zitadel/apps/docs/content/self-hosting/deploy/troubleshooting/_upstream_header.mdx

If you operate Zitadel behind a Reverse Proxy or Ingress inside a Kubernetes cluster,
you may encounter an Error like `upstream sent too big header while reading response header from upstream`
in your NGINX Logs and receive a 403 Error when accessing NGINX.

you can solve it by increasing the grpc buffer size in your nginx config:

### Ingress NGINX
```yaml
ingress:
enabled: true
annotations:
    nginx.ingress.kubernetes.io/modsecurity-snippet: |
        SecRuleRemoveById 949110
    nginx.ingress.kubernetes.io/backend-protocol: "GRPC"
    nginx.ingress.kubernetes.io/configuration-snippet: |
        grpc_set_header Host $host;
        more_clear_input_headers "Host" "X-Forwarded-Host";
        proxy_set_header Host $http_host;
        proxy_set_header X-Forwarded-Host $http_x_forwarded_host;
    # highlight-next-line
    nginx.ingress.kubernetes.io/server-snippet: "grpc_buffer_size 8k;"
```
### NGINX Config
```nginx
    http {
        server {
            listen 80;
            http2 on;
            location / {
                grpc_pass grpc://zitadel-disabled-tls:8080;
                grpc_set_header Host $host:$server_port;
                # highlight-next-line
                grpc_buffer_size 8k;
            }
        }
    }
```