Otdfbt

I have a varnish 4 in front of an Apache web server.
All is good, except i have some random 502 errors.

What is strange is that there is nothing in the varnishlog file for this error ! (all others requests are logged)

My parameters :
VARNISH_MIN_THREADS=50
VARNISH_MAX_THREADS=1000
VARNISH_THREAD_TIMEOUT=120

What i can do in order to fix this ?

My default.vcl :

vcl 4.0;

backend default 
 .host = "127.0.0.1";
 .port = "8055";


backend php53 
 .host = "127.0.0.1";
 .port = "8053";


sub vcl_recv 
 req.http.Host ~ "site2")
 
 set req.backend_hint = php53;
 

 if (req.http.Host ~ "mainsite" )
 if (req.method == "POST") 
 return (pipe);
 
 if (req.method == "GET" && (req.url ~ "^/admin")) 
 return (pass);
 
 

 if (req.method != "GET" && req.method != "HEAD")
 
 return (pass);
 

 if (req.url ~ "(?i).(jpeg
sub vcl_backend_response 
 if (beresp.http.Content-Length !~ "[0-9]7,10") 
 return(deliver);
 

i have 502 errors on 'mainsite' (prestashop ecommerce, with lot of images)

My current stat :

MAIN.uptime 151353 1.00 Child process uptime
MAIN.sess_conn 59309 0.39 Sessions accepted

MAIN.sess_drop 0 0.00 Sessions dropped

MAIN.sess_fail 0 0.00 Session accept failures

MAIN.backend_conn 24076 0.16 Backend conn. success

MAIN.backend_unhealthy 0 0.00 Backend conn. not attempted

MAIN.backend_busy 0 0.00 Backend conn. too many

MAIN.backend_fail 85 0.00 Backend conn. failures

MAIN.backend_reuse 53606 0.35 Backend conn. reuses

MAIN.backend_toolate 11249 0.07 Backend conn. was closed

MAIN.backend_recycle 64856 0.43 Backend conn. recycles

MAIN.backend_retry 0 0.00 Backend conn. retry

MAIN.threads 100 . Total number of threads

MAIN.threads_created 108 0.00 Threads created

MAIN.threads_destroyed 8 0.00 Threads destoryed

MAIN.threads_failed 0 0.00 Thread creation failed

MAIN.busy_sleep 3 0.00 Number of requests sent to sleep on busy
objhdr

MAIN.busy_wakeup 3 0.00 Number of requests woken after sleep on busy objhdr

MAIN.sess_queued 11 0.00 Sessions queued for thread

ps aux | grep -i varnish | grep -v grep :

root 22319 0.0 0.5 121896 84060 ? SLs 12:21 0:00 /usr/sbin/varnishd -P /var/run/varnish.pid -a :80 -f /etc/varnish/default.vcl -T 127.0.0.1:6082 -t 120 -p thread_pool_min=50 -p thread_pool_max=1000 -p thread_pool_timeout=120 -u varnish -g varnish -S /etc/varnish/secret -s malloc,1G
varnish 22321 0.4 0.5 321348 92604 ? Sl 12:21 0:00 /usr/sbin/varnishd -P /var/run/varnish.pid -a :80 -f /etc/varnish/default.vcl -T 127.0.0.1:6082 -t 120 -p thread_pool_min=50 -p thread_pool_max=1000 -p thread_pool_timeout=120 -u varnish -g varnish -S /etc/varnish/secret -s malloc,1G

have you looked into apache error log for "mainsite" ?

paste output of :

ps aux | grep -i varnish | grep -v grep

And see if your malloc size is not big to serve big contents size

Try: beresp.http.Content-Length !~ "keep this size small" (if that is the case)
Note: change that to regex to meet ur requirement where it says keep this size small

and check if you still get that error,