Podman is a nice tool, that simplifies running rootless containers without the need for a separate, rootful daemon. One of the tools that you might miss when migrating from Docker to Podman is Docker Compose, which provides an easy-to-use, declarative approach to running and orchestrating containers.<\/p>\n\n\n\n
Since the Podman API is compatible with the Docker API, we can use Docker Compose with Podman, with the Podman API simply pretending to be the Docker API when called by Docker Compose. This post shows you how you can get started.<\/p>\n\n\n\n\n\n\n\n
On the host, you need three things: Podman, Docker Compose, and a non-root user. Everything else we need for running this example can be found in the Github repository https:\/\/github.com\/clemens-zauchner\/podman-with-docker-compose<\/a>.<\/p>\n\n\n\n In this post it is assumed that you have a system user set up already, Podman installed and Docker NOT installed. It is recommended to use a Podman version 4, which ships with RHEL. Furthermore, the code snippets below are assumed to be run as the non-root (system) user.<\/p>\n\n\n\n You can download the latest version of Docker Compose directly from Github. In this case, we will simply save the binary in the home directory of the non-root user and run it from there. (If the directory $HOME\/bin<\/em> does not exist, create it or modify the code below with a directory of your choice.)<\/p>\n\n\n\n Note<\/strong>: if you are using a system account, you need to export the XDG_RUNTIME_DIR<\/em> to prevent the error Failed to connect to bus: No medium found<\/em> in the next step. You can start the rootless Podman API socket via a predefined systemd service using:<\/p>\n\n\n\n You need to tell Docker Compose where to find the socket, so it can make API calls. Cannot connect to the Docker daemon at unix:\/\/\/var\/run\/docker.sock. Is the docker daemon running?<\/em><\/p>\n\n\n\n You can fix it by setting the DOCKER_HOST environment variable:<\/p>\n\n\n\n Now let’s have a closer look at the files in our example repository<\/a>. (If you haven’t already cloned the repo and you want to follow along, do it now.)<\/p>\n\n\n\n The declarations that Docker Compose interprets can be found in docker-compose.xml<\/a><\/em>:<\/p>\n\n\n\n We specify one service, called “flask”. For the corresponding container image, the build context is the current directory (“.”). We also specify to expose the port 5000 on the host, so we can reach the service from the host via curl<\/em> (once the container image has been built and the container is up and running).<\/p>\n\n\n\n You can build the image using docker-compose build<\/em>. The build tool for Podman is usually Buildah<\/a>, but if you use Docker Compose, a BuildKit<\/a> container is started (however, via the Podman socket, i.e. with Podman as container engine!) and builds the image, as declared in the Dockerfile<\/a> of our repository.<\/p>\n\n\n\n When you look at the output of podman ps<\/em> right after starting the build process, you can see a container buildx_buildkit_default<\/em> running. This is the container that builds the image.<\/p>\n\n\n\nPrerequisites<\/h3>\n\n\n\n
Installing Docker Compose<\/h3>\n\n\n\n
wget https:\/\/github.com\/docker\/compose\/releases\/latest\/download\/docker-compose-linux-$(uname -m) -O $HOME\/bin\/docker-compose\n\n$HOME\/bin\/docker-compose\nchmod +x $HOME\/bin\/docker-compose\nexport PATH=\"\/home\/$USER\/bin:$PATH\"<\/code><\/pre>\n\n\n\nStarting the Podman API socket<\/h3>\n\n\n\n
<\/em><\/p>\n\n\n\nexport XDG_RUNTIME_DIR=\"\/run\/user\/$(id -u)\"<\/code><\/pre>\n\n\n\nsystemctl --user start podman.socket<\/code><\/pre>\n\n\n\nSetting the DOCKER_HOST<\/h3>\n\n\n\n
If you skip this step (and don’t have Docker installed, as we assume), you will get an error like this:<\/p>\n\n\n\nexport DOCKER_HOST=\"unix:\/\/\/run\/user\/$(id -u)\/podman\/podman.sock\"<\/code><\/pre>\n\n\n\nThe example application<\/h2>\n\n\n\n
version: \"3\"\nservices:\n flask:\n build: .\n ports:\n - 5000:5000<\/code><\/pre>\n\n\n\nBuilding the image<\/h3>\n\n\n\n
Starting and stopping the containers<\/h3>\n\n\n\n