[JonnieCache]

This is all well and good, but the devil is in the details. Like rdeboo says, what happens when you do need to change the datastore config? Databases famously need plenty of care and attention to achieve optimal performance. They are decidedly not fire and forget systems. How do I tweak my postgresql performance parameters in the immutable world?

[falcolas]

Not to mention the mere act of transferring data as part of the migration from old to new can take hours on its own.

[icebraining]

You could keep Postgres in an immutable image, with only /var/lib/postgres in a separate volume. Upgrading the PG config would just be a matter of unmounting it, replacing the image and re-mounting. (Docker automates this with its "data volumes", but you can do it manually too).

[wstrange]

In theory yes - but that strategy doesn't always work. Sometimes the implementation of the data store changes between releases - requiring an upgrade or data migration.

For large datasets that can take hours / days.

[icebraining]

That may prevent the simple unmount/replace image/mount workflow, but it doesn't prevent the separation between the mutable and immutable parts of the DBMS.