devops-exercises

Run, Forest, Run!

Objective

Learn what restart policies do and how to use them

Requirements

Make sure Docker is installed on your system and the service is started

# Fedora/RHEL/CentOS
rpm -qa | grep docker
systemctl status docker

Instructions

1. Run a container with the following properties:
   • image: alpine
   • name: forest
   • restart policy: always
   • command to execute: sleep 15

docker run --restart always --name forest alpine sleep 15

1. Run docker container ls - Is the container running? What about after 15 seconds, is it still running? why?

It runs even after it completes to run sleep 15 because the restart policy is “always”. This means that Docker will keep restarting the same container even after it exists.

1. How then can we stop the container from running?

The restart policy doesn’t apply when the container is stopped with the command docker container stop

1. Remove the container you’ve created

docker container stop forest
docker container rm forest

1. Run the same container again but this time with sleep 600 and verify it runs

docker run --restart always --name forest alpine sleep 600
docker container ls

1. Restart the Docker service. Is the container still running? why?

sudo systemctl restart docker

Yes, it’s still running due to the restart policy always which means Docker will always bring up the container after it exists or stopped (not with the stop command).

1. Update the policy to unless-stopped

docker update --restart unless-stopped forest

1. Stop the container

docker container stop forest

1. Restart the Docker service. Is the container running? why?

sudo systemctl restart docker

No, the container is not running. This is because we changed the policy to unless-stopped which will run the container unless it was in stopped status. Since before the restart we stopped the container, Docker didn’t continue running it after the restart.

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