This is the last remaining blocker to switching to a Toolforge Build Service container for the tool. We want to preserve the ability to update the channel mappings for both Phorge and Gerrit without restarting those tasks. We also want to preserve tracking of who changed the config and when.

Today runtime config updates work by having a post-merge job call a web hook running in the tool's namespace. That web hook executes git pull in the $HOME/wikibugs2 git repo. This puts the latest config on the $HOME NFS share. The wikibugs2 irc and wikibugs2 gerrit tasks both use the wikibugs2.channelfilter.ChannelFilter.update() method to check for updated file mtime on their YAML config files and reload configuration from disk when the mtime has changed since the last (re)load.

I've had several different ideas about how to replace the git + mtime check mechanism. Loading data from Redis in the tasks with some external service responsible for updating the Redis data is likely the simplest change using the existing tech stack for the tool. A slight twist on that solution would be for the external service to also act as the configuration provider to the jobs instead of using Redis to pass state. This would avoid adding new Redis dependencies which seems prudent in light of T360596: Figure out a plan to move forward with regarding Redis License changes.

I'm leaning towards a design that would introduce a new python webservice to the tool. Initially the webservice would be responsible for providing API endpoints for:

• Fetching the stored Gerrit channel configuration (used by the Gerrit task)
• Fetching the stored Phorge channel configuration (used by the IRC task)
• Handling the web hook callback from GitLab to trigger an update of the stored configuration

The webservice could load the configuration from the GitLab repo via http both as a bootstrap when initially starting and in response to a thunk of the web hook.

To avoid the complexity of needing separate API endpoints to check if the configuration had changed, the webservice should support Etag+If-None-Match or more simply a query string param so the client can request the config only if it has changed from a prior known state. The server should respond with a 304 Not Modified status and no body when the provided config identity is unchanged.

wikibugs2.channelfilter.ChannelFilter should support both loading config directly from disk for ease of testing and development as well as the config server solution. The direct loading configuration does not need to support automatic reloading.