We don't really need to fail in such a spectactular way,
but it's probably good to do. It will only happen for people
who are defining their own user/group id, which is rare.

It seems like a good idea to tell them that this doesn't work
as they expect anymore and to ask them to remove these variables,
which otherwise give them a fake sense of hope.

Related to #486 (Github Pull Request).

If one runs the playbook with `--tags=setup-all`, it would have been
fine.

But running with a specific tag (e.g. `--tags=setup-riot-web`) would
have made that initialization be skipped, and the `matrix-riot-web` role
would fail, due to missing variables.

No migration steps should be required.

Should help with #300 (Github Issue).

This will not work yet, as no version of Riot currently supports it.
It's expected to land in riot-web v1.5.16 via matrix-org/matrix-react-sdk#4348.

https://github.com/matrix-org/matrix-doc/pull/1957

Yay Riot iOS now supports integration manager discovery!

Riot used to be fine with it being blank but now it complains. This creates an ugly looking comma when there is an identity server configured but I guess that's fine.

We've just updated it in the task above, so it's unnecessary

We've just updated it in the task above, so it's unnecessary

Since commit b9753635 the task 'Ensure docker-ce is installed (Debian)' fails with an error on CentOS although it should not even run on this OS.

With most people on Synapse v0.99+ and Synapse v1.0 now available,
we should no longer try to be backward compatible with Synapse 0.34,
because this just complicates the instructions for no good reason.

Use Jinja2 lstrip_blocks option in templates to ensure consistent
indentation in generated files.