What is the Lifecycle of Docker container?

Docker containers' lifecycle primarily includes the following stages:

1. Create: During this stage, the docker create command is used to instantiate a new container from a specified image without starting it. This command allows specifying configuration options such as network settings and volume mounts to configure the container for startup.

2. Start: The docker start command is used to initiate a previously created container. During this phase, the application within the container begins running. For example, if the container uses a web service image like Apache or Nginx, the associated services start at this point.

3. Running: After the container is started, it enters the running state. In this phase, the application or service inside the container is active. You can view the container's output using the docker logs command or interact with the container internally via docker exec.

4. Stop: When the container is no longer needed, the docker stop command can be used to halt the running container. This command sends a SIGTERM signal to the container, prompting the application to shut down gracefully.

5. Restart: If necessary, the docker restart command can be used to restart the container. This is particularly useful for quickly restarting services after application updates or configuration changes.

6. Destroy: When the container is no longer needed, the docker rm command can be used to remove it. If the container is still running, it must be stopped first, or the docker rm -f command can be used to forcefully remove a running container.

Example: Suppose we have a web server container based on Nginx. First, we create a container instance:

bash
docker create --name my-nginx nginx

Then, we start this container:

bash
docker start my-nginx

During operation, we might need to view logs or enter the container:

bash
docker logs my-nginx
docker exec -it my-nginx /bin/bash

Finally, when the container is no longer needed, we stop and remove it:

bash
docker stop my-nginx
docker rm my-nginx

This completes the full lifecycle of a Docker container, from creation to destruction.