A Nginx module which can keep backends' response time in a specified header
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README.md
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ngx_http_spent_filter_module.c

README.md

nginx-http-spent-filter-module

Introduction

This module is part of a company project which aims to locate the bottlenecks of backend servers from the client-side point of view. It records a request's start-time and finish-time into the header set by spent_header, by the mean time, keeping every en route phase's in it.

Sample

  • Configuration

      location /static/js/ {
          spent passive;
          spent_header X-Spent;
          spent_header p;
      }
    
  • Part of response headers seen by client (timestamp prefix by d is generated by some other backend server (another Nignx instance, php-fpm etc.)).

      ...
      Content-Type: text/plain\r\n
      X-Spent: p100.123;d100.124;d100.125;p100.126\r\n
      ...
    

Available Directives

syntax: spent passive | active | off
default: spent off
context: http, server, location

It enables the module working in different mode, or just disable it completely in a given context.

  • off turns the module off;
  • passive means the operation is triggered by header from upstream;
  • active makes header specified by spent_header added whatsoever;

syntax: spent_header customized_header
default: spent_header X-Spent
context: http, server, location

It specifies which header to operate on.

syntax: spent_prefix identifier
default: spent_prefix p
context: http, server, location

It specifies prefix of timestamp generate by current Nginx instance.

Notes

  • Avoid using standard headers or Nginx pre-defined headers. Nginx may hide them from downstream.

  • Nginx timestamps returned by ngx_timeofday are not produced in real-time by syscall s. They are from a cache, actually. So you may observe finish-time equals to start-time quite often if your request is processed very quickly.