Container Networking and Security Lab (Codespaces Edition)

Overview

In this lab, you will:

• Run Docker containers
• Explore container networking
• Create and use a custom bridged network
• Inspect container IP addresses
• Test connectivity between containers
• Deploy a web server (nginx)
• Validate your work using an automated check script

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Step 0: Open in Codespaces

1. Fork this repository to your GitHub account.
2. Navigate to your forked repository and select: Code → Codespaces → Create codespace
3. Wait for the environment to start.

Note: Docker is pre-installed in this Codespace. You do not need to install Docker manually. The environment is ready for container networking tasks.

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Step 1: Verify Docker

What these commands do:

• docker --version shows the installed Docker version to confirm Docker is available.
• docker ps lists running containers (should be empty at first).

docker --version
docker ps

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Step 2: Pull Ubuntu Image

What these commands do:

• docker pull ubuntu:focal downloads the Ubuntu image (version focal) from Docker Hub so you can use it for containers.
• docker images lists all images available locally, including the one you just pulled.

docker pull ubuntu:focal
docker images

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Step 3: Create a Custom Bridge Network

What these commands do:

• docker network create --driver bridge csf-net creates a new custom bridge network named csf-net for your containers to use. This network isolates your containers from others and lets you control their communication.
• docker network ls lists all Docker networks, so you can confirm your new network was created.

docker network create --driver bridge csf-net 
docker network ls

Why?

A user-defined bridge network (csf-net) allows containers to communicate securely and predictably. Unlike the default bridge, it provides better network isolation and lets you control which containers can talk to each other. This is important for container security, as it limits exposure and enables network segmentation—key principles in secure container deployments.

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Step 4: Run the First Container (on the custom network)

What this command does:

• docker run -it -d --name csf-ubuntu1 --network csf-net ubuntu:focal starts a new Ubuntu container named csf-ubuntu1 in the background, attached to the csf-net network. The -it allows interactive mode, and -d runs it detached (in the background).

docker run -it -d --name csf-ubuntu1 --network csf-net ubuntu:focal

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Step 5: Run the Second Container (on the custom network)

What this command does:

• docker run -it -d --name csf-ubuntu2 --network csf-net ubuntu:focal starts a second Ubuntu container named csf-ubuntu2, also attached to the csf-net network, so it can communicate with the first container.

docker run -it -d --name csf-ubuntu2 --network csf-net ubuntu:focal

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Step 6: Get Container IP Address

What this command does:

• docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' csf-ubuntu1 shows the internal IP address of the csf-ubuntu1 container on the custom network. You will use this IP to test connectivity.

docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' csf-ubuntu1

Save this IP address for later use.

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Step 7: Access the Second Container’s Shell

What this command does:

• docker exec -it csf-ubuntu2 /bin/bash opens a shell inside the csf-ubuntu2 container so you can run commands inside it.

docker exec -it csf-ubuntu2 /bin/bash

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Step 8: Update Packages

What this command does:

• apt-get update refreshes the list of available software packages inside the container, so you can install new tools.

apt-get update

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Step 9: Install Ping

What this command does:

• apt-get install iputils-ping -y installs the ping tool inside the container, which is needed to test network connectivity. The -y flag auto-confirms the install.

apt-get install iputils-ping -y

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Step 10: Test Connectivity

What this command does:

• ping <IP_ADDRESS> sends network test packets to the IP address of the first container. If you see replies, the containers can communicate over the custom network.

Replace <IP_ADDRESS> with the value from Step 5. You should see successful replies.

Exit the container shell with:

exit

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Step 11: Run the Nginx Web Server

What this command does:

• docker run -d -p 8080:80 --name csf-nginx nginx:latest starts an Nginx web server container named csf-nginx, mapping port 8080 on your Codespace to port 80 in the container. The -d flag runs it in the background.

docker run -d -p 8080:80 --name csf-nginx nginx:latest

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Step 12: Access the Web Server

What to do:

• Go to the Ports tab in Codespaces.
• Open port 8080.
• You should see: "Welcome to nginx!"

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Step 13: Check Your Work and Get Your Marksheet

Run the check script:

bash check.sh

This will generate a marksheet.md file with your GitHub username and a summary of your lab checks. Your instructor will use this for grading.