I'm using ELB to serve a GraphQL API. In conclusion, the choice of which ELB health check protocol is right for you will depend upon the specifics of your application. Healthy machines are given a balanced portion of the traffic being directed through the ELB. ELB health check verifies that a specified TCP port on an instance is accepting connections OR a specified web page returns 2xx code. AWS elastic load balancers and application load balancers are awesome, but their health checks are pretty dumb. you get 302 when performing URL redirection, any ELB Health check will look for success code 200 for the health check to pass. ELB Health Check. To modify the health check settings of a target group using the console. The goal is to GET my node.js app health check URL, and make AWS ELB mark the instance as unhealthy if the health check URL status is not 200. If you’d like the instances to always be added to the ELB regardless of the HTTP response then TCP protocol is the right choice for you. In my case my health check path was /health. Hello, has anyone else seen sporadic health checks failing on their elastic beanstalk applications? If an Auto Scaling group’s health check type is set to ELB, Amazon EC2 Auto Scaling performs both ELB and EC2 health checks and terminates instances that fail either health check: Open the Amazon EC2 console. select the health check tab; make sure the health check for your EC2 instance is the same as the health check in the target group. To automate the replacement of unhealthy EC2 instances, you must change the health check type of your instance's Auto Scaling group from EC2 to ELB by using a configuration file.. Keep the following in mind: In the navigation pane, under Auto Scaling, choose Auto Scaling Groups, and then choose the instance's group. I'm using running the docker configuration on a single t2.micro instance with monitoring interval set for 1 minute. A healthy EC2 instance is one that issues a response to a health check call with a 200 response code. The ELB Health Check is configured with a protocol and port number to call on the target instances. ELB health-check requests use the private IP address of the EC2 instance as the host header so we need to ensure such requests are correctly handled by the Django application. It's not possible to specify any headers (such as the Host header), making it impossible for virtual hosts to be taken into account when determining if the host is healthy or not. /_health/ is also not a great endpoint to use for health checking from a load balancer, which is a separate issue. In ALB, this can be configured under health check in the ELB console. Post upgrade, the following health check, which were were working fine prior to the upgrade, is no longer working. So this was recently brought to our attention in our IRC channel, #sentry, and it turns out, ELB doesn't send a Host header with it's health checks, which is why this fails since we do a strict check based on the system.url-prefix config setting. Thus ELB health checks are a little bit smarter and verify that actual app works instead of verifying that just an instance works. I have also deleted the original ELB and re-created it with the same settings as before the upgrade without any luck. I have attempted to remove the nodes from the original ELB and add them back into it without any luck. The health check is an http/s request to the path you specify. By default, the health check configuration of your Auto Scaling group is set as an EC2 type that performs a status check of EC2 instances. Note that reason codes that begin with Elb originate on the load balancer side and reason codes that begin with Target originate on the target side. 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