Introduce `--wait` or `--watch` capabilities to **`depends_on`**, avoiding configuration of healthchecks for simple use cases

[esauvisky]

Description

Sometimes, we need to wait a bit after launching a container before starting a container that relies on it, as services may take time to boot up. The proper approach is to set a healthcheck and use that as the sign that the dependency is genuinely ready for the dependent service to start. However, healthchecks can be quite complicated and hard to implement in every case, making it much easier if we could just pause for a few seconds before starting the dependent service.

With the introduction of the (relatively) new features --wait and --watch, I propose we expand their capabilities to include the depends_on feature.

[tchavei]

Indeed that would be a excellent quality of life improvement. I have several containers that "depend on" other containers but sometimes they still start too quickly before the preceding container finishes loading the app. A timer or delay would be invaluable.

Great idea!

[ndeloof]

they still start too quickly before the preceding container finishes loading the app

This is exactly what healthcheck is about. Sounds pretty easy to configure a healthcheck to run curl localhost... waiting for app to return a 200 HTTP result

healthchecks can be quite complicated and hard to implement in every case, making it much easier if we could just pause for a few seconds before starting the dependent service.

Sounds to me this proposal is a bad workaround for such a situation. Writing a basic healthcheck script should not be that hard, do you have any example in mind?