Ben Harrison Ben Harrison - 2 months ago 41
Python Question

How to subscribe to a list of multiple kafka wildcard patterns using kafka-python?

I'm subscribing to Kafka using a pattern with a wildcard, as shown below. The wildcard represents a dynamic customer id.

consumer.subscribe(pattern='customer.*.validations')


This works well, because I can pluck the customer Id from the topic string. But now I need to expand on the functionality to listen to a similar topic for a slightly different purpose. Let's call it
customer.*.additional-validations
. The code needs to live in the same project because so much functionality is shared, but I need to be able to take a different path based on the type of queue.

In the Kafka documentation I can see that it is possible to subscribe to an array of topics. However these are hard-coded strings. Not patterns that allow for flexibility.

>>> # Deserialize msgpack-encoded values
>>> consumer = KafkaConsumer(value_deserializer=msgpack.loads)
>>> consumer.subscribe(['msgpackfoo'])
>>> for msg in consumer:
... assert isinstance(msg.value, dict)


So I'm wondering if it is possible to somehow do a combination of the two? Kind of like this (non-working):

consumer.subscribe(pattern=['customer.*.validations', 'customer.*.additional-validations'])

Answer

In the KafkaConsumer code, it supports list of topics, or a pattern,

https://github.com/dpkp/kafka-python/blob/68c8fa4ad01f8fef38708f257cb1c261cfac01ab/kafka/consumer/group.py#L717

   def subscribe(self, topics=(), pattern=None, listener=None):
        """Subscribe to a list of topics, or a topic regex pattern
        Partitions will be dynamically assigned via a group coordinator.
        Topic subscriptions are not incremental: this list will replace the
        current assignment (if there is one).

So you can create a regex, with OR condition using |, that should work as subscribe to multiple dynamic topics regex, as it internally uses re module for matching.

(customer.*.validations)|(customer.*.additional-validations)

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