README.md

Running cypress/included image as non-root mapped

If we don't want to run cypress/included image as built-in default root user, we can use node user that already exists in the image thanks to the very base node image. But, if that user creates any files on the host machine, then these files are owned by the node user id and group that might NOT even be present on the host machine.

We want to run inside the Docker container as the non-root user from the host machine with the same id and group id. Then when the container exits, any new files are "magically" owned by the host machine's user.

Read Running Docker Containers as Current Host User for general approach. In general we are going to:

• find out the user id and group on the host machine
• build a custom Docker image from cypress/included image
• in the custom image we will create a new user with matching user and group id (if possible)
• run tests as the new user which matches the user on the host machine

Any files generated by the new user during Cypress run will be owned the non-root user on the host machine.

Steps

See Dockerfile that you can build using build.sh. You can pass your own user and group ids via arguments, I will use default value 501 for the user id, which is my id on current Mac.

$ ./build.sh
...
id
uid=501(appuser) gid=999(appuser) groups=999(appuser)

So the appuser inside the container has same user ID as my host user.

Let's demonstrate the permissions are set correctly. I will start the shell inside the container.

$ docker run -it -v $PWD/src:/test -w /test -u appuser --entrypoint /bin/sh cypress/example
$ ls -la
total 12
drwxr-xr-x 5 appuser appuser  160 Dec 18 20:26 .
drwxr-xr-x 1 root    root    4096 Dec 18 20:33 ..
drwxr-xr-x 4 appuser appuser  128 Dec 18 20:09 cypress
-rw-r--r-- 1 appuser appuser   78 Dec 18 20:09 cypress.json
-rw-r--r-- 1 appuser appuser   58 Dec 18 20:09 index.html

Great, all files inside the container are mapped from the host machine - and yet they have the right user and group, since the numbers match the host user id. Here is for example the same folder on the host machine:

$ ls -la src
total 16
drwxr-xr-x  5 gleb  staff  160 Dec 18 15:26 .
drwxr-xr-x  7 gleb  staff  224 Dec 18 15:09 ..
drwxr-xr-x  4 gleb  staff  128 Dec 18 15:09 cypress
-rw-r--r--  1 gleb  staff   78 Dec 18 15:09 cypress.json
-rw-r--r--  1 gleb  staff   58 Dec 18 15:09 index.html

We can run Cypress using test.sh to confirm the tests pass.

$ ./test.sh
Running tests against cypress/example
Running as a non-root user 'appuser' mapped to host user
++ docker run -it -v ...included-as-non-root-mapped/src:/test -w /test -u appuser cypress/example

The generated video of the test run is owned by the user on the host machine

$ ls -la src/cypress/videos/
total 64
drwxr-xr-x  3 gleb  staff     96 Dec 18 15:35 .
drwxr-xr-x  4 gleb  staff    128 Dec 18 15:09 ..
-rw-r--r--  1 gleb  staff  32299 Dec 18 15:35 spec.js.mp4