Service Access to Volumes and Bind Mounts

directly into a container's writable layer. You should instead use data volumes or bind mounts. This principle also applies to services. You can create two types of mounts for services in a swarm, `volume` mounts or `bind` mounts. Regardless of which type of mount you use, configure it using the `--mount` flag when you create a service, or the `--mount-add` or `--mount-rm` flag when updating an existing service. The default is a data volume if you don't specify a type. #### Data volumes Data volumes are storage that exist independently of a container. The lifecycle of data volumes under swarm services is similar to that under containers. Volumes outlive tasks and services, so their removal must be managed separately. Volumes can be created before deploying a service, or if they don't exist on a particular host when a task is scheduled there, they are created automatically according to the volume specification on the service. To use existing data volumes with a service use the `--mount` flag: ```console $ docker service create \ --mount src=<VOLUME-NAME>,dst=<CONTAINER-PATH> \ --name myservice \ <IMAGE> ``` If a volume with the name `<VOLUME-NAME>` doesn't exist when a task is scheduled to a particular host, then one is created. The default volume driver is `local`. To use a different volume driver with this create-on-demand pattern, specify the driver and its options with the `--mount` flag: ```console $ docker service create \ --mount type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=<DRIVER>,volume-opt=<KEY0>=<VALUE0>,volume-opt=<KEY1>=<VALUE1> --name myservice \ <IMAGE> ``` For more information on how to create data volumes and the use of volume drivers, see [Use volumes](/manuals/engine/storage/volumes.md). #### Bind mounts Bind mounts are file system paths from the host where the scheduler deploys the container for the task. Docker mounts the path into the container. The file system path must exist before the swarm initializes the container for the task. The following examples show bind mount syntax: - To mount a read-write bind: ```console $ docker service create \ --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH> \ --name myservice \ <IMAGE> ``` - To mount a read-only bind: ```console $ docker service create \ --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH>,readonly \ --name myservice \ <IMAGE> ``` > [!IMPORTANT] > > Bind mounts can be useful but they can also cause problems. In > most cases, it is recommended that you architect your application such that

This section discusses how to give a Docker service access to volumes or bind mounts, emphasizing the importance of using these over writing directly to a container's writable layer. It details the creation and usage of both data volumes and bind mounts within a swarm service, including examples of creating services with these mounts using the `--mount` flag. The use of existing data volumes, specifying volume drivers, and read-only bind mounts are also covered.