# Networking Deep Dive & Bash Scripting Adventures ## Introduction Hello there! 👋 This past week marked the **third week** of my DevOps journey, and it has been an **exciting and challenging** one. I dived deep into **how DNS works, the TCP/IP model, Bash scripting, and built some projects along the way**. I also faced my fair share of errors (as expected), but overcoming them was a great learning experience. Let's go through each topic in detail! --- ## Exploring the Depths of Networking Last week, I covered the **basics of computer networks**, including the OSI model and network topologies. This week, I explored: ### **1\. How DNS Works** The **Domain Name System (DNS)** is what helps map **human-readable domain names (like** [**google.com**](http://google.com)**)** to **IP addresses** that machines understand. Learning about DNS helped me understand: * The role of **DNS resolvers, root servers, TLD servers, and authoritative name servers**. * How requests flow when a user enters a URL in the browser. ![What is DNS? | How DNS works | Cloudflare](https://cf-assets.www.cloudflare.com/slt3lc6tev37/1NzaAqpEFGjqTZPAS02oNv/bf7b3f305d9c35bde5c5b93a519ba6d5/what_is_a_dns_server_dns_lookup.png align="left") ### **2\. TCP/IP Model** Unlike the **theoretical OSI model**, the **TCP/IP model** is the real-world networking framework we use every day. It consists of the following layers: 1️⃣ **Network Access Layer (Link Layer)** – Deals with physical transmission of data. 2️⃣ **Internet Layer** – Responsible for addressing and routing packets using protocols like IP. 3️⃣ **Transport Layer** – Manages end-to-end communication using protocols like TCP and UDP. 4️⃣ **Application Layer** – Interfaces with user applications like HTTP, SMTP, and FTP. Some resources describe the TCP/IP model as **5 layers**, merging the **Data Link Layer and Physical Layer** into one. Learning about this model made it easier for me to grasp how **data packets travel across networks** and how **routing** works. ![TCP/IP and OSI](https://media.geeksforgeeks.org/wp-content/uploads/20230417045622/OSI-vs-TCP-vs-Hybrid-2.webp align="left") ### **3\. Forward and Reverse Proxy** I also explored **proxy servers** and how they act as intermediaries between clients and the internet: * **Forward Proxy:** Sits between the client and the web, helping in **hiding identity, caching content, and filtering traffic**. * **Reverse Proxy:** Sits between the web server and users, mainly used for **load balancing, security, and caching**. A widely used example of a **Reverse Proxy** is **Nginx**, which I plan to explore in-depth soon. ### **Resources I Used for Networking:** 1. [Networking Basics - YouTube](https://youtu.be/IPvYjXCsTg8?si=dpAkoN1Ga3KAYsIA) 2. [GeeksforGeeks - DNS System](https://www.geeksforgeeks.org/domain-name-system-dns-in-application-layer/) 3. [TCP/IP Explained - YouTube](https://youtu.be/2QGgEk20RXM?si=H8BKfs9BN5zI9p3g) --- ## Getting Started with Bash Scripting After wrapping up Networking, I jumped into **Bash scripting**. The first thing I did was understand **what Bash is and how it differs from other shells**. Then, I got hands-on by writing my first script: ```bash #!/bin/bash # My first Bash script echo "This is my first script as a DevOps Student" echo "Lionel Andres Messi" echo "GOAT" ``` A bit embarrassing, but let's move past that. 😅 I then learned about: * **Variables & Comments** * **If statements & Loops** * **Exit Codes & Functions** * **Command-line arguments & Case statements** To **practice Bash scripting**, I built some small projects like: ✅ **A simple to-do list script** that adds tasks to a file. ✅ **A basic calculator script** for performing arithmetic operations. ### **First Project: Deploying a Django App using Docker & Nginx** Even though I had no prior experience with **Docker and Nginx**, I followed along with a tutorial where the instructor explained each script, ran it, and debugged errors. But while following the tutorial, I encountered an unexpected **error**: ```plaintext error checking context: no permission to read from '/home/vagrant/DevOps-Learning/shell-scripting/script-projects/django-notes-app/data/mysql/db/#ib_16384_0.dblwr' Failed to build and deploy the app. ``` **Solution:** * The error occurred because **Docker didn’t have permission to access the MySQL folder** in the cloned repo. * I used the `chown` command to **give the current user ownership** of the folder. * Then, I modified the **permissions** of the cloned repo. This allowed me to **successfully deploy the app using Docker Compose & Nginx**. However, since I was running my Ubuntu machine in a **VM**, I couldn't access `localhost:8000` directly. Instead, I checked my VM’s IP using `ip addr show` and accessed the port via that IP. --- ### **Second Project: Creating an AWS EC2 Instance using Bash** This project aimed to **automate the process of creating an AWS EC2 instance using Bash scripting**. I was particularly excited about this project as it gave me a **real-world perspective on automation and infrastructure provisioning**. ### **Step 1: Checking AWS CLI Installation** Before proceeding with creating an instance, I needed to ensure that **AWS CLI** was installed. To check this, I wrote the following function: ```bash check_awscli() { if ! command -v aws &> /dev/null; then echo "AWS CLI is not installed. Installing it now..." >&2 return 1 fi } ``` If AWS CLI wasn’t installed, I wanted the script to handle the installation automatically. ### **Step 2: Installing AWS CLI** To automate the installation of AWS CLI on a Linux system, I wrote this function: ```bash install_awscli() { echo "Installing AWS CLI v2 on Linux..." # Download and install AWS CLI v2 curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip" sudo apt-get install -y unzip &> /dev/null unzip awscliv2.zip sudo ./aws/install # Verify installation aws --version || { echo "AWS CLI installation failed. Please install manually." exit 1 } # Clean up rm -rf awscliv2.zip ./aws echo "AWS CLI Installation Completed." } ``` This function **downloads and installs AWS CLI**, verifies the installation, and cleans up unnecessary files. ### **Step 3: Creating the EC2 Instance** Once AWS CLI was installed, I wrote a function to **create an EC2 instance using AWS CLI commands**: ```bash create_ec2_instance() { local ami_id="$1" local instance_type="$2" local key_name="$3" local subnet_id="$4" local security_group_ids="$5" local instance_name="$6" # Run AWS CLI command to create EC2 instance instance_id=$(aws ec2 run-instances \ --image-id "$ami_id" \ --instance-type "$instance_type" \ --key-name "$key_name" \ --subnet-id "$subnet_id" \ --security-group-ids "$security_group_ids" \ --tag-specifications "ResourceType=instance,Tags=[{Key=Name,Value=$instance_name}]" \ --query 'Instances[0].InstanceId' \ --output text ) if [[ -z "$instance_id" ]]; then echo "Failed to create EC2 instance." >&2 exit 1 fi echo "Instance $instance_id created successfully." # Wait for the instance to be in running state wait_for_instance "$instance_id" } ``` This function takes **multiple parameters** such as AMI ID, instance type, key name, subnet ID, security group ID, and instance name. After executing the **AWS CLI command to create an instance**, it waits for the instance to be fully initialized. ### **Step 4: Waiting for Instance to Run** Once the EC2 instance is created, the script waits until the instance reaches the **running** state: ```bash wait_for_instance() { local instance_id="$1" echo "Waiting for instance $instance_id to be in running state..." while true; do state=$(aws ec2 describe-instances --instance-ids "$instance_id" --query 'Reservations[0].Instances[0].State.Name' --output text) if [[ "$state" == "running" ]]; then echo "Instance $instance_id is now running." break fi sleep 10 done } ``` ### **Step 5: Automating AWS Configuration** A key realization was that **AWS CLI requires manual configuration** before usage, which defeats the purpose of full automation. I discovered that AWS credentials are stored in **.aws/config and .aws/credentials**, so I automated this process: ```bash configure_aws() { local aws_access_key="$AWS_ACCESS_KEY_ID" local aws_secret_key="$AWS_SECRET_ACCESS_KEY" local aws_region="$AWS_DEFAULT_REGION" # Ensuring the .aws directory exists mkdir -p ~/.aws cat > ~/.aws/credentials < ~/.aws/config <