Temporal Fun

This repo shows you some fun with temporal, running a workflow under temporal, but having the bulk of the work done by an external REST API that calls back when work is done.

The setup

• You have an external system calling your API (say, a webhook that fires when new PRs are open). This is handled by the go worker's pr http handler.
• Once the API is called, it enqueues a workflow run to deal with PRs. This is put in termporal.
• worker process picks up this workflow run, and calls out to a leaf process that does the work. this is the node.js process in the leaf dir.
• The leaf worker gets a callback url. When it's done (after 10 seconds) it calls back to complete the work.
• The worker waits for two such jobs running in parallel, then does some extra work internally, then does some further external work (say, to set a commit status on the original PR). Then its done!

Temporal handles:

• queueing and limiting the work after accepting that original /pr call
• checkpointing steps in the workflow (in workflow/workflow.go) so that in the event of failure, work is not lost.
• retries for any part of originally sending the work to the leaf, or if it does not call back (or heartbeat) before a dealine.

Run it

• Run docker compose up -d to start temporal and the local services:
  • worker, the workflow runner and rest API
  • leaf, a leaf capability service

Now you're ready to enqueue work.

• install httpie because it's really good and you deserve nice things. you do. it's ok to indulge once in a while in a nice CLI tool.
• Set up some work! run http POST 127.0.0.1:6007/pr repo=jbowes/repl pr=123 old=bahbah new=naynay To simulate a PR against the jbowes/repl repo, with old and new SHASUMs.
• Watch the output for the leaf process, as it gets requests, and sends completion information after 10 seconds.
• Watch the worker process as it finishes jobs and tells you that it set a commit status.
• Turn things off and on again and have fun.