Hacktoberfest is upon us! This month I’m hacking on small projects each week and sharing them.

We Continue…

Last week, my son and I recently ventured out to start a Minecraft server as part of Hacktober fest. This week we are planning on automating that server a bit more. A few days after playing on the server, we restarted it to test things out. Ultimately, this did work and the server came back up, but the world data was not saved and we had no backups. Thinking out loud, we brainstormed both why this happened and how we could prevent it in the future. We certainly don’t want to build an awesome structure then lose it when the server restarts! Backups were definitely in the back of my mind, as were persisted version-controlled configurations for the server (currently after restarting, all the settings are reset to the defaults). So we set about trying to find a backup solution.

Sounds Simple

We definitely wanted to automate backups. After reading a lot about how Minecraft saves files, we knew the backup was rather simple:

save-off
save-all
tar czf /opt/backups/$(date +%Y-%m-%d)-mc-${CLIENT}.tar.gz /opt/minecraft/
save-on

Sounds simple enough right? Wrong! These commands are all sent the Minecraft server from an RCON client. A quick search finds a lot of options! So far, so good. Since the Docker image we were using for Minecraft included an RCON client… but it didn’t really do backups. At least, not the way I wanted to. So, we decided to create our own Dockerfile for our Minecraft server!

DIY

After much searching we found a very simple and very compact Minecraft RCON client written in Go! Why not? There are no dependencies on a VM or additional libraries. This should be dead simple to include in our Minecraft Server Dockerfile. Of course, as are many things that seem simple, it was not as simple as we originally thought. In our build automation, we included a stage called “setup” running on the latest Golang image. Then we simply run a script to go get and go install the Go application. We used the artifacts instruction to share this compiled binary to the next stage which copies it to our Minecraft Server Dockerfile. Now we have an RCON client!

We wanted backups to happen automatically, so we added a backup script. This script runs using Cron to periodically backup the Minecraft Server files and copy them to a backups directory. The idea here is to mount a volume to this directory so it can be used in another container (the one that will ultimately move it to Dropbox). Once we got that set up we ran the pipeline and…

It failed… The custom GitLab Runner image I had hobbled together a few months ago wasn’t working as expected. It wouldn’t pull the Golang image, so we couldn’t get the Go binary. I had been experiencing many problems with this image and was sure I probably made it wrong. I at least didn’t make it in a repeatable fashion. I definitely didn’t have it running in a container… So, we decided to shift our focus to making a new GitLab Runner image in the way I had intended — in a repeatable fashion preferably containerized. So we spun up a new repository to build this container…

With automated deploys in mind, this should be relatively easy. We created a new .gitlab-ci.yml file and had the job run in a docker:latest container (ie: Docker-in-Docker). All this job is going to do s pull the latest GitLab Runner image, configure it, then run it. Let’s see how this works:

image: docker:latest
variables:
  DOCKER_DRIVER: "overlay2"
script:
  - "docker pull gitlab/gitlab-runner:latest"
  - "docker run -d --name gitlab-runner \
    --restart always \
    -v ${GITLAB_VOLUME}:/etc/gitlab-runner \
    -v /var/run/docker.sock:/var/run/docker.sock \
    gitlab/gitlab-runner:latest"
tags:
  - docker

We push and.. wait a second.. before we push let’s walk through this… We want GitLab to automatically deploy a GitLab Runner… This isn’t repeatable. If I were to tear down the current GitLab Runner, this would never run! This can’t be the solution.. let’s take a step back…

We know we want this automated. The first time we run it, there won’t be any automation at all! We can’t use the YAML file! We must use a Shell Script (or some other script)! Let’s take a look at what we need to do

#!/bin/bash
# If docker is not installed, go get it
command -v docker >/dev/null 2>&1 || {
  curl -sSL https://get.docker.com/ | sh
}
# Set defaults
VERSION="latest"
function usage() {
  echo "This script automatically installs Docker and runs a GitLab Runner container."
  echo " ./run.sh -t [options]"
  echo " -t, --token : (Required) The GitLab Token of the container"
  echo " -n, --name : (Required) The name of the container"
  echo " --alpine : (Optional) Use the Alpine version of the gitlab-runner container"
  exit 1
}
#Parse command line options
while [[ $# -gt 0 ]]; do
  case $1 in
    -n | --name)
      NAME="$2"
      shift # past argument
      shift # past value
    ;;
    --alpine)
      VERSION="alpine"
      shift # past argument
    ;;
    -t | --token)
      TOKEN="$2"
      shift # past argument
      shift # past value
    ;;
    *)
      usage
    ;;
  esac
done
if [ -z ${TOKEN} ]; then
      echo "Token is required!"
      usage
fi
if [ -z ${NAME} ]; then
      echo "Name is required!"
      usage
fi
# Create a volume that will persist
docker stop -t 0 ${NAME} || true
docker rm ${NAME} || true
docker run -d --name ${NAME} \
  --restart always \
  -v /var/run/docker.sock:/var/run/docker.sock \
  gitlab/gitlab-runner:${VERSION}
#Register with GitLab
docker exec ${NAME} gitlab-runner register \
  --non-interactive \
  --executor "docker" \
  --docker-image alpine:latest \
  --url "https://gitlab.com/" \
  --registration-token "${TOKEN}" \
  --name "${NAME}" \
  --docker-privileged \
  --tag-list "docker" \
  --run-untagged \
  --locked="false"

There. Now we have a script that can take a container name and your GitLab Runner token then spawn a new docker privileged container. I decided to not mount a config volume as it would continuously add new runner configs when the service restarted. There is a bit of cleanup in GitLab under the CI/CD runners section when a runner is restarted, but that seems to not be a big deal at the moment. Now that we have a new repeatable GitLab Runner up, we can try to get that Minecraft Dockerfile working next time!

Leave a Reply

Your email address will not be published. Required fields are marked *