fargate-auto-scaled-backend

A load balanced and auto-scaled api running on AWS ECS.

ci

Init workflow - manual trigger

1. ecs-check Query AWS for existing of service [obtain current task arn].
2. ecr Apply ECR and vpc endpoints.
3. build/image [if service doesn't exist] Push a new initial image to ecr.
4. build/task [if service doesn't exist] Create a new task definition is created.
5. setup/service Apply ecs service, load balancer, deploy and auto-scaling.
6. setup/network Apply vpc link and api gateway ingress.
7. test Basic check on the API /host endpoint.

Deploy workflow - push on main trigger

1. code/image Build image if changes to src/* detected.
2. code/task Apply task definition (no changes if the same image).
3. check Create a deploy boolean based on a new task definition (difference to current) detected.
4. deploy [if deploy=true] Codedeploy deployment is created and status is monitored.
5. A blue/green deployment takes place.

Destroy workflow - manual trigger

1. service Destroy ecs service, load balancer, deploy and auto-scaling resources.
2. network Destroy vpc link and api gateway ingress resources.
3. task Destroy task definition.
4. ecr Destroy ecr and images.

usage

• obtain url from terraform - found in github action init / setup / network outputs
• curl [url]/dev/host

{
    "message":"Request handled by backend at 2024-09-25T12:28:17.593Z",
    "imageUri":"700011111111.dkr.ecr.eu-west-2.amazonaws.com/fargate-auto-scaled-backend@sha256:78dfc01946306dd6afea2b47b56e196788501bfa93c1b2ee1e90a54e72b56938",
    "hostname":"ip-10-55-161-195.eu-west-2.compute.internal"
}

cpu autoscaling

ECS will auto-scale when CPU reaching upper and lower limits. CPU is for entire ECS service.

Initially, the scale-down-alarm cloudwatch alarm state will be In Alarm as CPU will be < scale down threshold. This is expected.

Simulate a load on the ECS service with curl [URL]/dev/stress-cpu/75/120. This example will run 75% CPU load for 120 seconds.

After that load has completed and the =< 1 minute cool off period. This will trigger a cloudwatch alarm which will in turn trigger the auto-scaling rule(s).

Once that load has finished - after the 120 seconds - the scale down alarm will be triggered and the tasks scaled back down.

setup

In tf/service the below variables are to be considered.

• cpu_scale_up_threshold: percentage CPU load to trigger a scale up of tasks.

• cpu_scale_down_threshold: percentage CPU load to trigger a scale down of tasks.

• max_scaled_task_count: maximum amount of tasks to be allowed.

docker

docker build -t express-app .
docker run -i -e BASE_PATH=dev -p 3000:3000 express-app

terraform

Required deployment iam privileges.

[
    "dynamodb:*", 
    "s3:*", 
    "ecr:*", 
    "iam:*", 
    "ecs:*",
    "ec2:*", 
    "elasticloadbalancing:*",
    "application-autoscaling:*",
    "logs:*",
    "cloudwatch:*",
    "apigateway:*",
    "codedeploy:*"
]

ci config

Required github action variables.

• AWS_ACCOUNT_ID
• AWS_REGION
• AWS_ROLE role with above deployment privileges