Limitations

Known limitations for the DC/OS Apache Kafka service

Out-of-band configuration

Out-of-band configuration modifications are not supported. The service’s core responsibility is to deploy and maintain the service with a specified configuration. In order to do this, the service assumes that it has ownership of task configuration. If an end-user makes modifications to individual tasks through out-of-band configuration operations, the service will override those modifications at a later time. For example:

  • If a task crashes, it will be restarted with the configuration known to the scheduler, not one modified out-of-band.
  • If a configuration update is initiated, all out-of-band modifications will be overwritten during the rolling update.

Scaling

To prevent accidental data loss, the service does not support reducing the number of pods.

Disk changes

To prevent accidental data loss from reallocation, the service does not support changing volume requirements after initial deployment.

Best-effort installation

If your cluster does not have enough resources to deploy the service as requested, the initial deployment will not complete until either those resources are available or until you reinstall the service with corrected resource requirements. Similarly, scale-outs following initial deployment will not complete if the cluster does not have the needed available resources to complete the scale-out.

Virtual networks

When the service is deployed on a virtual network, the service may not be switched to host networking without a full re-installation. The same is true for attempting to switch from host to virtual networking.

Task Environment Variables

Each service task has some number of environment variables, which are used to configure the task. These environment variables are set by the service scheduler. While it is possible to use these environment variables in adhoc scripts (e.g. via dcos task exec), the name of a given environment variable may change between versions of a service and should not be considered a public API of the service.

Zones

If the service is deployed with a Zone constraint it may not be removed after initial installation.

Additionally, if the service was deployed without a Zone constraint, it may not have one added after initial installation.

Regions

The service cannot be moved between regions. It is also not possible to update the service to use a region if initially installed without one.

Log Retention Bytes

The disk configuration value is denominated in MB. We recommend you set the configuration value log_retention_bytes to a value smaller than the indicated disk configuration. See the Configuration section for instructions on customizing these values.

Security

Kafka CLI

When any security functions are enabled, the Kafka service CLI sub-command topic will not function. While the service CLI convenience functions will not work, the tooling bundled with Apache Kafka and other tools that support the enabled security modes will work.

Kerberos

When Kerberos is enabled, the broker VIP is disabled, as Kerberized clients will not be able to use it. This is because each Kafka broker uses a specific Kerberos principal and cannot accept connections from a single unified principal which the VIP would require.

Toggling Kerberos

Kerberos authentication can be toggled (enabled/disabled), but this triggers a rolling restart of the cluster. Clients configured with the old security settings will lose connectivity during and after this process. We recommend that you back up your files and schedule downtime.

Toggling Transport Encryption

Transport encryption using TLS can be toggled (enabled/disabled), but this triggers a rolling restart of the cluster. As each broker restarts, a client may lose connectivity based on its security settings and the value of the service.security.transport_encryption.allow_plaintext configuration option. We recommend that you back up your files and schedule downtime.

To enable TLS, a service account and corresponding secret is required. Since it is not possible to change the service account used by a service, we recommend that the service be deployed with an explicit service account, to allow for TLS to be enabled at a later stage.