Docker for DevOps Engineers

What is Docker?

• Open platform to package, deploy, and manage applications in containers.

• Allows bundling an app with all its dependencies into a standardized unit (container).

Containers - Standardized units that package code, runtime, and dependencies to isolate apps.

Docker Architecture:

Docker Client: The Docker client is the primary user interface to interact with Docker. It allows you to send commands to the Docker daemon - the background service that builds and runs containers.

The client takes commands from the user and communicates them to the daemon. For example:

• docker build - Builds a container image from a Dockerfile

• docker run - Starts a container from an image

• docker pull - Downloads Docker images from a registry

• docker ps - Lists running containers

Docker Host: Docker host provides the runtime environment for building and running Dockerized applications and services in containers. It's where the Docker daemon and containers live.

Docker Registry: A Docker registry serves as a shared storage and distribution system for Docker images within teams and publicly.

Common registry types:

• Public registry - Docker Hub

• Private (enterprise-grade) registry - Docker Trusted Registry

• Third-party registries - AWS ECR and GitLab etc.

Tasks:

Use the docker run command to start a new container and interact with it through the command line. [Hint: docker run hello-world]

docker run -d -p 80:80 --name mynginxapp nginx

• docker run - Runs a new container from the specified image

• -d - Runs the container in detached/background mode

• --name mynginxapp - Names the container "my-nginx"

• nginx - Specifies the image name to use (nginx in this case)

• -p 80:80 - maps container 80 to host 80 explicitly.

Use the docker inspect command to view detailed information about a container or image.

docker inspect mynginxapp

• docker inspect - Gets detailed information about a container or image

• mynginxapp - The name/ID of the container or image to inspect

Use the docker port command to list the port mappings for a container.

docker port my-nginx

• docker port - Lists the exposed ports and mappings for a container

• mynginxapp - The name/ID of the container to list port info for

Use the docker stats command to view resource usage statistics for one or more containers.

docker stats mynginxapp

• docker stats - Provides live resource usage stats for containers

• mynginxapp - The name/ID of the container to get stats for

Use the docker top command to view the processes running inside a container.

docker top mynginxapp

• docker top - Shows running processes in a container

• mynginxapp - The name/ID of the container to get process info for

Use the docker save command to save an image to a tar archive.

docker save -o mynginxapp.tar nginx

• docker save - Saves an image to a .tar archive

• -o mynginxapp.tar - Output to a file called nginx-image.tar

• nginx - The name of the image to save

Use the docker load command to load an image from a tar archive.

docker load -i nginx-image.tar

• docker load - Loads an image from a .tar archive

• -i mynginxapp.tar - Input from the nginx-image.tar file

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