59 lines
2 KiB
Markdown
59 lines
2 KiB
Markdown
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# Docker storage
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The following problems related to storage face containerized environments:
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- Container storage is ephemeral. When the container is removed the read-write layer is removed. How can we persist data?
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- Container storage is isolated: containers cannot access each other's file systems. If they need to share data, this could be a problem
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### Docker volumes
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Docker volumes are the solution to this. Volumes:
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- store data on the host file system (i.e. outside the container)
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- persist data beyond the lifecycle of the container
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> A Docker volume is a logical volume that exists outside the container file
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> system. It maps to a directory on the host and this location is managed by Docker - not much control over this.
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Can be named or anonymous. Anonymous vols are created by Docker as needed. Named come from the user.
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Volumes can be **named** or **anonymous**. Anonymous volumes are created by Docker as needed. Named volumes are named by the user. In both cases Docker decides where to create the volume.
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### Creating a volume
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```sh
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docker run -d -rm -v /usr/share/nginx/html nginx:latest
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```
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The `-v` flag indicates volume. The file reference is the mount point _within_ the container. This is how the persistent storage it will appear. The _actual_ volume exists outside of the container anonymously in a place decided by Docker.
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To create a named volume you first have to create:
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```
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docker volume create volume_name
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```
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Then you can designate it:
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```
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docker run -d -rm -v volume_name:/usr/share/nginx/html nginx:latest
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```
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The actual location is still hidden and decided by Docker.
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As these are anonymous they will show ups as GUIDs in the volume viewer in Docker Desktop:
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// TODO: add screenshot
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### Commands
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```
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docker volume ls
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docker volume rm
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docker volume inspect
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docker volume prune // remove all unused volumes
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```
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Inspect is only really informative if you are on Linux because it will show you the actual physical path. With Windows and Mac the referernce is to a virtual machine.
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