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Route Tables

We've attached an internet gateway to our VPC, but nothing tells the subnets it exists or when to use it.

To do that we need a route, and routes live in the creatively named route table. It is literally just a list of routes.

We can add a special kind of route, a "default route," to our table. It is a catch-all rule that says:

"If you don't have a specific address for something, look here."

This lets us create rules for things we care about (like local traffic). If we don't have a specific rule for something, we send it to the internet. When we're done with this lesson, our VPC will look like this:

Assignment

Create a route table that sends public subnet traffic to the internet gateway.

Navigate to "VPC" using the search bar in the AWS Console.
Click on "Route tables" in the left-hand menu.
Click the orange "Create route table" button at the top right.
Name the new route table patientping-public-rt, select our patientping VPC, and click "Create route table."
Click the "Actions" dropdown button at the top right, then click "Edit subnet associations."
Select both patientping-public-a and patientping-public-b (and only those!), then click "Save associations."
Back in the list of route tables, select patientping-public-rt again, and click "Actions" → "Edit routes."
Click "Add route."
Set the destination to 0.0.0.0/0. This "everything CIDR" is what makes it the default route.
For the target, select "Internet Gateway." It should open a new input field, where you can select the gateway you just created (patientping-igw).
Click "Save changes."

Whew! Finally, we have "public" subnets that can connect to the internet.

Take a moment to review your "Internet gateways" and "Route tables" in the VPC dashboard.

Run and submit the CLI tests.

Tip

If you want to use the CLI instead, here's the command structure:

# Create a route table
aws ec2 create-route-table --vpc-id <vpc-id> --tag-specifications 'ResourceType=route-table,Tags=[{Key=Name,Value=<name>}]'
# Associate the route table with a subnet (run once per public subnet)
aws ec2 associate-route-table --route-table-id <rt-id> --subnet-id <subnet-id>
# Add a route to the route table
aws ec2 create-route --route-table-id <rt-id> --destination-cidr-block 0.0.0.0/0 --gateway-id <igw-id>