Replication request exceeds max size when trying to join room

Description

I’m getting the following error when trying to join #irc:matrix.org:

2021-05-07 20:16:08,373 - synapse.http.site - 107 - WARNING - sentinel - Aborting connection from IPv4Address(type='TCP', host='127.0.0.1', port=44100) because the request exceeds maximum size
2021-05-07 20:16:08,375 - synapse.http.site - 312 - INFO - sentinel - Connection from IPv4Address(type='TCP', host='127.0.0.1', port=44100) lost before request headers were read
2021-05-07 20:16:08,376 - synapse.http.client - 440 - INFO - POST-3 - Received response to POST http://127.0.0.1:9893/_synapse/replication/remote_join/%21BAXLHOFjvDKUeLafmO%3Amatrix.org/%40deepbluev7%3Aneko.dev/qjkxpFkuVk: 502
2021-05-07 20:16:08,376 - synapse.http.server - 88 - INFO - POST-3 - <SynapseRequest at 0x7f0f95586d00 method='POST' uri='/_matrix/client/r0/join/%23irc%3Amatrix.org' clientproto='HTTP/1.0' site=8086> SynapseError: 502 - Failed to talk to 
main process
2021-05-07 20:16:08,377 - synapse.access.http.8086 - 387 - INFO - POST-3 - 127.0.0.1 - 8086 - {@deepbluev7:neko.dev} Processed request: 27.573sec/-0.000sec (0.005sec, 0.001sec) (0.002sec/0.008sec/10) 64B 502 "POST /_matrix/client/r0/join/%
23irc%3Amatrix.org HTTP/1.0" "mtxclient v0.5.1" [0 dbevts]

I have a few workers with an event_creator and persister as well as a master and a few federation workers. This is from the event_creator log. Increasing the maximum size in https://github.com/matrix-org/synapse/blob/3ff225175462dde8376aa584e3a47c43b1f0e790/synapse/http/site.py#L106 made the join work.

Steps to reproduce

• Setup synapse with event_creator
• Try to join #irc:matrix.org

Version information

• Homeserver:

If not matrix.org: neko.dev

• Version: 1.33.1

• Install method: custom ebuild

• Platform: Gentoo

[erikjohnston]

I think https://github.com/matrix-org/synapse/pull/10082 might fix this?

[richvdh]

this was introduced by #9817.