Enable full IPv6 support for synapse

[telmich]

Description:

At the moment synapse cannot be used with workers in IPv6 only environments, as the connection to redis fails and thus no communication is possible. There are various issues existing in the synapse repository and some in the twisted repository.

Feature

• Allow fully functional, worker based setup of synapse in IPv6 only environments
• Ensure that the functionality is covered by unit/integration tests

Bug Bounty

I would like to put a bounty on solving this bug to finally enable us and the community to run synapse properly in IPv6 only environments. I have an amount in CHF in my mind which I think is appropriate, but if you are interested in solving this as a paid gig, please reach out to me at ipv6only-bounty at ungleich.ch with a proposal on the time frame until it can be solved and which amount you think is appropriate.

[dklimpel]

Related to:

• In IPv6-only environment, can't connect to Redis due to DNS only looking for A records #10694
• Synapse can't connect to an IPv6-only mail server via hostname #7720
• v1.15 upgrade broken ipv6 replication config (ipv6 literals) #7695
• IPv6 seems unsupported for metrics-listener #6644
• Federation fails when using a DNS server on a link-local IPv6 address #5846
• Synapse fails to talk to appservices that listen on an IPv6 address. #4092
• Synapse completely hangs every few minutes, when configured with an IPv6 DNS server but no IPv6 network #2395
• Tests for IPv6 bugs / redis replication over IPv6 #11508
• Synapse does AAAA lookups even when IPv6 is disabled #14299

[telmich]

@dklimpel Thanks a lot for cross referencing, I wasn't even aware that there are that many outstanding bugs!

[anoadragon453]

A few comments in the above linked issues point to python-hyper/hyperlink#68 being the culprit.

There's a workaround noted in the issue. It may be worthwhile for one to go in and monkeypatch the workaround in to hyperlink and see if that fixes IPv6 connectivity in Synapse?