Traffic Management with AWS Load Balancers

Here are the steps to manage traffic effectively using an AWS Elastic Load Balancer:

1. Choose the Right Load Balancer
The first step in managing traffic is selecting the right type of load balancer:
Use an Application Load Balancer (ALB) if you need:
Path-based or host-based routing (e.g., example.com/app1 routes to one set of targets, example.com/app2 to another).
WebSocket support or HTTP/2 traffic.
Load balancing for containerized or microservice architectures (like ECS or EKS).

Use a Network Load Balancer (NLB) if:
You require low-latency TCP or UDP connections.
You need to handle a very large volume of traffic.

Use a Gateway Load Balancer (GWLB) for:
Directing traffic through third-party network appliances, such as firewalls, IDS/IPS systems.

2. Configure Target Groups
A target group defines how the load balancer routes requests to backend instances. For example, in an Application Load Balancer:
Targets: These can be EC2 instances, IP addresses, or Lambda functions.
Routing rules: Define how incoming traffic is distributed. You can route traffic based on:
Paths: e.g., /api/* routes traffic to your API services.
Hosts: e.g., app.example.com routes to one microservice, and admin.example.com routes to another.

For an NLB, target groups usually consist of IP addresses or EC2 instances that handle TCP/UDP traffic.
resource
`"aws_lb_target_group" "app" {
name = "app-target-group"
port = 80
protocol = "HTTP"
vpc_id = var.vpc_id

health_check {
path = "/health"
interval = 30
timeout = 5
healthy_threshold = 3
unhealthy_threshold = 2
}
}`

3. Create Listeners for Routing
Listeners are processes that check for incoming connection requests and route traffic to appropriate targets based on defined rules. For ALBs, listeners are typically configured for HTTP/HTTPS (ports 80 and 443), while NLB listeners might be for TCP/UDP traffic.
You can set up path-based or host-based routing by specifying listener rules in the Application Load Balancer. For example, for path-based routing:
resource
`"aws_lb_listener" "app_listener" {
load_balancer_arn = aws_lb.app_lb.arn
port = 80
protocol = "HTTP"
default_action {
type = "forward"
target_group_arn = aws_lb_target_group.app.arn
}
}

resource "aws_lb_listener_rule" "path_based_routing" {
listener_arn = aws_lb_listener.app_listener.arn
priority = 100
action {
type = "forward"
target_group_arn = aws_lb_target_group.api.arn
}
condition {
field = "path-pattern"
values = ["/api/"]
}
}`
Here, /api/ requests are routed to the API target group.

4. Configure Health Checks
Health checks monitor the status of your targets. If a target becomes unhealthy, the load balancer will stop sending traffic to it until it recovers.
For an Application Load Balancer:
health_check {
path = "/status"
interval = 30
timeout = 5
healthy_threshold = 3
unhealthy_threshold = 2
matcher = "200-299"
}
The load balancer continuously checks the health of targets by sending requests to the specified path (e.g., /status) and only routes traffic to healthy targets.

5. Enable Cross-Zone Load Balancing
Cross-Zone Load Balancing ensures that traffic is distributed evenly across targets in different Availability Zones, increasing fault tolerance.
In Terraform, you can enable cross-zone load balancing like this:
resource
"aws_lb" "app_lb" {
name = "app-lb"
internal = false
load_balancer_type = "application"
enable_cross_zone_load_balancing = true
security_groups = [aws_security_group.lb_sg.id]
subnets = aws_subnet.subnet_ids
}
This ensures that traffic is evenly distributed across all targets in all Availability Zones.

6. Auto Scaling Integration
AWS Load Balancers integrate with Auto Scaling Groups to dynamically add or remove instances based on traffic demand. The Auto Scaling Group ensures that healthy instances are automatically registered with the load balancer.
Here's an example of integrating an Application Load Balancer with an Auto Scaling Group:
resource
`"aws_autoscaling_group" "app_asg" {
desired_capacity = 2
max_size = 5
min_size = 1
vpc_zone_identifier = [aws_subnet.subnet_ids]
target_group_arns = [aws_lb_target_group.app.arn]

lifecycle {
create_before_destroy = true
}
}`
As traffic increases, the Auto Scaling Group will launch new instances and automatically register them with the load balancer, ensuring that your application can scale to handle the load.

7. SSL/TLS Termination
For secure HTTPS traffic, AWS load balancers can handle SSL termination. You can configure an SSL certificate for HTTPS traffic and offload the decryption to the load balancer, reducing the load on backend instances.
resource
`"aws_lb_listener" "https_listener" {
load_balancer_arn = aws_lb.app_lb.arn
port = 443
protocol = "HTTPS"
ssl_policy = "ELBSecurityPolicy-2016-08"
certificate_arn = aws_acm_certificate.app_cert.arn

default_action {
type = "forward"
target_group_arn = aws_lb_target_group.app.arn
}
}`

Conclusion
AWS Load Balancers provide powerful features for managing traffic across multiple instances or services, ensuring high availability, scalability, and security. Whether you need advanced routing with an Application Load Balancer or ultra-low latency with a Network Load Balancer, AWS provides the tools you need to manage traffic effectively.
By integrating features like Auto Scaling, SSL termination, health checks, and cross-zone load balancing, you can optimize your application's performance, reliability, and security.
With this understanding, you can confidently manage traffic for a range of scenarios using AWS Elastic Load Balancers!