How to troubleshoot 500 and 502 errors in the php+nginx service

概述

当线上的服务中访问中出现500或者502错误时，需要紧急处理，排查问题，该怎么做？可以通过分析一些错误日志或者跟踪php-fpm进程来进行问题定位。

nginx error_log

nginx的error_log在nginx的配置文件中定义的

server {
 listen  80;
 server_name localhost;
 root   /var/www;

 access_log /users/jiao/logs/default.access.log;
 error_log /users/jiao/logs/default.error.log;
 location / {
  index index.html index.htm index.php;
  autoindex on;
 }
 location = /info {
  allow 127.0.0.1;
  deny all;
  rewrite (.*) /.info.php;
 }
 location ~ \.php$ {
  root /var/www;
  fastcgi_pass 127.0.0.1:9000;
  fastcgi_index index.php;
  fastcgi_param script_filename /var/www$fastcgi_script_name;
  include /usr/local/etc/nginx/fastcgi_params;
 }
}

查看error_log

➜  tail /users/jiao/logs/default.error.log
2019/07/17 11:08:18 [error] 77416#0: *76 kevent() reported about an closed connection (54: connection reset by peer) while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "get / http/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "localhost"

发现出现了connection reset by peer，连接被重置了，此时可以再查看php-fpm的error_log进一步分析问题

php-fpm error_log

php-fpm的error_log在php-fpm.conf文件中配置中定义的

; error log file
; if it's set to "syslog", log is sent to syslogd instead of being written
; in a local file.
; note: the default prefix is /usr/local/var
; default value: log/php-fpm.log
error_log = log/php-fpm.log

error_log里面的内容是这样的

➜ tail /usr/local/var/log/php-fpm.log
[17-jul-2019 10:49:54] notice: [pool www] child 81948 started
[17-jul-2019 11:08:18] warning: [pool www] child 77537, script '/var/www/index.php' (request: "get /index.php") execution timed out (3.801267 sec), terminating
[17-jul-2019 11:08:18] warning: [pool www] child 77537 exited on signal 15 (sigterm) after 1503.113967 seconds from start
[17-jul-2019 11:08:18] notice: [pool www] child 94339 started

可以看到是请求/var/www/index.php文件出现了超时

dtruss

dtruss是动态跟踪命令，可以根据pid，name跟踪进程

mac环境下使用dtruss，linux环境可以使用strace，pstack

➜ dtruss 
usage: dtruss [-acdefholls] [-t syscall] { -p pid | -n name | command | -w name }

  -p pid   # examine this pid
  -n name   # examine this process name
  -t syscall  # examine this syscall only
  -w name   # wait for a process matching this name
  -a    # print all details
  -c    # print syscall counts
  -d    # print relative times (us)
  -e    # print elapsed times (us)
  -f    # follow children
  -l    # force printing pid/lwpid
  -o    # print on cpu times
  -s    # print stack backtraces
  -l    # don't print pid/lwpid
  -b bufsize  # dynamic variable buf size

eg,

 dtruss df -h  # run and examine "df -h"
 dtruss -p 1871  # examine pid 1871
 dtruss -n tar  # examine all processes called "tar"
 dtruss -f test.sh # run test.sh and follow children

跟踪php-fpm：sudo dtruss -a -n php-fpm<br>

此时访问web页面，就可以看到跟踪内容

21416/0x3479b6:  1559  63  3 getrusage(0x0, 0x7ffee1ec0760, 0x0)   = 0 0
21416/0x3479b6:  1561  4  0 getrusage(0xffffffffffffffff, 0x7ffee1ec0760, 0x0)   = 0 0
21416/0x3479b6:  1627  77  17 poll(0x7ffee1ec08c0, 0x1, 0x1388)   = 1 0
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
21416/0x3479b6:  1872  29  24 lstat64("/var/www/index.php\0", 0x7ffee1ecff38, 0x0)   = 0 0
21416/0x3479b6:  1884  9  6 lstat64("/var/www\0", 0x7ffee1ecfdf8, 0x0)   = 0 0
21416/0x3479b6:  1889  6  3 lstat64("/var\0", 0x7ffee1ecfcb8, 0x0)   = 0 0
21416/0x3479b6:  1899  12  8 readlink("/var\0", 0x7ffee1ed0090, 0x400)   = 11 0
21416/0x3479b6:  1905  6  4 lstat64("/private/var\0", 0x7ffee1ecfb78, 0x0)   = 0 0
21416/0x3479b6:  1917  6  3 lstat64("/private\0", 0x7ffee1ecfa38, 0x0)   = 0 0
21416/0x3479b6:  2178  18  14 stat64("/var/www/.user.ini\0", 0x7ffee1ed0240, 0x0)   = -1 err#2
21416/0x3479b6:  2217  5  1 setitimer(0x2, 0x7ffee1ed07e0, 0x0)   = 0 0
21416/0x3479b6:  2225  4  0 sigaction(0x1b, 0x7ffee1ed0788, 0x7ffee1ed07b0)   = 0 0
21416/0x3479b6:  2237  5  1 sigprocmask(0x2, 0x7ffee1ed0804, 0x0)   = 0x0 0
21416/0x3479b6:  3643  48  40 open_nocancel(".\0", 0x0, 0x1)   = 5 0
21416/0x3479b6:  3648  7  3 fstat64(0x5, 0x7ffee1ed0110, 0x0)   = 0 0
21416/0x3479b6:  3653  7  2 fcntl_nocancel(0x5, 0x32, 0x10f252158)   = 0 0
21416/0x3479b6:  3661  12  7 close_nocancel(0x5)   = 0 0
21416/0x3479b6:  3670  10  7 stat64("/usr/local/var\0", 0x7ffee1ed0080, 0x0)   = 0 0
21416/0x3479b6:  3681  11  8 chdir("/var/www\0", 0x0, 0x0)   = 0 0
21416/0x3479b6:  3698  4  0 setitimer(0x2, 0x7ffee1ed02d0, 0x0)   = 0 0
21416/0x3479b6:  3710  6  3 fcntl(0x3, 0x8, 0x10f3fd858)   = 0 0
21416/0x3479b6:  3733  9  6 stat64("/private/var/www/index.php\0", 0x7ffee1ecff10, 0x0)   = 0 0
74904/0x332630: 723125 1073381  19 kevent(0x9, 0x0, 0x0)   = 0 0
74902/0x332629: 770666 1073387  17 kevent(0x8, 0x0, 0x0)   = 0 0
74904/0x332630: 723165 1061954  20 kevent(0x9, 0x0, 0x0)   = 0 0
74902/0x332629: 770709 1061954  20 kevent(0x8, 0x0, 0x0)   = 0 0
74904/0x332630: 723201 1074786  16 kevent(0x9, 0x0, 0x0)   = 0 0
74902/0x332629: 770747 1074783  16 kevent(0x8, 0x0, 0x0)   = 0 0
74904/0x332630: 723229 1069141  13 kevent(0x9, 0x0, 0x0)   = 0 0
74902/0x332629: 770777 1069145  11 kevent(0x8, 0x0, 0x0)   = 0 0
21416/0x3479b6:  3942 3902233  7 __semwait_signal(0x703, 0x0, 0x1)   = -1 err#4
74902/0x332629: 770814  103  25 kill(21416, 15)   = 0 0
dtrace: error on enabled probe id 2172 (id 161: syscall::write:return): invalid kernel access in action #13 at dif offset 68
dtrace: error on enabled probe id 2172 (id 161: syscall::write:return): invalid kernel access in action #13 at dif offset 68
74902/0x332629: 771325  7  2 sigreturn(0x7ffee1ecfc40, 0x1e, 0xc1a4b78e0404663a)   = 0 err#-2
74902/0x332629: 771336  7  3 kevent(0x8, 0x0, 0x0)   = 1 0
dtrace: error on enabled probe id 2174 (id 159: syscall::read:return): invalid kernel access in action #13 at dif offset 68
74902/0x332629: 771352  11  7 wait4(0xffffffffffffffff, 0x7ffee1ed0748, 0x3)   = 21416 0
dtrace: error on enabled probe id 2172 (id 161: syscall::write:return): invalid kernel access in action #13 at dif offset 68
74902/0x332629: 773511 1957 1899 fork()   = 28060 0
28060/0x3754c5:  125:  0:  0 fork()   = 0 0
28060/0x3754c5:  128  9  2 bsdthread_register(0x7fff6774c418, 0x7fff6774c408, 0x2000)   = -1 err#22
dtrace: error on enabled probe id 2172 (id 161: syscall::write:return): invalid kernel access in action #13 at dif offset 68
74902/0x332629: 773737  4  1 wait4(0xffffffffffffffff, 0x7ffee1ed0748, 0x3)   = 0 0
74902/0x332629: 773742  6  3 read(0x5, "\0", 0x1)   = -1 err#35
28060/0x3754c5:  320  4  0 getpid(0x0, 0x0, 0x0)   = 28060 0
28060/0x3754c5:  328  7  2 __mac_syscall(0x7fff67758a17, 0x4, 0x7ffee1ed0208)   = -1 err#45
28060/0x3754c5:  332  5  2 csops(0x6d9c, 0xb, 0x7ffee1ed0248)   = -1 err#22
28060/0x3754c5:  755  14  11 dup2(0x1, 0x2, 0x0)   = 2 0
28060/0x3754c5:  797  89  22 close(0x4)   = 0 0
28060/0x3754c5:  806  11  6 dup2(0x7, 0x0, 0x0)   = 0 0
28060/0x3754c5:  817  4  0 geteuid(0x0, 0x0, 0x0)   = 501 0
28060/0x3754c5:  820  3  0 close(0x5)   = 0 0
28060/0x3754c5:  821  3  0 close(0x6)   = 0 0
28060/0x3754c5:  824  5  1 sigaction(0xf, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  825  3  0 sigaction(0x2, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  827  3  0 sigaction(0x1e, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  828  3  0 sigaction(0x1f, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  829  3  0 sigaction(0x14, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  830  3  0 sigaction(0x3, 0x7ffee1ed0688, 0x0)   = 0 0
28060/0x3754c5:  1043  3  0 close(0x7)   = 0 0

可以看到系统底层执行的函数，如lstat64获取文件内容信息，kill(21416, 15)kill掉php-fpm进程，fork()出新的php-fpm进程

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