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Persistent Storage

Objective

  • Run a container that retains files it creates after a reboot.

To-do

  • Run docker run -it ubuntu bash, and inside the container:
    • Run touch /root/hello.txt.
    • Run ls /root/, and observe the file we just created exists.
    • Run exit to exit the container.
  • Run docker run -it ubuntu bash, and inside the container:
    • Run ls /root/, and observe our file no longer exists.
    • This is because containers are read only, and will clear all files that have been written to will be lost once the container stops running.
    • Run exit.
  • Next we will allocate a named volume to the container, so we can have persistent storage across containers.
  • Run docker run -it -v testvolume:/root/ ubuntu bash, and inside the container:
    • Run touch /root/hello.txt.
    • Run ls /root/.
    • Run exit.
  • Run docker run -it -v testvolume:/root/ ubuntu bash, and inside the container:
    • Run ls /root/, and observe this time our file still remains there. This is because we mount a named volume on top of the /root/ folder while booting the container, so anything written to that directory will be actually written on the named volume.
    • Run exit.

Gotchas

  • On windows, the container target path when mounting might need prefixing with another / like so: -v testvolume://root/.

Extra

  • Mounting a volume to a container overrides the contents of the target path inside the container.
  • Multiple containers can use the same volume at the same time. This can be useful for example if one container builds static files and another serves the compiled files.

Expected output

root@346745de2804:/# touch /root/hello.txt
root@346745de2804:/# ls /root
hello.txt
root@346745de2804:/# exit
exit

$ docker run -it ubuntu bash
root@65708aab62eb:/# ls /root/
root@65708aab62eb:/# exit
exit

$ docker run -it -v testvolume:/root/ ubuntu bash
root@f4358417b75b:/# touch /root/hello.txt
root@f4358417b75b:/# ls /root/
hello.txt
root@f4358417b75b:/# exit
exit

$ docker run -it -v testvolume:/root/ ubuntu bash
root@1d22d6ba4c97:/# ls /root/
hello.txt
root@1d22d6ba4c97:/# exit
exit

Up next

07 - Cleanup