Terraform Provisioner: Wait For ECS To Register With LB Before Destroying

main.tf

# Ref: https://github.com/terraform-providers/terraform-provider-aws/pull/3485#issuecomment-397918310


resource "aws_ecs_service" "web" {
  name = "web_service_${var.environment}_${replace(timestamp(), ":", "-")}"
  cluster = aws_ecs_cluster.web.id
  task_definition = aws_ecs_task_definition.web.arn
  desired_count = 1
  force_new_deployment = true

  load_balancer {
    target_group_arn = data.aws_lb_target_group.web_ecs_arn.arn
    container_name = "web"
    container_port = 8000
  }

  # Important! Wait till services are up and running before destroying
  provisioner "local-exec" {
    command = "aws ecs wait services-stable --services ${aws_ecs_service.web.name} --cluster ${aws_ecs_cluster.web.name} --region ${data.aws_region.current.name}"
  }

  provisioner "local-exec" {
    command = "aws elbv2 wait target-in-service --target-group-arn ${data.aws_lb_target_group.web_ecs_arn.arn} --region ${data.aws_region.current.name}"
  }

  lifecycle {
    create_before_destroy = true
  }
}

terraform {
  required_version = ">= 0.13, < 0.14"

  required_providers {
    null = {
      source = "hashicorp/null"
      version = "2.1.2"
    }
  }
}

provider "null" {}

// ...

resource "null_resource" "wait_for_service_deploy" {
  triggers = {
    task_definition = aws_ecs_service.web.task_definition
  }

  provisioner "local-exec" {
    command = "aws ecs wait services-stable --services ${aws_ecs_service.web.name} --cluster ${aws_ecs_cluster.web.name} --region ${data.aws_region.current.name}"
  }
}


resource "null_resource" "wait_for_service_lb_healthy" {
  triggers = {
    task_definition = aws_ecs_service.web.task_definition
    service_stable = null_resource.wait_for_service_deploy.id
  }

  provisioner "local-exec" {
    command = "aws elbv2 wait target-in-service --target-group-arn ${data.aws_lb_target_group.web_ecs_arn.arn} --region ${data.aws_region.current.name}"
  }
}

resource "null_resource" "wait_for_service_deploy" {
  triggers = {
    ecs_service = aws_ecs_service.web.name
  }

  provisioner "local-exec" {
    command = "aws ecs wait services-stable --services ${aws_ecs_service.web.name} --cluster ${aws_ecs_cluster.web.name} --region ${data.aws_region.current.name}"
  }
}


resource "null_resource" "wait_for_service_lb_healthy" {
  triggers = {
    ecs_service = aws_ecs_service.web.name
    service_stable = null_resource.wait_for_service_deploy.id
  }

  provisioner "local-exec" {
    command = "aws elbv2 wait target-in-service --target-group-arn ${data.aws_lb_target_group.web_ecs_arn.arn} --region ${data.aws_region.current.name}"
  }
}