Testcontainers ; Running @Testcontainers Tests inside docker [Running Docker inside Docker]

Question

How To Run @Testcontainers based test cases inside the docker container ?

I have Simple Spring Boot App that has Integration Test (Component level) that are interacting with containers using Testcontainers. Test cases are ruining fine from outside container(Local machine).

We are running everything in containers and build is running on docker jenkins image. Docker file is creating jar and then image. @Testcontainers is not able to find docker installed. Below is my docker file.

FROM maven:3.6-jdk-11-openj9
VOLUME ["/var/run/docker.sock"]
RUN apt-get update
RUN apt-get -y install docker.io
COPY . /usr/src/app
WORKDIR /usr/src/app
RUN mvn -Dmaven.repo.local=/root/m2 --batch-mode -f pom.xml clean package
EXPOSE 8080
CMD ["/bin/bash"]

While running build i am getting below below error

org.testcontainers.dockerclient.EnvironmentAndSystemPropertyClientProviderStrategy - ping failed with configuration Environment variables, system properties and defaults. Resolved dockerHost=unix:///var/run/docker.sock due to org.rnorth.ducttape.TimeoutException: Timeout waiting for result with exception

Whats the best way to handle this case ? I want to run my component level integration test during mvn build phase using docker file.

below reference did not helped me. https://www.testcontainers.org/supported_docker_environment/continuous_integration/dind_patterns/

Answer 1

This is not complete answer but you should enable access to a docker daemon from inside your container. Installing Docker and running it's daemon inside your container is complicated so not recommended. Docker can be controlled via Unix socket or over TCP (I assume the host system is a Linux).

How Test containers look for Docker: By default it tries to connect to Unix socket /var/run/docker.sock. You can specify other socket path or TCP address by setting environment variables (DOCKER_HOST).

How docker exposes it's control API: By default via Unix socket /var/run/docker.sock (on your host). You can expose docker API elsewhere by adding following parameters to docker start command (the location of command launching your docker is system dependent): -H fd:// -H tcp://127.0.0.1:2376. Note that you can specify more than one option. -H fd:// - is the default, tcp://127.0.0.1:2376 - tells Docker to listen on localhost port 2376.

How to make Docker available inside your container ("Docker in Docker"): If you enabled network access - no need to do additional config except pointing Testcontaners to it as mentioned above. If you want to use default Unix socket then you can map (mount) it into container via volume option:

docker run --volume /var/run/docker.sock:/var/run/docker.sock your-image-id-here

The remaining problem is that mounted docker.sock inside container will also be owned by root:docker (with same uid:gid as on your host system) so Testcontainers would work only if your container user can connect to that socket. That is user of running process is root or happen to have exact same group id inside your container as group id of docker on your host system. I do not know yet a good solution to this one, so for starters you can run your tests inside container as root, or hard-code container's user group-id to match your host's docker group id.