Guides

How to Set Up an AWS Application Load Balancer for Two EC2 Servers

By Ravindra Bagale, AWS & DevOps trainer · LinkedIn · Published: 29 September 2026 · Last updated: 30 September 2026

To put an Application Load Balancer (ALB) in front of two EC2 web servers, create a target group (type Instances, HTTP 80, health check path /) and register both instances, then create an internet-facing Application Load Balancer in at least two Availability Zones with a security group that allows HTTP 80 from anywhere and a listener on HTTP 80 that forwards to the target group. Allow port 80 on the instances only from the ALB's security group. When both targets show healthy, open the ALB's DNS name: requests are shared between the two servers.

1. Launch 2 × Amazon Linux 2023 with Nginx, in 2 different AZs (user data below)
2. Security groups:  alb-sg  = inbound HTTP 80 from 0.0.0.0/0
                     web-sg  = inbound HTTP 80 from alb-sg, SSH 22 from My IP
3. EC2 → Target groups → Create → Instances, HTTP 80, health check "/" → register both
4. EC2 → Load balancers → Create → Application Load Balancer → Internet-facing,
   2 AZs, alb-sg, Listener HTTP:80 → forward to the target group
5. Wait for "healthy", then:  for i in 1 2 3 4 5 6; do curl -s http://<ALB-DNS-NAME>; done

What do I need before creating a load balancer?

• An AWS account with the default VPC (it has one public subnet in each Availability Zone).
• Basic EC2 skills: How to Launch an EC2 Instance in AWS and How to Install Nginx on Amazon Linux 2023.
• About 30 minutes. An ALB is not free: it is charged per hour plus usage, so delete it after the lab (Step 7).

How does an ALB share traffic between two servers?

The visitor never talks to the servers directly. The ALB receives every request, sends it to a healthy target (round robin by default), and returns the answer. A health check asks each server for / every few seconds; a server that stops answering gets no traffic until it recovers.

How do I set up an Application Load Balancer for two EC2 servers?

Step 1 — Create the two security groups

EC2 → Security Groups → Create security group:

Create alb-sg first, so you can choose it as the source in web-sg.

Step 2 — Launch two web servers in two Availability Zones

Launch an Amazon Linux 2023 instance with web-sg, and in Network settings → Edit choose a subnet in, for example, ap-south-1a. Under Advanced details → User data paste:

#!/bin/bash
yum install -y nginx
echo "<h1>Server 1 – $(hostname -f)</h1>" > /usr/share/nginx/html/index.html
service nginx start
systemctl enable nginx

Launch the second instance the same way in another zone (for example ap-south-1b) and change Server 1 to Server 2. User data runs once as root at the first boot, so no sudo is needed there.

Step 3 — Check each server on its own

SSH into each instance and confirm Nginx answers locally:

curl -s http://localhost        # <h1>Server 1 – ip-172-31-...</h1>
sudo service nginx status

Because web-sg only allows port 80 from the ALB, the public IP of a server will not open in your browser. That is correct and secure.

Step 4 — Create the target group

EC2 → Target groups → Create target group → target type Instances → name web-tg → protocol HTTP, port 80 → your VPC → health check protocol HTTP, path / → Next. Tick both instances → Include as pending below → Create target group.

Step 5 — Create the Application Load Balancer

EC2 → Load balancers → Create load balancer → Application Load Balancer → Create:

Click Create load balancer. The state goes from Provisioning to Active in a few minutes.

Step 6 — Test that traffic is split

Target groups → web-tg → Targets: wait until both show healthy. Copy the ALB DNS name (for example web-alb-1234567890.ap-south-1.elb.amazonaws.com) and run from your laptop:

for i in 1 2 3 4 5 6; do curl -s http://web-alb-1234567890.ap-south-1.elb.amazonaws.com; echo; done

You see Server 1 and Server 2 taking turns. Now stop Nginx on one server (sudo service nginx stop): after a few failed health checks that target becomes unhealthy and every request goes to the other server — the site stays up. ⚖️ Start Nginx again and it comes back.

For your own domain, point a CNAME (for example www) to the ALB DNS name. Do not use the ALB's IP addresses; they change.

Step 7 — Clean up after the lab

Delete in this order: the load balancer, then the target group, then terminate both instances, and finally the two security groups. The ALB keeps charging every hour until it is deleted.

How do I fix common load balancer problems?

Ghabru naka 😅 — these are the usual ones: