Module 12, AWS Compute with Terraform

Elastic Beanstalk

resource "aws_elastic_beanstalk_application" "app" {
  name        = var.app_name
  description = "FinPay application"
}

resource "aws_elastic_beanstalk_environment" "production" {
  name                = "${var.app_name}-production"
  application         = aws_elastic_beanstalk_application.app.name
  solution_stack_name = "64bit Amazon Linux 2023 v4.3.0 running Docker"

  setting {
    namespace = "aws:autoscaling:asg"
    name      = "MinSize"
    value     = "2"
  }

  setting {
    namespace = "aws:autoscaling:asg"
    name      = "MaxSize"
    value     = "4"
  }

  setting {
    namespace = "aws:elasticbeanstalk:environment"
    name      = "LoadBalancerType"
    value     = "application"
  }

  setting {
    namespace = "aws:elasticbeanstalk:healthreporting:system"
    name      = "SystemType"
    value     = "enhanced"
  }
}

Deployment Policies (Exam Critical)

Policy	Downtime	Speed	Rollback
All at once	Yes	Fastest	Re-deploy old version
Rolling	No	Medium	Re-deploy old version
Rolling with additional batch	No	Slowest	Re-deploy old version
Immutable	No	Slow	Terminate new instances ✅
Blue/Green	No	Slow	Swap CNAME back ✅

setting {
  namespace = "aws:elasticbeanstalk:command"
  name      = "DeploymentPolicy"
  value     = "Immutable"   # safest for production
}

ECS Fargate

resource "aws_ecs_cluster" "main" {
  name = "${var.app_name}-cluster"
}

resource "aws_ecs_task_definition" "app" {
  family                   = var.app_name
  requires_compatibilities = ["FARGATE"]
  network_mode             = "awsvpc"
  cpu                      = 256
  memory                   = 512
  execution_role_arn       = aws_iam_role.ecs_execution.arn

  container_definitions = jsonencode([{
    name  = var.app_name
    image = "${aws_ecr_repository.app.repository_url}:latest"
    portMappings = [{ containerPort = 3000; protocol = "tcp" }]
    logConfiguration = {
      logDriver = "awslogs"
      options = {
        "awslogs-group"         = "/ecs/${var.app_name}"
        "awslogs-region"        = var.aws_region
        "awslogs-stream-prefix" = "ecs"
      }
    }
  }])
}

resource "aws_ecs_service" "app" {
  name            = var.app_name
  cluster         = aws_ecs_cluster.main.id
  task_definition = aws_ecs_task_definition.app.arn
  desired_count   = 2
  launch_type     = "FARGATE"

  network_configuration {
    subnets          = aws_subnet.private_app[*].id
    security_groups  = [aws_security_group.ecs.id]
    assign_public_ip = false
  }
}

Knowledge Check

1. What is the difference between Immutable and Rolling deployment policies?
2. Which EB deployment policy causes downtime?
3. What does FARGATE launch type mean vs EC2?
4. Why would you use ECS over Elastic Beanstalk?
5. What is the purpose of execution_role_arn in an ECS task definition?

Exam Mapping

• AWS DevOps Pro Domain 1: Deployment strategies, heavily tested