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.

NOTE: as of Docker v29.0 the default operation and the -p parameter are no longer functional, you have to use the -c parameter.

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