2.8 Lab - Labeling Containers

Introduction

This hands-on lab is designed to provide practical experience with labeling Docker containers and images. Labels are a powerful feature in Docker that allows you to attach metadata to your Docker objects, making it easier to manage, organize, and query your containers and images. Through this lab, you'll learn how to apply labels to Docker images and containers and how to utilize these labels for management and querying purposes.

Objectives

• Learn how to add labels to Docker images during the build process.
• Understand how to label Docker containers at runtime.
• Practice querying Docker objects by their labels.

Lab Steps

Step 1: Preparing Your Environment

• Ensure Docker is installed on your Linux system. Confirm the installation by running docker --version in your terminal.

Step 2: Creating a Dockerfile with Labels

• Create a new directory for your Docker project:

mkdir labeled-docker-app
cd labeled-docker-app

• Use Nano to create a Dockerfile: nano Dockerfile.
• Add the following content to the Dockerfile, including labels:

  # Base image
  FROM nginx:latest
  # Adding labels
  LABEL org.example.version="0.1" \
        org.example.description="This is a labeled custom Nginx image."
  

• Save and exit Nano (CTRL+O, Enter, CTRL+X).

Step 3: Building Your Labeled Image

• Build the Docker image with the labels specified in the Dockerfile:

  docker build -t labeled-nginx .
  

• Verify the labels are embedded in the image: docker inspect labeled-nginx.

Step 4: Running a Container with Additional Labels

• Run a container from your labeled image and add extra labels at runtime:

  docker run -d --name my-labeled-nginx --label "org.example.environment=development" labeled-nginx
  

• Verify the container is running and has the runtime label:

docker inspect my-labeled-nginx

You should see something like this in the output:

   "Labels": {
                "maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>",
                "org.example.description": "This is a labeled custom Nginx image.",
                "org.example.environment": "development",
                "org.example.version": "0.1"
            },

Step 5: Querying Containers by Labels

• Use the Docker CLI to filter and list containers by their labels:

  docker ps --filter "label=org.example.environment=development"
  

• This command should list your my-labeled-nginx container.

CONTAINER ID   IMAGE           COMMAND                  CREATED         STATUS              PORTS     NAMES
be6ba8ac786b   labeled-nginx   "/docker-entrypoint.…"   2 minutes ago   Up About a minute   80/tcp    my-labeled-nginx

Summary

In this lab, you've gained hands-on experience with Docker's labeling feature, learning how to apply labels to both images and containers. You've created a Dockerfile with embedded labels, built a labeled image, and run a container with additional labels applied at runtime. Finally, you practiced querying and filtering Docker objects based on their labels, demonstrating the power and flexibility of labels for managing Dockerized environments. Understanding and utilizing labeling effectively is key to organizing and automating tasks in complex Docker deployments, enhancing your Docker management capabilities.