How to fix 502 Bad Gateway in Kubernetes

KubernetesINTERMEDIATEHIGH

The Ingress controller cannot reach healthy backend pods because they are failing health checks, restarting, or not listening on the expected port. A 502 indicates the gateway received an invalid response from the upstream service, typically due to readiness probe failures, port mismatches, or pods crashing. Fix by ensuring backend pods are healthy and ports match the service configuration.

What this error means

A 502 Bad Gateway error from an Ingress controller (nginx, traefik, etc.) means the Ingress received traffic but couldn't reach a healthy backend pod. The backend service exists but all pods are either not ready (readiness probe failing), crashing, or not listening on the configured port. This differs from 503 (no endpoints) in that endpoints exist but are unhealthy.

How to fix "502 Bad Gateway"

1Check backend pod readiness status

Examine pod readiness:

bash

kubectl get pods -n <namespace> -o wide
kubectl describe pod <pod-name> -n <namespace> | grep -A10 "Conditions"

Look for "Ready" condition. If False, readiness probe is failing. Check:

bash

kubectl describe pod <pod-name> -n <namespace> | grep -A5 "Readiness probe"

2Verify backend pod ports match Ingress service

Check the full port chain:

bash

# Ingress backend service
kubectl get ingress <ingress-name> -n <namespace> -o yaml | grep -A10 "backend:"

# Service port configuration
kubectl get service <service-name> -n <namespace> -o yaml | grep -A5 "ports:"

# Pod listening port
kubectl exec <pod-name> -n <namespace> -- netstat -tlnp | grep LISTEN

All three must align: ingress → service targetPort → pod containerPort.

3Check application logs for errors

Review pod logs:

bash

kubectl logs <pod-name> -n <namespace> --tail=100
kubectl logs <pod-name> -n <namespace> -p  # Previous pod (if crashed)

Look for startup errors, port binding failures, or exceptions.

4Increase readiness probe timeout

If application starts slowly, increase timeouts:

yaml

readinessProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 10  # Increased from 0
  timeoutSeconds: 3        # Increased from 1
  periodSeconds: 5
  failureThreshold: 2

Redeploy and monitor.

5Allocate more resources to pods

Resource starvation causes timeouts and hangs:

bash

kubectl top pod <pod-name> -n <namespace>
kubectl describe node <node-name> | grep -A10 "Allocated resources"

Increase resource requests/limits:

yaml

resources:
  requests:
    cpu: 500m
    memory: 512Mi
  limits:
    cpu: 1000m
    memory: 1Gi

6Test health endpoint directly

Port-forward and test the readiness endpoint:

bash

kubectl port-forward pod/<pod-name> 8080:8080 -n <namespace> &
curl -v http://localhost:8080/health

If endpoint returns error or hangs, fix the application health check logic.

7Check Ingress controller buffer settings

Large responses may exceed proxy buffer size:

bash

kubectl describe ingress <ingress-name> -n <namespace>

For nginx-ingress, add annotation:

yaml

annotations:
  nginx.ingress.kubernetes.io/proxy-body-size: "50m"
  nginx.ingress.kubernetes.io/proxy-connect-timeout: "10"
  nginx.ingress.kubernetes.io/proxy-send-timeout: "30"
  nginx.ingress.kubernetes.io/proxy-read-timeout: "30"

How to fix 502 Bad Gateway in Kubernetes

What this error means

Typical symptoms

Common causes

How to fix "502 Bad Gateway"

Advanced notes

Related errors

Official resources & further reading