### Background
As part of Element's plan to support a light form of vhosting (virtual
host) (multiple instances of Synapse in the same Python process), we're
currently diving into the details and implications of running multiple
instances of Synapse in the same Python process.
"Clean tenant provisioning" tracked internally by
https://github.com/element-hq/synapse-small-hosts/issues/221
### Partial startup problem
In the context of Synapse Pro for Small Hosts, since the Twisted reactor
is already running (from the `multi_synapse` shard process itself), when
provisioning a homeserver tenant, the `reactor.callWhenRunning(...)`
callbacks will be invoked immediately. This includes the Synapse's
[`start`](0615b64bb4/synapse/app/homeserver.py (L418-L429))
callback which sets up everything (including listeners, background
tasks, etc). If we encounter an error at this point, we are partially
setup but the exception will [bubble back to
us](8be122186b/multi_synapse/app/shard.py (L114-L121))
without us having a handle to the homeserver yet so we can't call
`hs.shutdown()` and clean everything up.
### What does this PR do?
Structures Synapse so we split creating the homeserver instance from
setting everything up. This way we have access to `hs` if anything goes
wrong during setup and can subsequently `hs.shutdown()` to clean
everything up.
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
* Fix#15669: always populate instance map even if it was empty
* Fix some tests
* Fix more tests
* Newsfile
Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>
* CI fix: don't forget to update apt repository sources before installing olddeps deps
* Add test testing the backwards compatibility
---------
Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>
* Add check to catch syanpse master process starting when workers are configured
* add test to verify that starting master process with worker config raises error
* newsfragment
* specify config.worker.worker_app in check
* update test
* report specific config option that triggered the error
Co-authored-by: reivilibre <oliverw@matrix.org>
* clarify error message
Co-authored-by: reivilibre <oliverw@matrix.org>
Co-authored-by: reivilibre <oliverw@matrix.org>
