Переодически вылетает ошибка 502 - nginx

user nginx nobody;                  
worker_processes	16;               

error_log /var/log/nginx/error_log notice;

events {
##  worker_connections	2048;
  worker_connections	204800;
  use epoll;               
}

#worker_rlimit_nofile	32768;
worker_rlimit_nofile	327680;

http {
    include /etc/nginx/mime.types;
    default_type application/octet-stream;

upstream fpm-sock {
 server unix:/var/run/php5-fpm.sock;
 }

    log_format main
    '$remote_addr - $remote_user [$time_local] '
    '"$request" $status $bytes_sent '           
    '"$http_referer" "$http_user_agent" '       
    '"$gzip_ratio"';                            


#geoip_country	/usr/share/GeoIP/GeoIP.dat;
#geoip_city	/usr/share/GeoIP/GeoIPCity.dat;
#geoip_org	/usr/share/GeoIP/GeoIPISP.dat;

## Size Limits

keepalive_timeout 6000;

output_buffers 32 512k;
sendfile_max_chunk 128k;
postpone_output 1460;
server_names_hash_bucket_size 64;


client_max_body_size 100m;

## General Options
    ignore_invalid_headers	on;
    sendfile	on;
upload_progress uploads 1m;

## TCP options 
    tcp_nodelay	on;
    tcp_nopush	on;
    reset_timedout_connection on;

## Compression
    gzip		on;
    gzip_buffers	16 8k;
    gzip_comp_level	5;
    gzip_http_version	1.0;
    gzip_min_length	1000;
    gzip_types		text/plain text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript;
    gzip_vary		on;
    gzip_static		on;
    gzip_proxied	any;
    gzip_disable	msie6;

    index index.php index.html;

    include hosts/mysite.ru.conf;
...(здесь ещё 12 сайтов)
    include hosts/mysite-n.ru.conf;

}# end of http

    server {
	listen ***.**.**.**;
	server_name mysite.ru;
	#limit_conn one 60;
	access_log /var/log/nginx/mysite.access_log main;
	error_log /var/log/nginx/mysite.error_log info;  

	root /var/www/mysite.ru/htdocs;


	## www. redirect
	if ($host ~* ^(www\.)(.+)) {
	  set $rawdomain $2;
	  rewrite ^/(.*)$  http://$rawdomain/$1 permanent;
	}

	## rewrite rules for old site
	rewrite ^/art([0-9]*)\.html? /node/$1 permanent;
	rewrite ^/topic([0-9]*)\.html? /taxonomy/term/$1 permanent;
	rewrite ^/topic([0-9]*)-([0-9]*)\.html? /taxonomy/term/$1?page=$2 permanent;

	rewrite ^/reviews\.php /taxonomy/term/19 permanent;

	rewrite ^/theme([0-9]*)\.html? /old/theme.php?id=$1;
	rewrite ^/delivery_full_([0-9]*)\.html? /old/delivery.php?d=$1;
	rewrite ^/review([0-9]*)\.html? /old/review.php?id=$1;
	rewrite ^/show_review\.php /old/review.php;
	rewrite ^/archive\.php /archive/today permanent;

	rewrite ^/yandex.news/yandex.phtm /yandex.xml;

	rewrite ^/img/([^\.]*\.(jpg|gif)) /sites/default/files/img/$1 permanent;

	rewrite ^/info/(.*)\.htm /info/index.php?id=$1;
	rewrite ^/info/?$ /info/index.php;
	rewrite ^/info/sitemap.xml /info/sitemap.php;
	rewrite ^/egadget([1-9])\.xml /egadget/$1/feed permanent;

	if ($request_uri ~* "^/show_article\.php\?id=([0-9]*)") {
	  set $q $1;
	  set $args "";
	  rewrite ^\/.*$ /node/$q permanent;
	}

#        location ~* ^/(bank|nojob|pkuda|politi[ck]a|shkola)/? {
        location ~* ^/(nojob|pkuda|shkola)/? {
	proxy_pass   [url]http://old.mysite.ru;[/url]
	    proxy_redirect default;
	    proxy_set_header Host $host;
	    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }

        location ~* ^/(medi[ck])/? {
            proxy_pass   [url]http://med.mysite.ru;[/url]
            proxy_redirect default;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }


	## 6.x starts
	location / {
	  #rewrite ^/(.*)/$ /$1 permanent; # remove trailing slashes - disabled
	  try_files $uri @cache;
	}

	location @cache {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }

	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @drupal;

	  add_header Expires epoch;
	  add_header Cache-Control "must-revalidate, post-check=0, pre-check=0";
	  try_files /cache/normal/$host${uri}_$args.html @drupal;
	}

	location @drupal {
	  ###
	  ### now simplified to reduce rewrites
	  ###
	  rewrite ^/(.*)$  /index.php?q=$1 last;
	}

	location ~* (/\..*|settings\.php$|\.(htaccess|engine|inc|info|ini|install|module|profile|pl|po|pot|sh|.*sql|theme|tpl(\.php)?|xtmpl)$|^(Entries.*|Repository|Root|Tag|Template))$ {
	  deny all;
	}

	location ~* /files/.*\.php$ {
	  return 444;
	}
	location ~* /themes/.*\.php$ {
	  return 444;
	}

	location ~* \.php$ {
	  try_files $uri @drupal;       #check for existence of php file
	  fastcgi_pass		fpm-sock;
	  fastcgi_index		index.php;
	  fastcgi_param		SCRIPT_FILENAME /var/www/mysite.ru/htdocs$fastcgi_script_name;
	  include		fastcgi_params;
	}

	location ~ \.css$ {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }
	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @uncached;
	  access_log  off;
	  expires  max; #if using aggregator
	  try_files /cache/perm/$host${uri}_.css $uri =404;
	}
   
	location ~ \.js$ {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }
	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @uncached;
	  access_log  off;
	  expires  max; #if using aggregator
	  try_files /cache/perm/$host${uri}_.js $uri =404;
	}

	location ~ \.json$ {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }
	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @uncached;
	  access_log  off;
	  expires  max; #if using aggregator
	  try_files /cache/normal/$host${uri}_.json $uri =404;
	}

	location @uncached {
	  access_log  off;
	  expires  max; # max if using aggregator, otherwise sane expire time
	}

	location ~* /files/imagecache/ {
	  access_log         off;
	  try_files $uri @drupal;  #imagecache support - now it works
	}

	location ~* ^.+\.(jpg|jpeg|gif|png|ico)$ {
	  access_log      off;
	  expires         30d;
	  try_files $uri =404;
	}

	location ~* \.xml$ {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }
	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @drupal;
	  add_header Expires epoch;
	  add_header Cache-Control "must-revalidate, post-check=0, pre-check=0";
	  types { }
	  default_type application/rss+xml;
	  try_files /cache/normal/$host${uri}_.xml /cache/normal/$host${uri}_.html $uri @drupal;
	}

	location ~* /feed$ {
	  if ( $request_method !~ ^(GET|HEAD)$ ) {
	    return 405;
	  }
	  if ($http_cookie ~ "DRUPAL_UID") {
	    return 405;
	  }

	  error_page 405 = @drupal;
	  add_header Expires epoch;
	  add_header Cache-Control "must-revalidate, post-check=0, pre-check=0";
	  types { }
	  default_type application/rss+xml;
	  try_files /cache/normal/$host${uri}_.xml /cache/normal/$host${uri}_.html $uri @drupal;
	}



	location /rest/ {

		allow 127.0.0.1;
		allow ***.***.**.0/24;
		allow ***.**.***.**;
		deny  all;

		rewrite ^/(.*)$  /index.php?q=$1 break;

		include cors-nginx.conf;
		fastcgi_pass		fpm-sock;
		fastcgi_index		index.php;
		fastcgi_param		SCRIPT_FILENAME /var/www/mysite.ru/htdocs$fastcgi_script_name;
		include		fastcgi_params;

	}

    } # end of server

[27-Apr-2016 10:53:02.134969] NOTICE: pid 9079, fpm_event_loop(), line 367: ready to handle connections
[27-Apr-2016 10:53:03.135992] DEBUG: pid 9079, fpm_pctl_perform_idle_server_maintenance(), line 379: [pool www] currently 3 active children, 29 spare children, 32 running children. Spawning rate 1

[B]2016/04/26 12:01:21 [info] 17564#0: *60409567 recv() failed (104: Connection reset by peer) while sending to client, client: 52.90.204.194, server: mysite.ru, request: "GET ссылка HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock", host: "mysite.ru"[/B]
насколько я понимаю это и есть та ошибка, которая мне покоя не даёт
...
2016/04/26 12:01:25 [info] 17570#0: *60408601 client 195.93.246.156 closed keepalive connection (104: Connection reset by peer)
...
2016/04/26 12:01:27 [info] 17565#0: *60409629 client 164.132.161.86 closed keepalive connection
2016/04/26 12:01:27 [info] 17564#0: *60409573 client 31.13.144.8 closed keepalive connection (104: Connection reset by peer)
2016/04/26 12:01:27 [warn] 17565#0: *60409651 an upstream response is buffered to a temporary file /var/lib/nginx/tmp/fastcgi/3/57/0000981573 while reading upstream, client: 88.198.38.111, server: mysite.ru, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "mysite.ru"
2016/04/26 12:01:28 [info] 17565#0: *60409649 client 157.55.39.40 closed keepalive connection
...

;;;;;;;;;;;;;;;;;;;;;
; FPM Configuration ;
;;;;;;;;;;;;;;;;;;;;;

; All relative paths in this configuration file are relative to PHP's install
; prefix (/usr/lib/php5.3). This prefix can be dynamicaly changed by using the
; '-p' argument from the command line.

; Include one or more files. If glob(3) exists, it is used to include a bunch of
; files from a glob(3) pattern. This directive can be used everywhere in the
; file.
; Relative path can also be used. They will be prefixed by:
;  - the global prefix if it's been set (-p arguement)
;  - /usr/lib/php5.3 otherwise
;include=/etc/php/fpm-php5.3/fpm.d/*.conf

;;;;;;;;;;;;;;;;;;
; Global Options ;
;;;;;;;;;;;;;;;;;;

[global]
; Pid file
; Note: the default prefix is /var/lib
; Default Value: none
; Warning: pid file is overriden by the Gentoo init script.
; FPM will refuse to start if you uncomment this settingi and make use of the
; init script. 
; pid = /var/run/php-fpm.pid

; Error log file
; Note: the default prefix is /var/lib
; Default Value: log/php-fpm.log
error_log = /var/log/php-fpm.log

; Log level
; Possible Values: alert, error, warning, notice, debug
; Default Value: notice
log_level = debug

; If this number of child processes exit with SIGSEGV or SIGBUS within the time
; interval set by emergency_restart_interval then FPM will restart. A value
; of '0' means 'Off'.
; Default Value: 0
;emergency_restart_threshold = 0

; Interval of time used by emergency_restart_interval to determine when 
; a graceful restart will be initiated.  This can be useful to work around
; accidental corruptions in an accelerator's shared memory.
; Available Units: s(econds), m(inutes), h(ours), or d(ays)
; Default Unit: seconds
; Default Value: 0
;emergency_restart_interval = 1m

; Time limit for child processes to wait for a reaction on signals from master.
; Available units: s(econds), m(inutes), h(ours), or d(ays)
; Default Unit: seconds
; Default Value: 0
;process_control_timeout = 5s

; Send FPM to background. Set to 'no' to keep FPM in foreground for debugging.
; Default Value: yes
;daemonize = yes

;;;;;;;;;;;;;;;;;;;;
; Pool Definitions ; 
;;;;;;;;;;;;;;;;;;;;

; Multiple pools of child processes may be started with different listening
; ports and different management options.  The name of the pool will be
; used in logs and stats. There is no limitation on the number of pools which
; FPM can handle. Your system will tell you anyway :)

; Start a new pool named 'www'.
; the variable $pool can we used in any directive and will be replaced by the
; pool name ('www' here)
[www]

; Per pool prefix
; It only applies on the following directives:
; - 'slowlog'
; - 'listen' (unixsocket)
; - 'chroot'
; - 'chdir'
; - 'php_values'
; - 'php_admin_values'
; When not set, the global prefix (or /usr/lib/php5.3) applies instead.
; Note: This directive can also be relative to the global prefix.
; Default Value: none
;prefix = /path/to/pools/$pool

; The address on which to accept FastCGI requests.
; Valid syntaxes are:
;   'ip.add.re.ss:port'    - to listen on a TCP socket to a specific address on
;                            a specific port;
;   'port'                 - to listen on a TCP socket to all addresses on a
;                            specific port;
;   '/path/to/unix/socket' - to listen on a unix socket.
; Note: This value is mandatory.
;listen = 127.0.0.1:9000
listen = /var/run/php5-fpm.sock

; Set listen(2) backlog. A value of '-1' means unlimited.
; Default Value: 128 (-1 on FreeBSD and OpenBSD)
listen.backlog = 4096
 
; List of ipv4 addresses of FastCGI clients which are allowed to connect.
; Equivalent to the FCGI_WEB_SERVER_ADDRS environment variable in the original
; PHP FCGI (5.2.2+). Makes sense only with a tcp listening socket. Each address
; must be separated by a comma. If this value is left blank, connections will be
; accepted from any ip address.
; Default Value: any
;listen.allowed_clients = 127.0.0.1

; Set permissions for unix socket, if one is used. In Linux, read/write
; permissions must be set in order to allow connections from a web server. Many
; BSD-derived systems allow connections regardless of permissions. 
; Default Values: user and group are set as the running user
;                 mode is set to 0666
listen.owner = nobody
listen.group = nobody
listen.mode = 0666

; Unix user/group of processes
; Note: The user is mandatory. If the group is not set, the default user's group
;       will be used.
user = nobody
group = nobody

; Choose how the process manager will control the number of child processes.
; Possible Values:
;   static  - a fixed number (pm.max_children) of child processes;
;   dynamic - the number of child processes are set dynamically based on the
;             following directives:
;             pm.max_children      - the maximum number of children that can
;                                    be alive at the same time.
;             pm.start_servers     - the number of children created on startup.
;             pm.min_spare_servers - the minimum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is less than this
;                                    number then some children will be created.
;             pm.max_spare_servers - the maximum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is greater than this
;                                    number then some children will be killed.
; Note: This value is mandatory.
;pm = static
pm = dynamic

; The number of child processes to be created when pm is set to 'static' and the
; maximum number of child processes to be created when pm is set to 'dynamic'.
; This value sets the limit on the number of simultaneous requests that will be
; served. Equivalent to the ApacheMaxClients directive with mpm_prefork.
; Equivalent to the PHP_FCGI_CHILDREN environment variable in the original PHP
; CGI.
; Note: Used when pm is set to either 'static' or 'dynamic'
; Note: This value is mandatory.
;pm.max_children = 16
pm.max_children = 128

; The number of child processes created on startup.
; Note: Used only when pm is set to 'dynamic'
; Default Value: min_spare_servers + (max_spare_servers - min_spare_servers) / 2
pm.start_servers = 32

; The desired minimum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.min_spare_servers = 8

; The desired maximum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.max_spare_servers = 32
 
; The number of requests each child process should execute before respawning.
; This can be useful to work around memory leaks in 3rd party libraries. For
; endless request processing specify '0'. Equivalent to PHP_FCGI_MAX_REQUESTS.
; Default Value: 0
pm.max_requests = 500

; The URI to view the FPM status page. If this value is not set, no URI will be
; recognized as a status page. By default, the status page shows the following
; information:
;   accepted conn        - the number of request accepted by the pool;
;   pool                 - the name of the pool;
;   process manager      - static or dynamic;
;   idle processes       - the number of idle processes;
;   active processes     - the number of active processes;
;   total processes      - the number of idle + active processes.
;   max children reached - number of times, the process limit has been reached,
;                          when pm tries to start more children (works only for
;                          pm 'dynamic')
; The values of 'idle processes', 'active processes' and 'total processes' are
; updated each second. The value of 'accepted conn' is updated in real time.
; Example output:
;   accepted conn:        12073
;   pool:                 www
;   process manager:      static
;   idle processes:       35
;   active processes:     65
;   total processes:      100
;   max children reached: 1
; By default the status page output is formatted as text/plain. Passing either
; 'html' or 'json' as a query string will return the corresponding output
; syntax. Example:
;   http://www.foo.bar/status
;   http://www.foo.bar/status?json
;   http://www.foo.bar/status?html
; Note: The value must start with a leading slash (/). The value can be
;       anything, but it may not be a good idea to use the .php extension or it
;       may conflict with a real PHP file.
; Default Value: not set 
pm.status_path = /statusphpfpmbysergeyfortest.php
 
; The ping URI to call the monitoring page of FPM. If this value is not set, no
; URI will be recognized as a ping page. This could be used to test from outside
; that FPM is alive and responding, or to
; - create a graph of FPM availability (rrd or such);
; - remove a server from a group if it is not responding (load balancing);
; - trigger alerts for the operating team (24/7).
; Note: The value must start with a leading slash (/). The value can be
;       anything, but it may not be a good idea to use the .php extension or it
;       may conflict with a real PHP file.
; Default Value: not set
;ping.path = /ping
ping.path = /pingphpfpmbysergeyfortest.php

; This directive may be used to customize the response of a ping request. The
; response is formatted as text/plain with a 200 response code.
; Default Value: pong
;ping.response = pong
 
; The timeout for serving a single request after which the worker process will
; be killed. This option should be used when the 'max_execution_time' ini option
; does not stop script execution for some reason. A value of '0' means 'off'.
; Available units: s(econds)(default), m(inutes), h(ours), or d(ays)
; Default Value: 0
;request_terminate_timeout = 0
 
; The timeout for serving a single request after which a PHP backtrace will be
; dumped to the 'slowlog' file. A value of '0s' means 'off'.
; Available units: s(econds)(default), m(inutes), h(ours), or d(ays)
; Default Value: 0
;request_slowlog_timeout = 0
 
; The log file for slow requests
; Default Value: not set
; Note: slowlog is mandatory if request_slowlog_timeout is set
;slowlog = /var/log/php-fpm-$pool.log.slow
 
; Set open file descriptor rlimit.
; Default Value: system defined value
rlimit_files = 65535
 
; Set max core size rlimit.
; Possible Values: 'unlimited' or an integer greater or equal to 0
; Default Value: system defined value
;rlimit_core = 0
 
; Chroot to this directory at the start. This value must be defined as an
; absolute path. When this value is not set, chroot is not used.
; Note: you can prefix with '$prefix' to chroot to the pool prefix or one
; of its subdirectories. If the pool prefix is not set, the global prefix
; will be used instead.
; Note: chrooting is a great security feature and should be used whenever 
;       possible. However, all PHP paths will be relative to the chroot
;       (error_log, sessions.save_path, ...).
; Default Value: not set
;chroot = 
 
; Chdir to this directory at the start.
; Note: relative path can be used.
; Default Value: current directory or / when chroot
;chdir = /var/www
 
; Redirect worker stdout and stderr into main error log. If not set, stdout and
; stderr will be redirected to /dev/null according to FastCGI specs.
; Note: on highloaded environement, this can cause some delay in the page
; process time (several ms).
; Default Value: no
catch_workers_output = yes
 
; Pass environment variables like LD_LIBRARY_PATH. All $VARIABLEs are taken from
; the current environment.
; Default Value: clean env
;env[HOSTNAME] = $HOSTNAME
;env[PATH] = /usr/local/bin:/usr/bin:/bin
;env[TMP] = /tmp
;env[TMPDIR] = /tmp
;env[TEMP] = /tmp

; Additional php.ini defines, specific to this pool of workers. These settings
; overwrite the values previously defined in the php.ini. The directives are the
; same as the PHP SAPI:
;   php_value/php_flag             - you can set classic ini defines which can
;                                    be overwritten from PHP call 'ini_set'. 
;   php_admin_value/php_admin_flag - these directives won't be overwritten by
;                                     PHP call 'ini_set'
; For php_*flag, valid values are on, off, 1, 0, true, false, yes or no.

; Defining 'extension' will load the corresponding shared extension from
; extension_dir. Defining 'disable_functions' or 'disable_classes' will not
; overwrite previously defined php.ini values, but will append the new value
; instead.

; Note: path INI options can be relative and will be expanded with the prefix
; (pool, global or /usr/lib/php5.3)

; Default Value: nothing is defined by default except the values in php.ini and
;                specified at startup with the -d argument
;php_admin_value[sendmail_path] = /usr/sbin/sendmail -t -i -f www@my.domain.com
;php_flag[display_errors] = on
;php_admin_value[error_log] = /var/log/fpm-php.www.log
;php_admin_flag[log_errors] = on
;php_admin_value[memory_limit] = 32M

[27-Apr-2016 10:53:02.134969] NOTICE: pid 9079, fpm_event_loop(), line 367: ready to handle connections
[27-Apr-2016 10:53:03.135992] DEBUG: pid 9079, fpm_pctl_perform_idle_server_maintenance(), line 379: [pool www] currently 3 active children, 29 spare children, 32 running children. Spawning rate 1

NOTICE: pid 27839, fmp_pctl_exit(), line 70: exiting, bye-bye! - что это, не пойму.