I'm having a bit of trouble understanding the differences between two ways to define volumes in Docker Compose:
1. Using a bind mount like this:
```yaml
services:
servicename:
image:
volumes:
- ./subdirectory:/path/to/container/directory
```
2. Using a named volume like this:
```yaml
services:
servicename:
image:
volumes:
- volumename:/path/to/container/directory
volumes:
volumename:
```
What makes one approach necessary in certain configurations? For example, when I tried using it with WordPress, it only accepted the second version. Any insights would be greatly appreciated!
4 Answers
The main difference is that using `./subdirectory:/path/to/container` is a bind mount, while `volumename:/path/to/container/directory` is a volume mount. Bind mounts are tied to the host's filesystem directly, but volumes are managed by Docker.
If you're using named volumes, you can utilize volume drivers to connect to external file servers, which offers more flexibility. Also, named volumes can be preloaded with data from the image, unlike bind mounts that don’t have this feature.
When you bind-mount, permissions are up to you to handle, but Docker automatically handles permissions for volumes, which can save some headache. If you're looking for persistent data storage across container restarts, volumes are usually the way to go.
Using named volumes allows Docker to manage your storage without you having to worry about where the data is physically located, which can simplify things, especially in larger setups.
Check out the Docker documentation on bind mounts and volume mounts for more details. They explain the pros and cons, and how to use them effectively based on your needs.
This is the exact kind of answer I was looking for. Very much appreciated!