The 502 Bad Gateway error is one of the most common issues encountered when deploying web applications on Elastic Beanstalk. This error occurs when the Elastic Beanstalk proxy server (Nginx) is unable to establish a connection to the application backend, which in our case is the Node.js server. Below, I explain how this error manifests itself, how to investigate it using Nginx logs, and the solutions applied to resolve connection problems on port 8080.
The 502 Bad Gateway message basically indicates that Nginx is unable to communicate properly with the Node.js application. This can be caused by a number of issues, such as:
Node.js process is not running : If Node.js is not direct moving leads email list running properly, Nginx will not be able to route requests.
The application port is not set correctly – Elastic Beanstalk expects the Node.js application to be listening on a specific port (usually port 8080).
Nginx Configuration Path Issues: The default Nginx configuration on Elastic Beanstalk can have issues if it is not properly aligned with your application.
Investigating 502 error using Nginx logs
The first step in diagnosing a 502 error is to review the Nginx logs. In Elastic Beanstalk, you can access the Nginx logs by running the following command from the EB CLI:
eb ssh
sudo tail -f /var/log/nginx/error.log
Here, you will see log entries that may show messages like:
2024/10/17 10:00:00 [error] 32320#32320: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 172.31.8.131, server: , request: "GET / HTTP/ 1.1", upstream host: "my-app-v1.
This error message tells us that Nginx is trying to connect to port 8080 , but cannot because the application is not responding or the port is not open.
Applied solutions to resolve problems with connections to port 8080 in Node.js
Once the problem has been identified in the logs, we move on to the most common solutions that help resolve this type of error:
Check if Node.js is running
The first step is to check if the Node.js server is running on the correct port. To do this, you can connect to the EC2 instance and run the following command:
ps aux | grep node
This should show whether the Node.js process is running correctly. If it doesn't, it means that the application isn't starting, which could be due to a misconfiguration or a problem with dependencies.