API Gateway

Architecture

Deploy an ALB as a lightweight API gateway:

Single entry point for all API traffic
Route to services based on path prefixes
SSL termination at the load balancer
Health monitoring with automatic failover

When to Use

Use ALB as an API gateway when:

You need simple path-based routing without advanced features
Cost is a concern (cheaper than API Gateway)
You want direct integration with ECS or EC2 targets
You do not need request transformation or throttling

Example Configuration

module "api_gateway_alb" {
  source  = "registry.patterneddesigns.ca/patterneddesigns/alb/aws"
  version = "3.0.0"

  name    = "api-gateway"
  vpc_id  = module.vpc.vpc_id
  subnets = module.vpc.public_subnets

  https_listeners = [{
    port            = 443
    certificate_arn = aws_acm_certificate.api.arn
  }]

  listener_rules = [
    {
      priority   = 100
      conditions = [{ path_pattern = ["/users/*"] }]
      actions    = [{ type = "forward", target_group_arn = aws_lb_target_group.users.arn }]
    },
    {
      priority   = 200
      conditions = [{ path_pattern = ["/orders/*"] }]
      actions    = [{ type = "forward", target_group_arn = aws_lb_target_group.orders.arn }]
    },
    {
      priority   = 300
      conditions = [{ path_pattern = ["/products/*"] }]
      actions    = [{ type = "forward", target_group_arn = aws_lb_target_group.products.arn }]
    }
  ]
}

Considerations

ALB does not provide request throttling (use WAF rate limiting)
No built-in request/response transformation
Works well with ECS Fargate and Lambda targets