First, I'd recommend you use the official Couchbase image instead of
arungupta/couchbase, since that is not maintained.
Second, is your Go code running within the docker host? I suspect it is not, and that's the reason you're running into this issue. The Go client needs to be able to reach every Couchbase node. Outside of the docker host, it will only be able to get to one.
My recommendation is to move your Go client inside of the docker host.