dev-ops-challenges

Deploy Nginx Container on Application Server

Technical Overview

Modern cloud-native and DevOps workflows rely heavily on containerization to package applications along with all their dependencies, configurations, and libraries. This ensures consistency across development, staging, and production environments. Docker is the industry-standard containerization platform used to build, run, and manage containerized software.

Why Containerize Nginx?

Running Nginx in a container offers several key benefits:

Isolation: The web server runs in a sandbox, preventing conflicts with other packages or configurations on the host system.
Speed & Efficiency: Using a lightweight Alpine-based container image minimizes disk space and memory footprint while accelerating startup times.
Portability: The identical configuration runs the exact same way on a local developer laptop, a staging virtual machine, or a Kubernetes cluster.

Docker Port Exposure and Binding

By default, Docker containers are isolated from the host machine’s external network. They are assigned an internal IP address accessible only from the host or other containers on the same Docker network.

To allow external clients to access Nginx (which listens on port 80 by default inside the container), we must map the container’s port to a port on the host machine. This is done using the -p (or --publish) flag.

sequenceDiagram
    actor Client as External Client (e.g. Browser/curl)
    participant Host as Host Server (stapp03)
    participant Docker as Docker Daemon (iptables/proxy)
    participant Container as Nginx Container (nginx_3)

    Client->>Host: Request http://stapp03:8080
    Host->>Docker: Route incoming port 8080 traffic
    Docker->>Container: Forward traffic to container port 80
    Container-->>Docker: Send HTTP Response (Welcome to Nginx)
    Docker-->>Host: Pass response
    Host-->>Client: Respond to client

When a port is published, Docker sets up iptables rules or starts a docker-proxy process on the host to forward incoming connections to the container’s internal network interface.

Infrastructure & Configuration Requirements

Target Host: Nautilus App Server 3 (stapp03)
SSH User: banner
Container Name: nginx_3
Container Image: nginx:alpine
Port Mapping: Expose container port 80 to host port 8080 (or 80)

Step-by-Step Implementation

Step 1: Connect to the Application Server

Establish an SSH connection from the Jump Host to App Server 3:

ssh banner@stapp03

Provide the server password when prompted.

Step 2: Verify Docker Daemon Status

Verify if Docker is installed and running on the target application server:

# Check service status
sudo systemctl status docker

If Docker is stopped, start it and optionally enable it to start on boot:

# Start Docker service
sudo systemctl start docker

# Enable Docker on boot
sudo systemctl enable docker

Step 3: Run the Nginx Container

To deploy the Nginx container as specified in the challenge, use the standard docker run command.

Standard Run Command (Minimal):

docker run -d --name nginx_3 nginx:alpine

Run Command with Port Exposure:

To expose the web server to the host network so external clients can access it on port 8080:

docker run -d --name nginx_3 -p 8080:80 nginx:alpine

Understanding the `docker run` Options

Flag	Option	Description
`-d`	Detached Mode	Runs the container in the background and prints the container ID. The terminal remains free for further commands.
`--name nginx_3`	Container Name	Assigns a custom name (`nginx_3`) to the container. If omitted, Docker assigns a random string name.
`-p 8080:80`	Port Publishing	Maps `<host_port>:<container_port>`. Any traffic coming to port `8080` on the host will be forwarded to port `80` inside the container.
`nginx:alpine`	Image	Specifies the image to run. The `:alpine` tag indicates that the container uses a lightweight Alpine Linux distribution as its base.

Step 4: Verify Container Execution

Ensure that the container was launched successfully and is in the Up state:

docker ps -a

Expected Output:

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS         PORTS                  NAMES
c2b8c9d0e1f2   nginx:alpine   "/docker-entrypoint.…"   5 seconds ago   Up 5 seconds   0.0.0.0:8080->80/tcp   nginx_3

Post-Deployment Verification

1. Test Web Server Accessibility

Use curl on the host machine to make an HTTP request to the exposed port:

curl http://localhost:8080

Expected Output (Nginx Welcome Page HTML):

<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...

2. Inspect Container Logs

If the container fails to start, or to view access requests, inspect the container logs:

docker logs nginx_3

3. Retrieve Detailed Container Metadata

To inspect environment variables, IP address configuration, and port bindings:

docker inspect nginx_3

Log out of the Application Server:

exit