How to stop and start a running container?

Stopping and Starting a Running Docker Container

As a Docker expert and mentor, I'm happy to help you with your question on how to stop and start a running Docker container.

Stopping a Running Container

To stop a running Docker container, you can use the docker stop command. This command sends a SIGTERM signal to the main process running inside the container, giving it a chance to gracefully shut down.

Here's the basic syntax:

docker stop [CONTAINER_ID or CONTAINER_NAME]

You can obtain the CONTAINER_ID or CONTAINER_NAME by running the docker ps command, which lists all the running containers.

For example, to stop a container with the name "my-app":

docker stop my-app

If the container doesn't stop within the default timeout (10 seconds), you can use the --time or -t flag to specify a custom timeout value:

docker stop -t 30 my-app

This will give the container 30 seconds to stop before Docker sends a SIGKILL signal to forcefully terminate the container.

Starting a Stopped Container

To start a stopped Docker container, you can use the docker start command. This command will start the container using the same configuration and settings as when it was last stopped.

Here's the basic syntax:

docker start [CONTAINER_ID or CONTAINER_NAME]

For example, to start a container with the name "my-app":

docker start my-app

If you need to attach to the container's standard input, output, and error streams after starting it, you can use the docker attach command:

docker attach my-app

This will connect your terminal to the container's console, allowing you to interact with the running application.

Visualizing the Docker Container Lifecycle

Here's a Mermaid diagram that illustrates the lifecycle of a Docker container:

This diagram shows that you can create a new container, start it, and it will be in a running state. From the running state, you can stop the container, which will put it in a stopped state. You can then start the stopped container again to resume its execution.

Real-World Example

Imagine you're running a web server container that hosts your company's website. During a software update, you need to stop the container, apply the changes, and then start the container again to put the new version of the website online.

1. You run docker stop my-website to gracefully stop the running container.
2. You make the necessary changes to the application code and build a new Docker image.
3. You run docker start my-website to start the container with the updated code.
4. Your users can now access the new version of the website.

By understanding how to stop and start Docker containers, you can effectively manage the lifecycle of your containerized applications and ensure seamless updates and deployments.