Keeping your Pi-Hole container fresh with Cron

In our previous entry, we unleashed the awesome that is Pi-Hole inside a Docker container to make all the devices in our network ad-free when browsing the internet. Now while that is a good start, you want to keep your container running the latest and greatest version of Pi-Hole right? Now while the containerised version disables Pi-Holes built in upgrade mechanisms, you still can upgrade it in a way that containers are designed to…by phoenixing them!

Refresh the container script

First off, lets open up nano (or your favourite text editor) and create a script file:

nano refreshpihole.sh

Next, punch in the following code:

#!/bin/bash

docker pull diginc/pi-hole-multiarch:debian_armhf
docker rm -f pihole
/path/to/pihole/launch/script.sh

If you have checked out any of my other Docker based posts, the above should be self explanatory.

docker pull diginc/pi-hole-multiarch:debian_armhf

This downloads the latest version of the container image. Remember to confirm which image:tag you require for your particular device.

docker rm -f pihole

The above then goes and trashes the currently running Pi-Hole container.

/path/to/pihole/launch/script.sh

Last but not least, we execute the previously created Pi-Hole script to launch it once more, albeit with a fresh and updated image.

Once you have saved and exited out of the script, don’t forget to make it executable with CHMOD.

Schedule the script with Cron

Cron, named after the Greek word for time, chronos, is a scheduling system across Linux distributions. Cron has various ways to schedule commands and scripts. One way is with the crontab -e command which will open the per user Cron schedule with a custom version of the text editor VIM. Alternatively, there are predefined folders under /etc/:

Simply copy your script file to refresh the Pi-Hole installation to the folder of your choice and it will be executed by Cron on that schedule:

sudo cp /path/to/script/refreshpihole.sh /etc/cron.monthly

With the above, Cron will execute our copied script (and any others in that folder) on a monthly basis.

Summary

The above gives us a small but important example in how Docker and container systems broadly  are advantageous over running apps and services on a traditional virtual machine with (hopefully) a patching regime in place. Here we have a important component of our infrastructure that is being kept up to date, has a small footprint across our file-system and operating system, while keeping configuration and logs persistent with minimal downtime.

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