to this endpoint, the blacklisted topic will be included in the response. Additionally, the blacklisted topic will also be visible in the SMM UI. However, it's Partitions and Consumer Groups will be 0, its Throughput, Replication Latency and Checkpoint Latency will show N/A.; N/A.

CDPD-18300: SRM resolves configuration provider references in its internal configuration topic: SRM saves its internal configuration topic with fully resolved properties. This means that even configuration provider references are resolved. Sensitive information can be emitted into the configuration topic this way.; N/A.

CDPD-22094: The SRM service role displays as healthy, but no metrics are processed: The SRM service role might encounter errors that make metrics processing impossible. An example of this is when the target Kafka cluster is not reachable. The SRM service role does not automatically stop or recover if such an error is encountered. It continues to run and displays as healthy in Cloudera Manager. Metrics, however, are not processed. In addition, no new data is displayed in SMM for the replications.; Ensure that all clusters are available and are in a healthy state.

Restart SRM.

CDPD-22389: The SRM driver role displays as healthy, but replication fails: During startup, the SRM driver role might encounter errors that make data replication impossible. An example of this is when one of the clusters added for replication is not reachable. The SRM driver role does not automatically stop or recover if such an error is encountered. It will start up, continue to run, and display as healthy in Cloudera Manager. Replication, however, will not happen.; Ensure that all clusters are available and are in a healthy state.

Restart SRM.

CDPD-23683: The replication status reported by the SRM service role for healthy replications is flaky: The replication status reported by the SRM service role is flaky. The replication status might change between active and inactive frequently even if the replication is healthy. This status is also reflected in SMM on the replications tab.; None

Limitations

SRM cannot replicate Ranger authorization policies to or from Kafka clusters: Due to a limitation in the Kafka-Ranger plugin, SRM cannot replicate Ranger policies to or from clusters that are configured to use Ranger for authorization. If you are using SRM to replicate data to or from a cluster that uses Ranger, disable authorization policy synchronization in SRM. This can be achieved by clearing the Sync Topic Acls Enabled (sync.topic.acls.enabled) checkbox.