Route tables configuration in AWS - Step-by-Step Execution

Process Flow - Route tables configuration

Create VPC

↓

Create Subnets

↓

Create Route Table

↓

Add Routes to Route Table

↓

Associate Route Table with Subnet

↓

Traffic follows routes for subnet

This flow shows how to create a route table, add routes, and associate it with a subnet so traffic knows where to go.

Execution Sample

AWS

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

resource "aws_subnet" "subnet1" {
  vpc_id = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
}

resource "aws_internet_gateway" "igw" {
  vpc_id = aws_vpc.main.id
}

resource "aws_route_table" "rt" {
  vpc_id = aws_vpc.main.id
}

resource "aws_route" "route1" {
  route_table_id = aws_route_table.rt.id
  destination_cidr_block = "0.0.0.0/0"
  gateway_id = aws_internet_gateway.igw.id
}

resource "aws_route_table_association" "a" {
  subnet_id = aws_subnet.subnet1.id
  route_table_id = aws_route_table.rt.id
}

This code creates a VPC, a route table, adds a route to the internet gateway, and associates the route table with a subnet.

Process Table

Step	Action	Resource Created/Modified	State Change	Result
1	Create VPC	aws_vpc.main	VPC with CIDR 10.0.0.0/16 created	VPC ready for subnets
2	Create Route Table	aws_route_table.rt	Route table linked to VPC created	Route table ready for routes
3	Add Route	aws_route.route1	Route to 0.0.0.0/0 via IGW added	Route table can send traffic to internet
4	Associate Route Table	aws_route_table_association.a	Route table associated with subnet1	Subnet1 uses this route table
5	Traffic Flow	N/A	Subnet1 traffic follows route table routes	Subnet1 can reach internet via IGW
6	End	N/A	All resources created and linked	Configuration complete

💡 All steps completed; route table configured and associated with subnet

Status Tracker

Resource	Initial	After Creation	After Route Added	After Association	Final
VPC	None	10.0.0.0/16 created	No change	No change	10.0.0.0/16 active
Route Table	None	Created linked to VPC	Route to 0.0.0.0/0 added	Associated with subnet1	Active with routes and association
Route	None	None	Route to internet gateway added	No change	Active route to IGW
Subnet Association	None	None	None	Route table associated	Subnet1 uses route table

Key Moments - 3 Insights

Why do we need to associate a route table with a subnet?

Because without association, the subnet does not know which routes to use. See execution_table step 4 where association links the route table to subnet1.

What happens if we add a route but do not associate the route table with any subnet?

The route exists but no subnet uses it, so traffic from subnets will not follow that route. This is shown by the absence of association in step 4.

Can a route table have multiple routes?

Yes, route tables can have many routes directing traffic to different destinations. Here we added one route in step 3, but more can be added similarly.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the route to the internet gateway added?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'Action' and 'Result' columns in execution_table row for step 3.

According to variable_tracker, what is the state of the route table after association?

A Created but no routes

B Associated with subnet but no routes

C Has routes and associated with subnet

D No association or routes

💡 Hint

Look at the 'Route Table' row under 'After Association' in variable_tracker.

If we skip step 4 (association), what will be the result for subnet1 traffic?

A Subnet1 traffic will not use the route table routes

B Subnet1 traffic will follow the route table routes

C Subnet1 will have internet access anyway

D Subnet1 will be deleted

💡 Hint

Refer to key_moments question about association importance and execution_table step 4.

Concept Snapshot

Route tables control where subnet traffic goes.
Create a route table in your VPC.
Add routes to direct traffic (e.g., to internet gateway).
Associate the route table with subnets.
Subnets use associated route tables to send traffic.
Without association, routes are ignored.

Full Transcript

This visual execution shows how to configure route tables in AWS. First, a VPC is created with a CIDR block. Then a route table is created and linked to the VPC. Next, a route is added to the route table directing traffic to the internet gateway. After that, the route table is associated with a subnet so that subnet's traffic follows the routes. Finally, traffic from the subnet can reach the internet via the route table. Key points include the necessity of associating route tables with subnets and that routes only take effect when associated. The execution table and variable tracker show each step and resource state changes clearly.