New next.js instance regenerates shared cache

[TimGeudens]

Summary

We are self-hosting a next.js app using app router. We have a shared disk where all instances run from. Since we use the default next.js cache it is also used for reading and writing the fetch cache and full route cache.

However we noticed that the full route cache files (.html, .meta & .rsc) are constantly regenerated. This happens every 3-10 minutes.
After doing some testing locally we noticed that a new server instance will regenerate those files no matter what.
On production when an instance restarts or when it is added by automatic scaling, this triggers a regeneration of full route files for all requests on that new instance. As a result we get quite some disk writes which we did not expect. The fetch cache however seems fine since rebuilding the page is still pretty fast.

We also tried adding a Redis cache handler but saw the same issue there (cache string gets updated when new instance comes online).

We also tried adding the build id in the config when testing locally but that did not help either.
generateBuildId: async () => { return 'build-1'; }, deploymentId: 'build-1',

Is this something that is expected or is there something we could change so that new instances just read from the existing cache?

Additional information

Some more info about the app: we have one catch-all route (next to some fixes routes) that generates 98% of the pages. 
We added this to enable ISR:
`export const dynamicParams = true;
export const generateStaticParams = async () => [];`

We disabled memory cache in config with
`  cacheMaxMemorySize: 0
`

Then we just ran multiple instances like this:
`    "start": "next start -p 3003",
    "start2": "next start -p 3004",
    "start3": "next start -p 3005",`

You can check the timestamp of the generated .html file in .next/server/app/your-page.html and you can see the date changes when restarting an instance and visiting /your-page.

Example

No response

[wgbx]

I have the same problem, is there a better plan? Thank you