# rpc error: code = Unimplemented desc = unexpected HTTP status code received from server: 404 (Not Found); transport: received unexpected content-type "text/plain"

- **ID:** `go/grpc-code-unimplemented-proto-drift`
- **Domain:** go
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The client reached an HTTP server that is not a gRPC server (e.g., a plain HTTP reverse proxy, a misconfigured ingress, or an Envoy route not configured for gRPC). The server returned a text/plain 404 instead of gRPC frames.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.0+ | active | — | — |

## Workarounds

1. **** (90% success)
   ```
   // Kubernetes ingress-nginx:
// annotations:
//   nginx.ingress.kubernetes.io/backend-protocol: "GRPC"
//   nginx.ingress.kubernetes.io/ssl-redirect: "true"
   ```
2. **** (92% success)
   ```
   // Use the gRPC service port (often 50051) rather than 8080/9090
conn, _ := grpc.Dial("svc:50051", grpc.WithTransportCredentials(insecure.NewCredentials()))
   ```

## Dead Ends

- **** — The routing is misconfigured; retries always hit the same HTTP endpoint (95% fail)
- **** — The problem is HTTP/gRPC protocol mismatch, not TLS (90% fail)