Tag Archives: docker

Backup and restore docker container configurations

I came across a need to start afresh with my docker setup. I didn’t want to re-create all the port and volume mappings for my various containers. Fortunately I found a way around this by using docker-autocompose to create .yml files with all my settings and docker-compose to restore them to my new docker host.

Backup

Docker-autocompose source: https://github.com/Red5d/docker-autocompose

git clone https://github.com/Red5d/docker-autocompose.git
cd docker-autocompose
docker build -t red5d/docker-autocompose .

With docker-autocompose created you can then use it to create .yml files for each of your running containers by utilizing a simple BASH for loop:

for image in $(docker ps --format '{{.Names}}'); do docker run -v /var/run/docker.sock:/var/run/docker.sock red5d/docker-autocompose $image > $image.yml; done

Simple.

Restore

To restore, install and use docker-compose:

sudo curl -L https://github.com/docker/compose/releases/download/1.21.2/docker-compose-$(uname -s)-$(uname -m) -o /usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose

Next we use another simple for loop to go through each .yml file and import them into Docker. The sed piece escapes any $ characters in the .yml files so they will import properly.

for file in *.yml; do sed 's/\$/\$\$/g' -i $file;
docker-compose -f $file up --force-recreate -d; done

You can safely ignore the warnings about orphans.

That’s it!

Troubleshooting

ERROR: Invalid interpolation format for “environment” option in service “Transmission”: “PS1=$(whoami)@$(hostname):$(pwd)$ “

This is due to .yml files which contain unescaped $ characters.

Escape any $ with another $ using sed

sed 's/\$/\$\$/g' -i <filename>.yml

ERROR: The Compose file ‘./MariaDB.yml’ is invalid because:
MariaDB.user contains an invalid type, it should be a string

My MariaDB docker .yml file had a user: environment variable that was a number, which docker compose interpreted as a number instead of a string. I had to modify that particular .yml file and add quotes around the value that I had for the User environment variable.

Docker – run a cron job for a container from the host

I’ve installed tiny tiny rss as a replacement for Feedly once they started inserting ads that looked like articles. Deceptive advertising. I’m not a fan.

I’ve spun up linuxserver’s version of it in docker and it works pretty well except for updating articles. I couldn’t find a great guide on configuring it for updates specifically within a docker container, so here is mine. My solution was to have a cron job running on the docker host to run the feed update script within the docker container, inspired by this post.

The trick is to use the docker exec command to run a command from the docker host but execute it within the running container.

docker exec -u 1001 -it TinyTinyRSS /usr/bin/php /config/www/tt-rss/update.php --feeds --quiet

The -u command specifies which user ID to run the command as. TinyTinyRSS is the name of my container. I’ve set this to run every 15 minutes with the following crontab syntax:

*/15 * * * * /usr/bin/docker exec -u 1001 -d TinyTinyRSS /usr/bin/php /config/www/tt-rss/update.php --feeds --quiet

edit: Modified the crontab entry to make it work properly per this post.