Whether you end up with a volume or a bind mount, depends on which short syntax variation you use. Summing it upĭocker Compose allows you to configure volumes by using a short syntax string. The official docs have a section about volumes vs bind mounts that explains the differences between the two in more detail. Bind mounts are specific to the host system and Docker doesn't manage them. are relative to the location of docker-compose.yml.īind mounts are discouraged for database containers since that makes them less portable. If source is a path, absolute or relative, Docker Compose will bind mount the folder into the container. Bind mounts don't have a name and they can't be named. Top-level volumes key always declares volumes, never bind mounts. This volume needs to be declared in the same file in the top-level volumes key declaration. If a source is present and it's not a path, then Docker Compose assumes you're referring to a named volume. The directory's path on the host system is by default /var/lib/docker/volumes//_data, where is a random ID assigned to the volume as its name.

When only a target is specified, without a source, Docker Compose will create an anonymous directory and mount it as a volume to the target path inside the container. Docker Compose is smart about recognising which variety is used and whether to use a volume or bind mount. This optionality leads to three unique variations you can use to configure a container's volumes. MODE is a mount option which can be read-only or read-write. TARGET is an absolute path in the container. SOURCE can be a named volume or a (relative or absolute) path on the host system. The volume configuration has a short syntax format that is defined as: This configuration has a short (and a long) syntax format. That's where you configure volumes for a specific service/container such as a database or web server. In this article, we'll talk about the nested volumes key. Declares volumes which can be referenced from multiple services. Configures volumes for a particular service. In docker-compose.yml, the volumes key can appear in two different places. Two volumes keys in docker-compose.ymlīefore we talk about the different ways to specify volumes, let's first clarify which volumes key we're referring to. I list and explain them in this article below. The different variations are essentially three unique forms. You'll simply know by looking at the syntax whether a volume or a bind mount is used behind the scenes. I wrote this article so that next time you read a Docker Compose file, you won't have to guess anymore. Whenever I had to read a docker-compose.yml file, I had to look up the official documentation or run a quick local experiment to figure out how Docker Compose would mount the directories into the container.

Which of these are volumes and which are a bind mounts? Docker Compose allows you to configure volumes and bind mounts using a short syntax.

Docker compose volumes