# upstream sent HTTP/1.0 response while reading response header from upstream, client: 192.168.1.10

- **ID:** `nginx/upstream-sent-http-1-0`
- **Domain:** nginx
- **Category:** protocol_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Upstream server sent an HTTP/1.0 response when nginx expected HTTP/1.1 or higher, often due to a misconfigured backend or legacy application.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| nginx 1.18.0 | active | — | — |
| nginx 1.20.2 | active | — | — |
| nginx 1.24.0 | active | — | — |

## Workarounds

1. **Configure upstream to use HTTP/1.1 (e.g., for Node.js: set 'keepAliveTimeout' and HTTP version; for Apache: ensure 'SetEnv nokeepalive 0' is not set).** (85% success)
   ```
   Configure upstream to use HTTP/1.1 (e.g., for Node.js: set 'keepAliveTimeout' and HTTP version; for Apache: ensure 'SetEnv nokeepalive 0' is not set).
   ```
2. **In nginx, set proxy_http_version to 1.1 and ensure proxy_set_header Connection ''; to handle keep-alive properly:
proxy_http_version 1.1;
proxy_set_header Connection '';** (75% success)
   ```
   In nginx, set proxy_http_version to 1.1 and ensure proxy_set_header Connection ''; to handle keep-alive properly:
proxy_http_version 1.1;
proxy_set_header Connection '';
   ```
3. **If upstream is a legacy system that only supports HTTP/1.0, consider using a middleware proxy that upgrades the protocol.** (40% success)
   ```
   If upstream is a legacy system that only supports HTTP/1.0, consider using a middleware proxy that upgrades the protocol.
   ```

## Dead Ends

- **** — This forces nginx to speak HTTP/1.0 to upstream, but may cause other issues like missing chunked transfer encoding; the error remains if upstream still sends HTTP/1.0. (60% fail)
- **** — Buffering does not change the protocol version; the error will still appear in logs and may cause intermittent failures. (75% fail)
- **** — Restarting does not change the protocol version the upstream uses; misconfiguration persists. (85% fail)