How to setup a connection between Python Couchbase SDK and containerized Couchbase nodes?

I want to have the following setup:

3 Couchbase nodes, each running on a separate container, all in the same cluster
Python application running in another container (querying, inserting, deleting data from the Couchbase cluster)

What I managed to do: Set up a cluster, bucket, query the bucket via UI (accessed by localhost:8091)

What I didn't manage to do: Create a connection between a Python application (which would at the end be Dockerized, for now for the sake of simplicity, let's treat it as local) and the (already working) cluster. Unfortunately, I cannot access it via Docker containers IP's with 8091 port, via localhost too. Unfortunately, the Couchbase documentation is either severely lacking here, or I just don't understand it. I tried to even use the setting-alternate-address option, but without much success (maybe I used it wrongly, so if you have any "how-to's" explaining the process, I'd still be grateful)

The connection works if there is one node, but throws Timeout if I set up 3 nodes.

I would really appreciate any tips leading to solving this problem.

EDIT: Adding code and error message:

    connection_string = "couchbase://localhost"
    cluster = Cluster.connect(connection_string, ClusterOptions(PasswordAuthenticator(os.getenv("LOGIN"), os.getenv("PASSWORD"))))
    # following a successful authentication, a bucket can be opened.
    # access a bucket in that cluster
    bucket = cluster.bucket('travel-sample')
    coll = bucket.default_collection()
    result = coll.get('airline_10')
    print(result.content_as[dict])

Error message:

couchbase.exceptions.UnAmbiguousTimeoutException: <ec=14, category=couchbase.common, message=unambiguous_timeout, context=KeyValueErrorContext:{'key': 'airline_10', 'bucket_name': 'travel-sample', 'scope_name': '_default', 'collection_name': '_default', 'opaque': 0}, C Source=C:\Jenkins\workspace\python\sdk\python-scripted-build-pipeline\py-client\src\kv_ops.cxx:209>

Solution

Couchbase SDKs need to be able to connect to every node on the cluster.

If you are running an app outside of the Docker host, it cannot connect to every node (you can't expose every node on the same port).

This is exactly why it will work fine with one node, but not with multiple (more details in the documentation)

If you run the Python app inside of a container that runs in the Docker host, it should connect just fine (or stick to a single node for development - which is mostly fine if you're not testing something specific to clustering/failover/replication).