Hello. In this tutorial, we will talk about Docker and container restart in docker.
1. What is Docker?
In the present world, Docker is an important term –
- Often used in CI/CD platform that packages and runs the application with its dependencies inside a container
- Is a standard for Linux Containers
- A Container is a runtime that runs under any Linux kernel and provides a private machine-like space under Linux
1.1 What is Docker used for?
It is used for –
- For environment replication, while the code runs locally on the machine
- For numerous deployment phases i.e. Dev/Test/QA
- For version control and distributing the application’s OS within a team
1.2 Basic Docker terminology?
- Image: Representation of Docker container i.e. a JAR or WAR file in Java
- Container: Runtime of Docker i.e. a deployed and running Docker image. For example, an executable Spring Boot jar
- Engine: The code that manages, creates, and runs the Docker containers
- Hub: A public developer’s registry to distribute their code
- Repository: A collection of Docker-related images i.e. different versions of the same application
1.3 Setting up Docker
If someone needs to go through the Docker installation, please watch this video.
2. Restart the Docker container
Docker has a straightforward syntax for restarting one or more containers. A docker container is restarted because of the following reasons –
- The main process gets terminated after successful tasks execution
- The main process gets terminated abruptly when a container is stopped forcefully
- When the docker container is stopped
- When the docker is restarted
- When the docker container consumes too much memory
The syntax is represented by the below syntax and it supports OPTIONS like --all, --time, and --quiet.
Command syntax
docker restart OPTIONS CONTAINER_NAME
If a case multiple containers are to be restarted one can use the below command.
Restart multiple containers at once
docker restart $(docker ps -a -q)
2.1 Docker restart policy
Docker also let the user set the restart policy upon exit or failure. The restart policy is represented by –
Command syntax
docker run --restart=RESTART_POLICY_NAME CONTAINER_NAME
The command supports the following restart policies.
| Restart policy name | Result |
no | Do not automatically restart the container when the container exits. It is a default behavior |
on-failure[:max-retries] | Restart only if the container exists with a non-zero exit status |
always | Always restart the container regardless of the exit status |
unless-stopped | Always restart the container regardless of the exit status, including on daemon startup, except if the container was put into a stopped state before the docker daemon was stopped |
3. Demo
Let us dive into a practical demo.
3.1 Restarting a stopped container
Let us restart a stopped httpd container and for that, we’ll use the restart command. In the below command, upbeat_lichterman is the container name.
Command 1
docker restart upbeat_lichterman
If everything goes well the container will be restarted.
3.2 Running a container via policy
Let us run a Redis container with a restart policy of always. This will ensure that the container will be automatically restarted upon exit of failure. Users can use docker ps to check if the restart policy is active or not.
Command 2
docker run --name demo-redis -d --restart=always -p 6379:6379 redis
That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share! Happy learning and do not forget to share!
4. Summary
In this tutorial, we learned about Docker and the restart action of a docker container. You can also download the commands used in this tutorial from the Downloads section.
5. Download the Project
This was a tutorial on the restart action of a docker container.
You can download the full source code of this example here: Restart Docker Container
