Mount filesystems again when rotating PHP runtime instance

[jeroenpf]

Fixes #516

Proposed Changes

When rotating an instance, the callback used by the rotation logic should prepare the filesystem and mount the required directories again as they are not retained. Only MEMFS mounts are carried over to the fresh instance but we are using NODEFS for most mounts.

To achieve this, i extracted some logic out of the huge main function startWPNow to make it reusable when creating the first instance AND during the rotation.

Not all logic needs to be executed again. We only care about the mounts and PHP settings.

Testing Instructions

• Create a site
• Run ab -n 500 http://localhost:<port>/
• Wait for the 500 requests to run and ensure there are no failing requests
• Keep an eye on the console where you ran npm start when request 400 has been reached, you should see a log output telling you the PHP instance is being rotated.
• Observe that you can navigate the WordPress site and WP-admin without issues

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[kozer]

Tested it and works as expected:

❯ ab -n 500 http://localhost:8885/


Benchmarking localhost (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests

Completed 500 requests
Finished 500 requests

[fluiddot]

LGTM 🎊 ! Great work @jeroenpf 🏅 ! I've confirmed that after 400 requests, the PHP instance was rotated and kept working.

I added a couple of comments but none shouldn't block the PR.