Allow an app to start when its DataSource is unable to connect to the DB

[dsyer]

As long as this doesn't make the code too complicated (possibly it can be done with AOP which is clean), I would say a retry would be best practice for 12factor apps - you shouldn't rely on the database being available on startup, but you can assume that it will come back eventually up to a point.

There are probably other places we could do this, but you have to start somewhere. For reference, we have an optional retry (driven by classpath) in spring-cloud-config for the config client connection to the config server. It's a similar issue.

[wilkinsona]

Another place: if you're using Spring Session backed by Redis, the app fails to start when Redis is down

[jelmo]

+1

[dsyer]

We decided we can prototype something based on the Spring Cloud config client code: it's opt in, and also only on if spring-retry is on the classpath. In that case if a slow connection fails we back off and wait. The Spring application context will delay startup, but that's probably better (more robust) than just failing. Essentially this is most useful at development time because in production there should be an external agent (docker compose, a PaaS, supervisord, monit, etc.) that restarts a failed process, so the cleanest thing to do is fail as fast as possible. So maybe the retry behaviour should be on by default if devtools are on, and off otherwise.

[singram]

+1
Defaults sound reasonable with option to override.