Target Groups and Health Checks

Target groups route traffic to tasks and drop ones that fail health checks.

A target group is the set of task IPs the load balancer sends traffic to. For awsvpc tasks the target type must be ip.

Health checks

The target group pings a path (e.g. /health) on each task. A task must pass a number of checks to become healthy and start receiving traffic; consecutive failures mark it unhealthy and it is drained.

ECS uses these results to decide whether a new deployment is stable.

Example

Example · bash
aws elbv2 create-target-group \
  --name web-tg \
  --protocol HTTP --port 80 \
  --vpc-id vpc-0abc123 \
  --target-type ip \
  --health-check-path /health \
  --healthy-threshold-count 2 \
  --unhealthy-threshold-count 3

When to use it

  • An ops engineer sets a longer deregistration delay on the target group so ECS tasks have 60 seconds to finish in-flight requests before being removed from service.
  • A developer adjusts the health check threshold from 5 to 2 consecutive successes so newly deployed tasks are marked healthy and receive traffic faster.
  • A team configures separate target groups for blue and green ECS services to enable a CodeDeploy traffic shift with instant rollback capability.

More examples

Tune Health Check Settings

Tunes the health check to require only 2 consecutive successes before marking a task healthy, reducing the time new tasks wait before receiving traffic.

Example · bash
aws elbv2 modify-target-group \
  --target-group-arn arn:aws:elasticloadbalancing:us-east-1:123456789012:targetgroup/api-tg/abc \
  --health-check-interval-seconds 15 \
  --healthy-threshold-count 2 \
  --unhealthy-threshold-count 3 \
  --health-check-timeout-seconds 5

Set Deregistration Delay

Sets a 60-second deregistration delay so the ALB gives stopping tasks time to finish in-flight requests before removing them from the target group.

Example · bash
aws elbv2 modify-target-group-attributes \
  --target-group-arn arn:aws:elasticloadbalancing:us-east-1:123456789012:targetgroup/api-tg/abc \
  --attributes Key=deregistration_delay.timeout_seconds,Value=60

Check Target Health Status

Lists every registered target (task ENI IP) in the group with its current health state and reason code to diagnose unhealthy tasks quickly.

Example · bash
aws elbv2 describe-target-health \
  --target-group-arn arn:aws:elasticloadbalancing:us-east-1:123456789012:targetgroup/api-tg/abc \
  --query 'TargetHealthDescriptions[*].{ip:Target.Id,port:Target.Port,state:TargetHealth.State,reason:TargetHealth.Reason}' \
  --output table

Related

ecs alb integrationecs health checks

Discussion

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