August 12, 2017

Saving Command History in Containers

We cover two ways of persisting data in containers:

  • Re-using a single container
  • Sharing saved data amonst many containers

The Tinker Command

Laravel's tinker command uses Psysh for a PHP REPL.

When we run artisan tinker, command history is saved in ~/.config/psysh/psysh_history.

It does this using the HOME environment variable to find the `.config/psysh` directory: $HOME/.config/psysh

We can save history in one of two ways with Docker.

Re-use a container

docker run -it \
    -e "HOME=/home" \
    -v ~/.dckrconfig:/home/.config \
    -v $(pwd):/opt \
    -w /opt \
    php:7.0-cli \
    php artisan tinker

Once tinker is started, we can run some commands, then stop the container. Since we didn't use the --rm flag, the stopped container will still exist.

$ docker ps -a

CONTAINER ID    IMAGE        COMMAND                  STATUS        NAMES
6e9c39b313ed    php:7.0-cli  "php artisan tinker"     Exited (0)    high_visvesvaraya

$ docker start -i 6e9c39b313ed

The container was not destroyed when it was stopped! Any change made inside the container is persisted. We'll still have the tinker command history available if we restart the container!

Volumes to Save History

Alternatively, we can still destroy container when we're done with them, but save history locally via a volume mount.

The following sets the $HOME environment variable that Psysh uses to find/create a $HOME/.config/psysh/psysh_history file. On my Macintosh (host system), I create a directory for the container to use to write to the Psysh history to, and then setup the container in a way that Psysh can find/write to that shared volume.

# Create local directory
mkdir ~/.dckrconfig

# Head to my-app
cd ~/Sites/docker/my-app

# Run a container
docker run --rm -it \
    -e "HOME=/home" \
    -v ~/.psyhistory:/home/.config \
    -v $(pwd):/opt \
    -w /opt \
    php:7.0-cli \
    php artisan tinker

This container is destroyed when it is stopped, but since we persisted the Psysh history on a local volume, we can re-use it on future containers by sharing the same directory. We can re-use the exact same command to create a new container anytime - that container will have the previous history as it can read the psysh_history file saved.

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