IPv6 seems unsupported for metrics-listener

[matrixbot]

This issue has been migrated from #6644.

---

Description

metrics-listener makes synapse crash when assigned an IPv6-bind_address

Steps to reproduce

Add

listeners:
  - type: metrics
    port: 19000
    bind_addresses:
      - '127.0.0.1'

to the /etc/matrix-synapse/homeserver.yaml and everything works, change it to either

listeners:
  - type: metrics
    port: 19000
    bind_addresses:
      - '::1'

or

listeners:
  - type: metrics
    port: 19000
    bind_addresses:
      - '127.0.0.1'
      - '::1'

and synapse will not start anymore, instead yielding the following traceback:

twisted: [] Traceback (most recent call last):
twisted: []   File "/usr/lib/python3/dist-packages/synapse/app/_base.py", line 271, in start
twisted: []     hs.start_listening(listeners)
twisted: []   File "/usr/lib/python3/dist-packages/synapse/app/homeserver.py", line 293, in start_listening
twisted: []     _base.listen_metrics(listener["bind_addresses"], listener["port"])
twisted: []   File "/usr/lib/python3/dist-packages/synapse/app/_base.py", line 160, in listen_metrics
twisted: []     start_http_server(port, addr=host, registry=RegistryProxy)
twisted: []   File "/usr/lib/python3/dist-packages/synapse/metrics/_exposition.py", line 242, in start_http_server
twisted: []     httpd = _ThreadingSimpleServer((addr, port), CustomMetricsHandler)
twisted: []   File "/usr/lib/python3.7/socketserver.py", line 452, in __init__
twisted: []     self.server_bind()
twisted: []   File "/usr/lib/python3.7/http/server.py", line 137, in server_bind
twisted: []     socketserver.TCPServer.server_bind(self)
twisted: []   File "/usr/lib/python3.7/socketserver.py", line 466, in server_bind
twisted: []     self.socket.bind(self.server_address)
twisted: [] socket.gaierror: [Errno -9] Address family for hostname not supported
twisted: [] Unhandled error in Deferred:
twisted: [] 
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/synapse/app/_base.py", line 271, in start
    hs.start_listening(listeners)
  File "/usr/lib/python3/dist-packages/synapse/app/homeserver.py", line 293, in start_listening
    _base.listen_metrics(listener["bind_addresses"], listener["port"])
  File "/usr/lib/python3/dist-packages/synapse/app/_base.py", line 160, in listen_metrics
    start_http_server(port, addr=host, registry=RegistryProxy)
  File "/usr/lib/python3/dist-packages/synapse/metrics/_exposition.py", line 242, in start_http_server
    httpd = _ThreadingSimpleServer((addr, port), CustomMetricsHandler)
  File "/usr/lib/python3.7/socketserver.py", line 452, in __init__
    self.server_bind()
  File "/usr/lib/python3.7/http/server.py", line 137, in server_bind
    socketserver.TCPServer.server_bind(self)
  File "/usr/lib/python3.7/socketserver.py", line 466, in server_bind
    self.socket.bind(self.server_address)
socket.gaierror: [Errno -9] Address family for hostname not supported

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python3/dist-packages/synapse/app/homeserver.py", line 413, in start
    _base.start(hs, config.listeners)
  File "/usr/lib/python3/dist-packages/synapse/app/_base.py", line 281, in start
    sys.exit(1)
SystemExit: 1

Version information

• Version: 1.7.3
• Install method: package manager/apt
• Platform: Debian 10 Buster, backports-repository