Hi everyone,

I have a php-fpm backend. And sometimes I got nginx return 502. After I check the error_log I found each 502s are caused by upstream sent invalid status "0" while reading response header from upstream

The error_log are in the form "upstream sent invalid status "0" while reading response header from upstream client: 127.0.0.1, server: xxxx, request: "xxxxx HTTP/1.0", upstream: "fastcgi://unix:/dev/shm/api-php.socket:", host: "xxxx", referrer: "xxxx""

Does anyone have same experience? I have no idea after search Google 'upstream sent invalid status "0"'

I think it is caused by PHP. But why does it sent status '0'?

Yours Sincerely.