Utility waiting for linked services in a Docker container being ready
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README.md

waitforservices Travis CI Status

A small utility waiting for services linked to a Docker container being ready.

NOTE: Docker link environment variables are deprecated and will be removed. We haven't thought about how waitforservices will work then. See issue 3 for more information. We'd be happy about ideas.

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.

Installation

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/v0.5/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.

Usage

Without configuration, it finds all TCP services linked to a Docker container via their environment variables and concurrently and repeatedly tries to open a TCP connection to all of them.

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=0: wait for an http request if target port is given port
  -ignoreport=0: don't wait for services on this port to be up
  -timeout=60: time to wait for all services to be up (seconds)

Attempt to connect to all TCP services linked to a Docker container (found
via their env vars) and wait for them to accept a TCP connection.

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.

Contributions

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.

License

waitforservices is licensed under MIT.