AWS ALB Health Check for multiples app or services on NGINX

There are many reasons to deploy multiple apps or services on a NGINX AWS EC2 instance, from cost savings to redundancy. In our case, we have an Application Load Balancer handling all requests to a Target Group (or Server Farm). However, in those cases is not just straightforward to set up the targets health check.

This post presents a solution to that scenario.

Case

Our EC2 Instance has a default website on port 80 and 2 or more apps on port 80 but with different host headers (ie: aka.mydomain.com, afa.mydomain.com, etc), so when it is time to set up the Target Group Health Check we need a solution to how to monitor each service (or app) instead of the default NGINX site.

Solution

We ended up changing our default NGIX website (etc/nginx/sites-available/default) by including the following segment:

        location /aka {
                proxy_set_header Host aka.mydomain.com;
                proxy_pass http://127.0.0.1/health;                
        }

        location /afa {
                proxy_set_header Host afa.mydomain.com;
                proxy_pass http://127.0.0.1/health;
        }

Therefore, on each Target Group, we can use on the path of the Health Check “/aka” and in the other Target Group “/afa”. We are doing an NGINX redirect and adding the host header, the health route is a health check page on all our applications that returns 200 and some details of the status of our apps and services.

Now, Our EC2 instance running multiple NGINX apps or services can be a target on both Target Groups and the health check will do its job if one of the services is down sending requests to any other available targets.

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