GitHub webhook support

[g4s8]

Feature request: add configuration to listen for GitHub webhooks instead of timer, when somebody make a change in GitHub repository, it calls pod's endpoint and kube-applier updates changed files.

[oliverhausler]

@g4s8 This is the correct approach to the problem. Frequent pulls cause unnecessary network load and admin wait times.

[gregory-lyons]

Sorry for long delay in response!

One thing to keep in mind is that kube-applier only uses a local repo and assumes that something else is keeping the local copy in sync with a remote (e.g. a git-sync sidecar). kube-applier itself doesn't take any action (e.g. pull) to ensure its local copy is up to date - that task is sufficiently complex to warrant its own sidecar implementation. Leaning on the "do one thing" idea, I'd prefer not to bloat kube-applier by replicating the same logic.

Given that, I'm not sure a webhook approach is viable to build into kube-applier. If I push a commit to my remote and it triggers a kube-applier webhook, how can I ensure that kube-applier's local repo contains my new commit?

Perhaps there's some way that the webhook call could actually include the contents of changed file(s), but that doesn't feel like a practical approach. And you would still need a local copy of the repo anyway if you want the periodic "full runs" (which I find quite valuable).

I wonder if this might be a better feature request for git-sync, since that's the service that is actually doing pulls over the network.

General disclaimer that I'm open to changing my mind on any of the above.