Now we’re entering the “network connectivity” section of AWS CloudFormation template — this is what actually connects your private VPC and subnets to the internet 🌐.

Let’s go step by step — we’ll visualize it like you’re wiring up your own mini data center.

🧠 OVERVIEW — What this block does

This part sets up:

1. Internet Gateway → door from your VPC to the internet 🌍

2. AttachGateway → connects that door to your VPC 🏠

3. RouteTable → defines which traffic goes where (the “roadmap”) 🗺️

4. PublicRoute → says: “If traffic goes to the internet (0.0.0.0/0), send it through the gateway.” 🚦

5. Subnet Associations (RouteAssoc1 & 2) → link your subnets to that route table so they can use the internet.

🌍 1️⃣ Internet Gateway

InternetGateway:
  Type: AWS::EC2::InternetGateway

💬 Explanation

• Creates an Internet Gateway (IGW) — think of it as the main door between your AWS VPC and the Internet.

• Without this, your VPC is like an island with no bridge — it can’t send or receive internet traffic.

✅ Purpose:
Provides your VPC access to the public internet.

🧠 Analogy:

Internet Gateway = Broadband router of your AWS home.

🔗 2️⃣ Attach the Gateway to the VPC

AttachGateway:
  Type: AWS::EC2::VPCGatewayAttachment
  Properties:
    VpcId: !Ref MyVPC
    InternetGatewayId: !Ref InternetGateway

💬 Explanation

• Just creating an IGW doesn’t automatically attach it — it’s a separate step.

• This resource attaches the InternetGateway you created to your MyVPC.

✅ Purpose:
Connects the “door” (IGW) to your “house” (VPC), allowing traffic to flow through.

🗺️ 3️⃣ Route Table

RouteTable:
  Type: AWS::EC2::RouteTable
  Properties:
    VpcId: !Ref MyVPC

💬 Explanation

• A Route Table is like a map that defines where network traffic should go.

• Each subnet must be associated with one.

• Since you’re making a public route table, it will contain a route to the internet via the IGW.

✅ Purpose:
Holds routing rules for your subnets.

🧠 Analogy:

Route Table = Road directory that says “traffic to this destination → go through this path.”

🚦 4️⃣ Public Route (Internet Access Rule)

PublicRoute:
  Type: AWS::EC2::Route
  DependsOn: AttachGateway
  Properties:
    RouteTableId: !Ref RouteTable
    DestinationCidrBlock: 0.0.0.0/0
    GatewayId: !Ref InternetGateway

💬 Explanation

• This adds a route entry to your route table.

• DestinationCidrBlock: 0.0.0.0/0 means “any IP address anywhere in the world.”

• GatewayId: !Ref InternetGateway means “send that traffic to the Internet Gateway.”

• DependsOn: AttachGateway ensures that the gateway is attached before this route is created.

✅ Purpose:
Makes all outgoing traffic from your subnets (like ECS containers or EC2 instances) go through the Internet Gateway to reach the internet.

🧠 Analogy:

This is the rule that says “If you’re leaving the neighborhood, use the main highway (Internet Gateway).”

🕸️ 5️⃣ Associate Route Table with Subnet 1

RouteAssoc1:
  Type: AWS::EC2::SubnetRouteTableAssociation
  Properties:
    SubnetId: !Ref Subnet1
    RouteTableId: !Ref RouteTable

💬 Explanation

• This binds Subnet 1 with your Route Table.

• Meaning: Subnet 1 will follow the routes defined there (including internet access).

✅ Purpose:
Gives Subnet 1 access to the internet through the Internet Gateway.

🕸️ 6️⃣ Associate Route Table with Subnet 2

RouteAssoc2:
  Type: AWS::EC2::SubnetRouteTableAssociation
  Properties:
    SubnetId: !Ref Subnet2
    RouteTableId: !Ref RouteTable

💬 Explanation

• Same logic as above, but for Subnet 2.

• So both subnets (in two different Availability Zones) share the same public route table and have internet connectivity.

✅ Purpose:
Ensures Subnet 2 also has public internet access.

🌐 ✅ END RESULT — What You’ve Built

🧭 Visual Summary

Here’s what your network looks like now:

                 🌍 Internet
                     │
             ┌─────────────────┐
             │ Internet Gateway │
             └──────┬───────────┘
                    │
        ┌───────────────────────────────┐
        │           VPC (10.0.0.0/16)   │
        │                               │
        │   ┌────────────────────┐      │
        │   │  Subnet 1 (AZ A)   │────┐ │
        │   │ 10.0.1.0/24        │    │ │
        │   └────────────────────┘    │ │
        │                             │ │
        │   ┌────────────────────┐    │ │
        │   │  Subnet 2 (AZ B)   │────┘ │
        │   │ 10.0.2.0/24        │      │
        │   └────────────────────┘      │
        │                               │
        │   Route Table: 0.0.0.0/0 → IGW│
        └───────────────────────────────┘

💡 TL;DR Summary