wait is a really small (<5MB) Docker utility that blocks until another container is accepting TCP connections, and errors-out if it cannot connect within a given timeout. It can be used to ensure that a service is up and running before starting another service that depends on it.

The default operation looks up all the EXPOSEd ports of all the linked containers and waits for them

$ docker run -d --name mycontainer some-image-or-other
$ docker run --link mycontainer:mycontainer --rm martin/wait
Waiting for 172.17.0.105:5432  .  up!
Everything is up

It doesn't matter what the link alias is.

If you want to wait for only a subset of the ports in a linked container, you can provide the list with the -p parameter:

$ docker run -d --name mycontainer some-image-or-other
$ docker run --link mycontainer:mycontainer --rm martin/wait -p 5432
Not checking 172.17.0.105:6379 because port is not included.
Waiting for 172.17.0.105:5432  .  up!
Everything is up

If you want to connect to hosts/ports that haven't been linked by Docker, you can provide the list with the -c parameter:

$ docker run --rm martin/wait -c 8.8.8.8:53,github.com:443
Waiting for 8.8.8.8:53  .  up!
Waiting for github.com:443  .  up!
Everything is up

By default each connection attempt will bail after 30 seconds. You can override this with -t parameter:

$ docker run martin/wait -c github.com:5432 -t 15
Waiting for github.com:5432  ...............................  ERROR: unable to connect

If any connection times out, the wait container immediately exits with status code 1

credits

waisbrot/wait: https://github.com/waisbrot/docker-wait n3llyb0y/wait: https://github.com/n3llyb0y/docker-wait aanand/wait: https://github.com/aanand/docker-wait