Replace setInterval

[fcaps]

using setInterval can be a huge issue described in multiple articles.
just search "nodejs why setInterval is bad".
a common solution is something like https://www.npmjs.com/package/node-cron, or everything that is based on https://nodejs.org/api/events.html#class-eventemitter

[fcaps]

this issue is more critical than thought, i forgot to shutdown my pc (and containers) for multiple hours, and the container was doing weird stuff.

steps to reproduce:

• start the container
• maybe kill the wordpress instance, so it will create issues
• let it run for some time (depends on your system)
• try to stop it -> not responsive
• kill it -> killed, but somehow not correctly
• start the same container again -> not starting
• wait some time
• start it again -> working

Since the website also has issues on prod where we cannot start it after a crash, i guess it's not a local issue.

I would guess it's all the setInterval creating a memory/thread mess, but could be wrong.

[fcaps]

update:
looking into this even more, i suspect having a "real" cache mechanism is even more useful than just updating a file every x mins.

old:
server starts -> query endpoints of wp/java-api -> saves file on local disk

new:

browser hits endpoint  ->
   -> cache is not stale -> deliver 
   -> cache is stale -> query endpoint -> safe cache -> deliver

Some upside with this approach:

• no need to have a cronjob running on the server (no setInterval/timeout)
• container can start without calling endpoints on java-api/wordpress
• no calls if there is no need to update (if there is no user)

downsides:

• one user is the "cache-looser" (long http request time)
• need a mutex/flock to not call the endpoint multiple times if cache is stale
• some may complain about memory usage (<10MB)
• some may complain about no file to look at
• maybe more

packages that can be used:

https://github.com/node-cache/node-cache
maybe a mutex? but have to check it => https://stackoverflow.com/questions/64899813/does-node-cache-uses-locks