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0005-optional-import-of-confluent-kafka.rst

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5. Optional import of confluent-kafka

Status

Accepted

Context

  • confluent-kafka is a library written and maintained by Confluent, our managed instance provider (see :doc:`0004-kafka-managed-hosting`). The library abstracts out the work for sending and receiving events to and from the Kafka cluster and converting them into message objects.
  • confluent-kafka in turn is a wrapper around a C library called librdkafka (distributed as librdkafka_dev)
  • librdkafka-dev does not currently have a compiled binary available for Linux/aarch64

As a result of the points above, if a package includes a dependency on confluent-kafka, installation will fail in Linux/aarch64 environments. This is a particular problem for developers who are using Tutor on an M1 Mac. Tutor is the standard distribution for Open edX developers and maintainers, so this is a significant issue for a large part of the community.

Decision

Instead of requiring confluent-kafka directly in base.in, we will wrap all imports of confluent_kafka in a try...catch block. If the import fails, the library will log an informative message and any calls will fail gracefully.

For example:

# See https://github.com/openedx/event-bus-kafka/blob/main/docs/decisions/0005-optional-import-of-confluent-kafka.rst
try:
    import confluent_kafka
    from confluent_kafka import DeserializingConsumer
except ImportError:  # pragma: no cover
    confluent_kafka = None

Then, later on, before any usage of DeserializingConsumer:

if not confluent_kafka:  # pragma: no cover
    warn("Confluent_kafka not installed")
    return None
...do things with DeserializingConsumer

For test modules, we can do something simpler; we'll always run tests with confluent_kafka installed (it's in test.in) and so do not need to set and check a flag. However, the import should still be allowed to fail silently on the off-chance that a test module is somehow loaded by tooling in a relying IDA. So, test modules can do something like this:

# See https://github.com/openedx/event-bus-kafka/blob/main/docs/decisions/0005-optional-import-of-confluent-kafka.rst
try:
    from confluent_kafka import DeserializingConsumer
except ImportError:  # pragma: no cover
    pass

Consequences

This will make developers or other users of the edx-event-bus-kafka library responsible for installing confluent-kafka in their own environments.

For edx.org, we will install confluent-kafka as part of creating the docker containers that will run the services that use this library.

Rejected Alternatives

  • Make the entire edx-event-bus-kafka library an optional dependency in the services that use it (eg edx-platform, course-discovery)

This would require developers to install edx-event-bus-kafka separately when setting up their environment. This means it would not be able to be updated with make upgrade in the same way we manage versions of all of our other packages. Moreover, this would require separate commits to update the version of the package and update the code that uses it, meaning we would have to use an expand-contract release model for every breaking change. This goes against best practices, being highly error-prone.

We expect edx-event-bus-kafka to change more frequently than confluent-kafka, which is why we are more willing to adopt the optional dependency strategy for the latter.

  • Keep both confluent-kafka and edx-event-bus-kafka as required dependencies

While not necessarily causing problems for edx.org, this would break many community-hosted Open edX instances as well as many development environments.