![]() The question of running Docker in a Docker container occurs frequently when using CI/CD tools like Jenkins. However, complete encapsulation is actually not needed for most use cases, and this workaround is a legitimate solution whenever you need to use Docker inside a Docker container.īut when do you need to use Docker within a Docker container anyway? When do you need it? You might think that it would be nice if the Docker installation inside the container was completely encapsulated from the host system. And if you run a container inside the container, this container will actually be a “sibling” to all the containers running on the host machine (including the container in which you are running Docker). This means, if you pull an image inside the container, this image will also be visible on the host system (and vice versa). This is because we wired up the Docker CLI in the container to talk to the Docker daemon that is already running on the host system. It looks like the Docker installation of the container that you just started, and that you maybe would expect to be fresh and untouched, already has some images cached and some containers running. The output is exactly the same as when you run these commands on the host system. To achieve this, you can start a Docker container, that has Docker installed, with the following bind mount option: -v /var/run/docker.sock:/var/run/docker.sockįor example, you can use the docker image, which is a Docker image that has Docker installed, and start it like this: docker run -ti -v /var/run/docker.sock:/var/run/docker.sock dockerĪnd then inside the Docker container that you just started, run some Docker commands, for example: docker images docker ps At any time, there is only one Docker daemon running in your machine, the one running on the host system. That means, you will have a Docker CLI in the container, as well as on the host system, but they both connect to one and the same Docker daemon. With this approach, a container, with Docker installed, does not run its own Docker daemon, but connects to the Docker daemon of the host system. The good news is that there is another, recommended, way to use Docker inside a Docker container, with which the two Docker instances are not independent from each other, but which bypasses these problems. The answer is yes, but it is not recommended because it causes many low-level technical problems, which have to do with the way Docker is implemented on the operating system, and which are explained in detail in Jérôme Petazzoni’s post. The question that this article looks at is the following: if you run a Docker container that has itself Docker installed, can you then run Docker inside that Docker container (for example, to pull and build images, or to run other containers) with the two Docker instances being completely independent from each other? ![]()
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