Create the load balancer

A target group with a health check, and an internet-facing Application Load Balancer in front of the API.

About 20 min · Verified 8 October 2026

0 of 9 steps done0%

On this page

Create the target group
Open the wizard
Set the health check
Skip registering targets and create
Shorten the deregistration delay
Create the load balancer
Choose the type
Basic configuration and network mapping
Security group and listener
Wait for Active and save the DNS name
Verify

The Application Load Balancer (ALB) is the only public door to your API. It accepts HTTP on port 80, picks a healthy server from a target group, and forwards the request to port 3000. It keeps asking each server a question (the health check) and stops sending traffic to servers that do not answer.

You will create the target group first, then the load balancer. The server does not exist yet, and that is fine: you register it in the EC2 chapter.

Create the target group#

Open the wizard#

Open EC2Target GroupsCreate target group.

Field	Value
Choose a target type	Instances
Target group name	`shortlink-app-tg`
Protocol : Port	HTTP : `3000`
IP address type	IPv4
VPC	`shortlink-vpc`
Protocol version	HTTP1

Set the health check#

Under Health checks:

Field	Value
Health check protocol	HTTP
Health check path	`/health`

Expand Advanced health check settings:

Field	Value
Port	Traffic port
Healthy threshold	`2`
Unhealthy threshold	`2`
Timeout	`5` seconds
Interval	`10` seconds
Success codes	`200`

/health is a route the API provides. It runs a tiny query against the database and returns 200 {"status":"ok","database":"up"}, or 503 if the database cannot be reached. So a server only counts as healthy if the database connection works too.

Skip registering targets and create#

Choose Next. On Register targets do not select anything. Choose Create target group.

Shorten the deregistration delay#

Open the new target group → Attributes → Edit. Change Deregistration delay from 300 to 30 seconds and save.

Create the load balancer#

Choose the type#

Open EC2Load BalancersCreate load balancer. Under Application Load Balancer choose Create.

Basic configuration and network mapping#

Field	Value
Load balancer name	`shortlink-alb`
Scheme	Internet-facing
Load balancer IP address type	IPv4
VPC	`shortlink-vpc`
Mappings	Tick both Availability Zones and, for each, choose the public subnet (`10.0.1.0/24` and `10.0.2.0/24`)

Security group and listener#

Field	Value
Security groups	Remove `default`, add `shortlink-alb-sg`
Listener protocol : port	HTTP : `80`
Default action	Forward to `shortlink-app-tg`

Choose Create load balancer.

Wait for Active and save the DNS name#

Open the load balancer. State moves from Provisioning to Active in 2 to 3 minutes. Copy DNS name (it looks like shortlink-alb-123456789.<region>.elb.amazonaws.com) into My values → Load balancer DNS name.

Verify#

Your computerAsk the load balancer for /health

curl -i http://<ALB_DNS>/health

Replace <ALB_DNS> with your own value (or fill in the known ones once under My values at the top of the page).

Expected output

HTTP/1.1 503 Service Temporarily Unavailable

A 503 is exactly what you want right now. It proves the load balancer is reachable from the internet and that it has no healthy servers yet.

curl times out or cannot resolve the host

Cannot resolve host: the load balancer may still be provisioning. Wait a minute and retry.
Timeout: the load balancer is in the wrong subnets, or shortlink-alb-sg does not allow port 80 from 0.0.0.0/0. Re-check the mappings and the security group.

Next: the S3 website bucket.

Found a mistake? Edit this page on GitHub.