ECS Fargate / single ALB / multiple docker containers - docker

Question

Does anyone have an example of how I could build up an ECS cluster with a single application load balancer forwarding host header request to two different docker containers.
I want to have one ALB for A single ESC cluster running both my angular site as well as a.net web service. Ultimately my goal is to script this in terraform.

Answer 1

Without knowing all the information I think that you are looking for path-based routing or even better host-based routing.
Terraform
You need an aws_lb_listener_rule (Load Balancer Listener Rule) for each host/path.
You need an aws_alb_target_group for each ECS services and you refer the correct target group inside the resource aws_lb_listener_rule.
General
Listener Rules
Before you start using your Application Load Balancer, you must add one or more listeners. A listener is a process that checks for connection requests, using the protocol and port that you configure. The rules that you define for a listener determine how the load balancer routes request to the targets in one or more target groups. docs
Use Path-Based Routing with Your Application Load Balancer
https://docs.aws.amazon.com/en_us/elasticloadbalancing/latest/application/tutorial-load-balancer-routing.html
Examples
Host Based Listener Rule
resource "aws_lb_listener_rule" "host_based_routing" {
listener_arn = aws_lb_listener.front_end.arn
priority = 99
action {
type = "forward"
target_group_arn = aws_lb_target_group.static.arn
}
condition {
field = "host-header"
values = ["my-service.*.terraform.io"]
}
}
Where the conditions block define the host or the pattern (example below) where request must be sent.
Path Based Listener Rule
resource "aws_lb_listener_rule" "static" {
listener_arn = aws_lb_listener.front_end.arn
priority = 100
action {
type = "forward"
target_group_arn = aws_lb_target_group.static.arn
}
condition {
field = "path-pattern"
values = ["/static/*"]
}
}
Target group
resource "aws_alb_target_group" "alb_target_group" {
name = "example-target-group"
protocol = "HTTP"
port = var.exposed_port
vpc_id = var.vpc_id
deregistration_delay = 30
health_check {
path = var.service_health_check_path
matcher = "200-399"
}
}
https://www.terraform.io/docs/providers/aws/r/lb_listener_rule.html
https://www.terraform.io/docs/providers/aws/r/lb_target_group.html