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John Heyer
Asked: 2021-07-11 12:59:51 +0800 CST

AWS ALB Shows Target Group unhealthy, even though port 80 is open to Internet

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I've built an AWS ALB & Target group via Terraform and everything looks correct but the Target Group is reporting unhealthy for HTTP, HTTPS, and TCP. The instance is a t3.nano in us-east-2 and has Nginx installed and running.

I've verified the following:

  • Nginx is configured and running on ports 80 & 443
  • Security groups allow HTTP & HTTPS from 0.0.0.0/0
  • Instance is on a public subnet (that is, the 0.0.0.0/0 route is to the IGW)

If I access the instance's public IP from Internet, and the "Welcome to nginx!" page is displayed. This request shows up both in /var/log/nginx/access.log. tcpdump port 80 shows requests coming from Internet but nothing indicating an AWS healthcheck.

I've used ALBs and Target groups before and never encountered an issue like this. The only difference is this instance was created with Terraform.

amazon-ec2 amazon-web-services terraform amazon-alb amazon-elastic-ip

1 Answers

  1. I think you need to configure the target_type parameter in your lb_target_group resource. The default value is instance, that configuration requires use autoscaling_group for EC2 instances. If you use aws_instance for EC2, you need use ip parameter.

    https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lb_target_group#target_type

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