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Problem :

I am new to AWS and trying to configure ELB with EC2 in AWS but I ran into "Instance has failed at least the Unhealthy Threshold number of health checks consecutively" error to make the instance out of service. I have also checked following:

1) Currently I am using 8080 port for security check and the path is "/index.html". I have tested the following link http://ec2DNSname:8080/index.html in my browser and it returns following:

Response header:
HTTP/1.1 200 OK
X-Powered-By: Express
Accept-Ranges: bytes
ETag: "150-1420697739000"
Date: Thu, 08 Jan 2015 06:16:21 GMT
Cache-Control: public, max-age=0
Last-Modified: Thu, 08 Jan 2015 06:15:39 GMT
Content-Type: text/html; charset=UTF-8
Content-Length: 150
Vary: Accept-Encoding
Connection: keep-alive

2) In my EC2 configuration I am allowing the inbound TCP traffic on 8080 from any machines

May I know the possible cause of failing the health check?

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1 Answer

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Solution :

If the page is returning a 200 response, it should pass the health check. The Health Check configuration should have the number of times a Health Check needs to return a good result and how often to check it. So for Healthy count of 5 with a check every 30 seconds would only take 2.5 minutes to return as Healthy.

If your HTTP health check is failing then you can try the a TCP health check on port 8080.

Also please check that your VPC configuration is allowing a connection from the Load Balancer to the EC2 instance. This will happen automatically if they belong to the same Subnet, but Network ACLs can impact the connection between different Subnets.

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