Waiting for initialisation completed

[raphaelcoeffic]

For some integration tests, I would need to be able to wait for container initialisation to be fully completed. The framework instrumenting the container needs this to be able to start a series of tests.

Unfortunately, I cannot rely on the service itself, as it may or may not be up, depending on configuration, so that I cannot for open ports or any other type of side-effects.

Ideally, the service I'd want to wait for is a oneshot, so that I cannot even use polling together with s6-svstat or readiness notification. Alternatively, being to check if s6-rc has completed init successfully would help.

Is there any other alternative to poll/wait for a oneshot to be up? In my case, that would be done from outside the container using something similar to docker exec.

[skarnet]

The natural notification for "the initialization has completed" is just "s6-rc exits 0", but it's true that there's currently no hook in rc.init to notify external programs that it's the case. If there's demand, I can probably add one in the future.

For now, your best bet is probably to add a oneshot that depends on top. Do not add that oneshot to any bundle, that would create a dependency loop and make your initialization fail.

In that oneshot, run whatever notification mechanism you want - write to a file, to a pipe, whatever. Make sure it doesn't block if your external program that needs the notification isn't present.

Since the oneshot depends on top, which is the bundle that s6-rc brings up at container initialization time, it will only run once everything else is up, which is the synchronization you want.