A small utility waiting for services linked to a Docker container being ready.
First, install the utility into your image by adding this to your Dockerfile:
RUN curl --location --silent --show-error --fail \
https://github.com/Barzahlen/waitforservices/releases/download/v0.6/waitforservices \
> /usr/local/bin/waitforservices && \
chmod +x /usr/local/bin/waitforservices
There's also a Makefile in this repository if you want to build the binary yourself.
Then, during container startup, you can use the waitforservices command to wait for all services being ready.
Without configuration, it finds all TCP services specified by the environement variable declared like __HOST and __PORT (for example POSTGRES_HOST and POSTGRES_PORT) and concurrently and repeatedly tries to open a TCP connection to all of them.
When the legacy option is specified, it finds all TCP services linked to a Docker container via their environment variables
When all connections are successful, it returns. If one or more services aren't ready within a specified timeout (60 seconds by default), it aborts and exits with status 1.
waitforservices also supports waiting for an HTTP request to / to return a response.
$ ./waitforservice -help
Usage of ./waitforservices:
-httpport int wait for an http request if target port is given port
-ignoreport int don't wait for services on this port to be up
-legacy use docker link enviroment variables
-timeout int time to wait for all services to be up (seconds) (default 60)
Attempt to connect to all TCP services linked by the environement variable
declared like _HOST and _PORT and wait for them to accept a TCP connection.
When the _legacy_ option is specified, it finds all TCP services linked to
a Docker container via their environment variables.
When an <httpport> is specified, for services running on <httpport>, after
a successful TCP connect, do an HTTP request and wait until it's done. This
is useful for slow-starting services that only start up when they receive
their first request.
When timeout is over and TCP connect or HTTP request were unsucecssful, exit
with status 1.
When starting multiple Docker containers at once with containers depending on and linking to other containers (e.g. using docker compose), you might want to do some initalization in one container depending on a service in another container already running. E.g. a web application running database migrations on startup (for testing) might need a database service in a separate container to be running, but the database container might need a few seconds until it's started and ready for connections.
In your container startup script, waitforservices allows you to wait for other services to be ready by repeatedly trying to open a TCP connection to all linked services and blocking until it succeeds or times out.
We wrote a blog post explaining why we built waitforservices how we use it.
waitforservices' options are pretty limited at the moment (e.g. the -httpport and -ignoreport parameters could support multiple ports), so we'd be happy if you create pull requests or report issues.
waitforservices is licensed under MIT.