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Container Lifecycle

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Understanding the lifecycle of a Docker container is crucial for effectively managing and utilizing containers in your development and production environments. This section will cover the different states a container can be in, the commands to manage these states, and practical examples to solidify your understanding.

Key Concepts

  1. Container States:

    • Created: The container has been created but not started.
    • Running: The container is currently executing.
    • Paused: The container is temporarily stopped.
    • Stopped: The container has been stopped.
    • Exited: The container has finished executing and has stopped.
    • Removed: The container has been deleted.

  2. Lifecycle Commands:

    • docker create: Create a new container.
    • docker start: Start a stopped container.
    • docker stop: Stop a running container.
    • docker pause: Pause a running container.
    • docker unpause: Unpause a paused container.
    • docker restart: Restart a running or stopped container.
    • docker rm: Remove a container.

Practical Examples

Creating a Container

docker create --name my_container ubuntu
  • Explanation: This command creates a new container named my_container using the ubuntu image. The container is in the Created state.

Starting a Container

docker start my_container
  • Explanation: This command starts the my_container container, changing its state to Running.

Stopping a Container

docker stop my_container
  • Explanation: This command stops the my_container container, changing its state to Stopped.

Pausing a Container

docker pause my_container
  • Explanation: This command pauses the my_container container, changing its state to Paused.

Unpausing a Container

docker unpause my_container
  • Explanation: This command unpauses the my_container container, changing its state back to Running.

Restarting a Container

docker restart my_container
  • Explanation: This command restarts the my_container container, stopping it if it is running and then starting it again.

Removing a Container

docker rm my_container
  • Explanation: This command removes the my_container container, changing its state to Removed.

Practical Exercise

Exercise: Managing Container Lifecycle

  1. Create a new container named test_container using the alpine image.
  2. Start the test_container.
  3. Pause the test_container.
  4. Unpause the test_container.
  5. Stop the test_container.
  6. Restart the test_container.
  7. Remove the test_container.

Solution

# Step 1: Create a new container
docker create --name test_container alpine

# Step 2: Start the container
docker start test_container

# Step 3: Pause the container
docker pause test_container

# Step 4: Unpause the container
docker unpause test_container

# Step 5: Stop the container
docker stop test_container

# Step 6: Restart the container
docker restart test_container

# Step 7: Remove the container
docker rm test_container

Common Mistakes and Tips

  • Forgetting to start a container: After creating a container, you must start it using docker start.
  • Not stopping a container before removing it: Ensure the container is stopped before attempting to remove it.
  • Using the wrong container name: Double-check the container name when using lifecycle commands to avoid errors.

Conclusion

In this section, you learned about the different states a Docker container can be in and the commands to manage these states. By practicing the provided examples and exercises, you should now be comfortable with managing the lifecycle of Docker containers. This knowledge is fundamental as you progress to more advanced Docker topics.

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