Troubleshooting NGINX Reverse Proxy Errors in Kubernetes

In a Kubernetes environment, NGINX serves as the "front door" to your microservices. While it is a powerful tool, it introduces layers of complexity that can make debugging a challenging experience. When users encounter a "502 Bad Gateway" error, the underlying issue could stem from the Ingress, the Service, or the Pod itself. In this guide, we will explore effective strategies to trace and resolve these failures.

The Error: 502 Bad Gateway

A 502 Bad Gateway error typically indicates that NGINX (the Ingress) attempted to connect to your application but was unable to establish a valid connection. To diagnose this issue, start by checking the "Endpoints" of your service. If your application has not successfully passed its Liveness or Readiness Probes, Kubernetes will exclude it from the service rotation, leaving NGINX without a destination for incoming traffic.

kubectl get endpoints [service-name]

The Error: 504 Gateway Timeout

In contrast, a 504 Gateway Timeout error suggests that the application was indeed found, but it did not respond within the expected timeframe. This scenario is common among Node.js applications that are performing heavy data processing or waiting on slow database queries. To resolve this, you may need to increase the NGINX proxy timeout settings in your Ingress annotations. Consider adjusting the following setting:

nginx.ingress.kubernetes.io/proxy-read-timeout: "600"

Implementing an Effective Logging Strategy

When troubleshooting, it is crucial to review more than just the application logs. You should also examine the Ingress Controller logs, as they provide specific upstream response codes that can pinpoint the exact location of the failure during the handshake process. Utilize the following command to access real-time traffic flow and identify which microservice may be causing issues:

kubectl logs -n ingress-nginx [pod-name]