Waiting for containers in Docker Compose

When I first started using Docker Compose I attempted to use the depends_on functionality thinking that it would properly wait for other containers to start. After reading the documentation further I found this this was not the case and I was left wondering how to orchestrate the startup order of services that depends on other containers.

Dockerize

After looking at a number of scripts I settled on using jwilder/Dockerize due to it being east to install in containers and its syntax. It allows you to wait for services based on a number of different protocols which helps when you need to wait for servers, databases, or even files to be available.

Using Dockerize

The README of jwilder/Dockerize has just about everything you need to get started. It even has its own Docker container that you can extend from. I prefer to simply include the following in my test containers.

ENV DOCKERIZE_VERSION v0.6.1
RUN wget https://github.com/jwilder/dockerize/releases/download/$DOCKERIZE_VERSION/dockerize-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
    && tar -C /usr/local/bin -xzvf dockerize-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
    && rm dockerize-linux-amd64-$DOCKERIZE_VERSION.tar.gz

With this in my test container I can then utilize the dockerize command to wait for services. If I want to wait for an http service I might do something like the following.

dockerize -wait tcp://api-server:8080 -timeout 1m

When I want to wait on a database container such as mysql I use the following command.

dockerize -wait tcp://mysql:3306 -timeout 1m

Note the hostnames I use in the above commands are the names I specify when I setup the containers within the Docker Compose configuration files.