502 Bad Gateway on EC2

Question

Last week an application hosted on aws ec2 started responding with a 502 bad gateway error. Nothing changed about the files hosted or any of the settings of the instance that should cause this. In fact you can brute force log in to the application if you have the patience to keep reloading the address. I do not know how to begin to address this situation.

Answer

Two possibilities:

If you're running a load balancer then it will return a 502 error to the client if the instance(s) in your target group(s) are not available.

If you're running a single instance then a 502 error means that you've connected successfully to the instance but the web server software (Apache, IIS, etc) is not configured correctly. In this case, if it is intermittent then there is some issue on the instance itself. Check the log files and see what is happening.

502 Bad Gateway on EC2

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