FPM health check

Description

The idea is to have a native support for the functionality offered by https://github.com/renatomefi/php-fpm-healthcheck . It means having endpoint that will return selected response (defaulting to 200 without body) if selected metrics in scoreboard are above specified threshold. Those metrics would be configurable in FPM config together with endpoint (listen and path like for status) and the actual response.

The main use case for this functionality are Kubernetes probes and possibly some monitoring tools. It should be more convenient for users and also require less resources then doing periodic status checks which need to collect all metrics.

首先查看 issue 中描述的 PHP-FPM 状态端点、scoreboard 指标和 FPM 配置，然后比较 php-fpm-healthcheck 的行为。当可配置的 health 端点能够选择 scoreboard 阈值、监听和路径设置以及其响应，同时支持 Kubernetes 探针和监控使用场景时，即视为完成。