Proper way for keep process running on a container - linux

Question

I'm not aware if this could be considered as a duplicate since it's a problem for an specific case.
Currently, I have created a docker outside docker image for handling my Jenkins agent which will perform auto restarts without using supervisor as a solution ( lack of python 3.7 support ), and by that, since I'm using openjdk:slim as base image and I don't want to install any additional dependencies I opted to compensate the lack of tools like lsof and ps, or others for checking if the process is running or not, by writing the started process pid on a file which will be used for validating if the process exists or not under the path /proc/pid/status. Currently this works and the main reason of creating this solution for handling the auto start of the agents.
But my question is, Is this the best or more appropriated approach?
Please find the following code with the implementation:
#!/bin/bash
set -e
agent_runner() {
while :
do
if [ ! -f "/proc/$(cat /tmp/agent.pid)/status" ]
then
curl $JNLP_AGENT_DOWNLOAD_URL -o agent.jar
java \
-Dorg.jenkinsci.plugins.durabletask.BourneShellScript.HEARTBEAT_CHECK_INTERVAL=300 \
-Dhttps.protocols=TLSv1.2 \
-jar agent.jar \
-jnlpUrl $JNLP_AGENT_URL \
-secret $JENKINS_SECRET \
-workDir "$JENKINS_WORKDIR" &
echo $! > /tmp/agent.pid
else
:
fi
sleep 10
done
}
while :
do
if [ cat < /dev/tcp/"$TARGET" ]; then
echo "Starting Agent"
agent_runner
else
echo "Jenkins master is offline, waiting...."
fi
sleep 10
done
Link for the repository: https://github.com/thcp/jenkins-agent-dod

Answer 1

If the main process in the container dies, you should let the container die with it.
Docker and the various layers above it have functionality to restart whole containers. There is a docker run --restart option for the basic Docker CLI, and equivalent Docker Compose option, and restarting dying containers after some backoff is the default behavior for Kubernetes pods.
So, if you just let a container die on its own, you’ll have out-of-the-box support for the container engine to restart itself, without adding any special support into your image; just set the CMD to the thing you actually need the container to do and go. This approach also has the benefit that if you detect your environment has become unstable (“I depend on a database and it’s unreachable”) the process can choose to abort itself and let it be restarted later when hopefully the environment has improved.