Improve logging for HikariCheckpointRestoreLifecycle

[deki]

Adressing #42906, open to change it to an exception instead of the warning message as it won't work as expected without allow-pool-suspension=true.

[wilkinsona]

WDYT please, @christophstrobl and @sdeleuze?

[sdeleuze]

Will the warning be also printed when doing a regular shutdown of the application?

[wilkinsona]

Yes, I believe so. If org.crac.Resource is on the classpath then HikariCheckpointRestoreLifecycle will be auto-configured. The log message will then be output irrespective of the type of shutdown that's being performed.

[christophstrobl]

Adding the shutdown time is a nice addition, though I think it should be formatted with a reasonable time unit.
Not so sure about the warning log message for suspension. Thought the requirement for pool suspension had been documented/is easy to find.

[deki]

I don't see it in https://docs.spring.io/spring-boot/reference/packaging/checkpoint-restore.html, where could I have read about it?
I think as long as crac is on classpath, users will consider using checkpoints at some point and the warning message would point them in the right direction.

[christophstrobl]

the link in the docs seem to be broken.

... resources such as socket, files and thread pools on a limited scope.

...so the info is not as easy to be found as I had assumed.

[wilkinsona]

#42938 should have fixed the link to the status page.