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Running Docker Containers With A Shared Host File System (Docker Volumes Introduction)

In this lecture you're going to see how easy it is to map files into the container from your host filesystem.

Docker-Performance on a Mac

On Macs the performance of file shares is pretty low. If you have multiple thousand files to share, it can deteriorate and be 60x slower than WSL on windows or native Linux.

If you experience this, there is a new tool which you can try: http://docker-sync.io

Furthermore, there is a great overview about this issue on this blog, which also recommends looking into VirtioFS: https://www.proudcommerce.com/devops/docker-performance-on-apple-macbook-pro-with-m1-max-processor-status-and-tips

Video Walkthrough

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Steps and Explanations

Let's share some files from our host to our docker container. This is done with the "-v" flag and then "host-directory:container-directory" and is directly mapped into the container.

docker run --rm -v ${PWD}:/myvol ubuntu /bin/bash -c "ls -lha > /myvol/myfile.txt"
  • This command runs "ls -lha" and pipes the output to /myvol/myfile.txt
  • /myvol is "mounted" to the current working directory on the host
  • On the host you can observe a new file called "myfile.txt" with the output of "ls -lha"
  • The container is then ended and removed because of "--rm"

Using RAR without installing anything through Docker

From Docker-Hub I get an image that contains the rar tool. It's minimal, but it demonstrates what can be done with separated environments:

https://hub.docker.com/r/klutchell/rar/dockerfile

docker run --rm klutchell/rar
  • This will download the image klutchell/rar
  • Execute it
  • In the Dockerfile you can see the "entrypoint" is already the "rar" executable
  • This means, upon execution of "docker run" it starts the rar process.
  • All you must do is work with it like you work with "rar" itself

How does RAR work?

It needs flags as commands, for example: - a command will add to an archive. - If we mount the right directory, we can simply compress files from the command line:

docker run --rm -v ${PWD}:/files klutchell/rar a /files/myrar.rar /files/myfile.txt
  • It creates a new compressed rar file called "myrar.rar" inside the hosts working directory
  • It's fully compliant to rar files

Understanding the "Working Directory"

As you see above, we need to give the container the full path (/files/...). By specifying a working directory, you can instruct docker to basically start inside that directory (like cd'ing inside):

docker run --rm -v ${PWD}:/files -w /files klutchell/rar a myrar.rar myfile.txt
  • The "-w /files" flag sets the working directory to /files.
  • It's like "cd /files" inside the container and we can skip the full path to the files we want to compress