Invitations weren't working for me until I added 'nocanon' to these additional places. Until then, invitations failed with "Invalid signature for server ..." errors, as in https://github.com/matrix-org/synapse/issues/3294 .
I didn't check whether the user_directory/search proxy line also needs it, I just assumed it should have it too.
The other two proxy lines in this example also include a 'retry=0' parameter. That's a separate issue; I haven't touched it here.
Continuation of 1f0cc92b33.
As an explanation for the problem:
when saying `localhost` on the host, it sometimes gets resolved to `::1`
and sometimes to `127.0.0.1`. On the unfortunate occassions that
it gets resolved to `::1`, the container won't be able to serve the
request, because Docker containers don't have IPv6 enabled by default.
To avoid this problem, we simply prevent any lookups from happening
and explicitly use `127.0.0.1`.
