Troubleshooting 502 Bad Gateway Error in Spring Boot Application on Elastic Beanstalk

Based on the information provided, there are several potential reasons for the 502 Bad Gateway error you're encountering with your Spring Boot application on Elastic Beanstalk. Here are some key areas to investigate:

1. Database Connection: While you've successfully connected to the RDS MySQL database locally, ensure that the application.properties file in your deployed application contains the correct database URL, username, and password for the RDS instance. The connection details might need to be updated for the production environment.

2. Security Group Configuration: You've added a security group for RDS and associated it with your Elastic Beanstalk environment. Make sure that this security group allows inbound traffic on the MySQL port (typically 3306) from the security group associated with your Elastic Beanstalk instances.

3. Application Port: You've set server.port to 5000 in your application.properties file. Ensure that your Elastic Beanstalk environment is configured to forward traffic to this port. You may need to add a configuration file (e.g., .ebextensions/nginx-proxy.config) to your project to tell Elastic Beanstalk to proxy requests to port 5000.

4. Health Checks: Verify that your application has a health check endpoint (e.g., "/actuator/health" or a custom endpoint) that Elastic Beanstalk can use to determine if your application is running correctly.

5. Environment Variables: Check if any crucial environment variables are missing in your Elastic Beanstalk environment configuration. These might include database credentials or other application-specific settings.

6. Application Logs: Access the logs for your Elastic Beanstalk environment to look for any error messages or exceptions that might be causing the application to fail to start or respond properly.

7. Memory/CPU Issues: Ensure that your application has sufficient resources allocated. If the application is running out of memory or CPU, it might fail to respond, leading to a 502 error.

8. Nginx Configuration: Since you're seeing a nginx error, there might be an issue with the nginx configuration. Check the nginx error logs (/var/log/nginx/error.log) on the EC2 instance for more detailed error messages.

To troubleshoot further:

• SSH into the EC2 instance and check application logs in /var/log/web.stdout.log for any startup errors.
• Verify that your application is actually running and listening on port 5000 using commands like 'ps aux' and 'netstat -tulpn'.
• Try to curl your application directly from the EC2 instance (e.g., curl http://localhost:5000) to see if it responds.

If after checking these areas you're still encountering issues, you may need to review your application code for any environment-specific configurations that might be causing problems in the Elastic Beanstalk environment.
Sources
502 Bad Gateway on a Spring boot application in elastic beanstalk | AWS re:Post
502 Bad Gateway on AWS Elastic Beanstalk with Java Spring Boot App and RDS database (Postgres) | AWS re:Post
502 Bad Gateway when going from Single Instance to Load Balancer in Elastic Beanstalk | AWS re:Post
How to debug 502 errors on ELB | AWS re:Post
Elastic Beanstalk | AWS re:Post

Hi,

Even if you issue may be different, this article give a very detailled step-by-step analysis method for Bad Gateway errors with EBs: https://jaxlondon.com/blog/troubleshooting-http-502-bad-gateway-in-aws-ebs/

This video may also be helpful: https://www.youtube.com/watch?v=7Ng0iquExjs

Best,

Didier