Wait for service to start?

[alexandrosm]

Maestro has this feature whereby it waits for containers to actually be ready to accept connections before starting to launch others that depend on them. The implementation for that is here. This feels like a feature decking should have, especially considering the strong support for links.

[makeusabrew]

This is absolutely something I want to implement; hadn't thought about simply pinging the relevant port(s). It's already something I get caught out on when creating new clusters on a private project as MongoDB (with default config) takes an age to start up for the first time (e.g. on create - it's fine on subsequent calls to start).

A couple of random thoughts:

• Need to deal with containers which have more than one critical 'service' (granted the idea should be to only expose one, but have to allow for more)
• Need to support services whose readiness can't be detected simply by pinging a port, e.g. a data processor which does some start up logic before connecting to some queues.

Previously I'd considered something rather dirty in another project; allowing use of a pattern to grep for in stdout to check for a known 'ready' line (e.g. the data processor might log out "ready!" or whatever once it had started) and making that the ready precondition. Food for thought.

[alexandrosm]

I guess the endgame of this would be to have a hook with a JS function executed in some context that would test the container and return true if it's ready?

I do suspect there is value in a default like what maestro uses though.

[makeusabrew]

Yeah, something like that. And you're right; for now, simple TCP pings will cover 90% of use-cases.

[makeusabrew]

Fixed in 0.4.0 :)