wait-for-it

wait-for-it.sh is a pure bash script that will wait on the availability of a host and TCP port. It is useful for synchronizing the spin-up of interdependent services, such as linked docker containers. Since it is a pure bash script, it does not have any external dependencies.

Usage

wait-for-it.sh host:port [-s] [-t timeout] [-- command args]
-h HOST | --host=HOST       Host or IP under test
-p PORT | --port=PORT       TCP port under test
                            Alternatively, you specify the host and port as host:port
-s | --strict               Only execute subcommand if the test succeeds
-q | --quiet                Don't output any status messages
-t TIMEOUT | --timeout=TIMEOUT
                            Timeout in seconds, zero for no timeout
-- COMMAND ARGS             Execute command with args after the test finishes

Examples

For example, let's test to see if we can access port 80 on www.google.com, and if it is available, echo the message google is up.

$ ./wait-for-it.sh www.google.com:80 -- echo "google is up"
wait-for-it.sh: waiting 15 seconds for www.google.com:80
wait-for-it.sh: www.google.com:80 is available after 0 seconds
google is up

You can set your own timeout with the -t or --timeout= option. Setting the timeout value to 0 will disable the timeout:

$ ./wait-for-it.sh -t 0 www.google.com:80 -- echo "google is up"
wait-for-it.sh: waiting for www.google.com:80 without a timeout
wait-for-it.sh: www.google.com:80 is available after 0 seconds
google is up

The subcommand will be executed regardless if the service is up or not. If you wish to execute the subcommand only if the service is up, add the --strict argument. In this example, we will test port 81 on www.google.com which will fail:

$ ./wait-for-it.sh www.google.com:81 --timeout=1 --strict -- echo "google is up"
wait-for-it.sh: waiting 1 seconds for www.google.com:81
wait-for-it.sh: timeout occurred after waiting 1 seconds for www.google.com:81
wait-for-it.sh: strict mode, refusing to execute subprocess

If you don't want to execute a subcommand, leave off the -- argument. This way, you can test the exit condition of wait-for-it.sh in your own scripts, and determine how to proceed:

$ ./wait-for-it.sh www.google.com:80
wait-for-it.sh: waiting 15 seconds for www.google.com:80
wait-for-it.sh: www.google.com:80 is available after 0 seconds
$ echo $?
0
$ ./wait-for-it.sh www.google.com:81
wait-for-it.sh: waiting 15 seconds for www.google.com:81
wait-for-it.sh: timeout occurred after waiting 15 seconds for www.google.com:81
$ echo $?
124