Sometimes Apache hangs (FastCGI + APC)

I’m trying to tuning a VPS with WHM for a single website.
Sometimes, specially when I have more than 50 users connected, Apache hangs: I get a lot of "W" Sending Reply status from WHM » Home » Server Status » Apache Status and after some minutes the site get to work again.
During this problematic status CPU are not loaded and memory isn’t full.
I’ve captured Apache status and mysqlmymonlite report during the problematic minutes (attached) and here some relevant settings:

Code:

 /usr/local/lib/php.ini
[APC]
apc.enabled = 1
apc.shm_segments = 1
apc.shm_size = 512M
apc.num_files_hint = 10000
apc.stat = 0

 /usr/local/apache/conf/includes/post_virtualhost_global.conf
<IfModule mod_fcgid.c>
MaxRequestsPerProcess 2000
FcgidMaxProcesses 80
FcgidProcessLifeTime 240
MaxProcessCount 100
FcgidIOTimeout 240
FcgidIdleTimeout 60
FcgidIdleScanInterval 90
FcgidBusyTimeout 300
FcgidBusyScanInterval 80
ErrorScanInterval 3
ZombieScanInterval 3
DefaultMinClassProcessCount 0
DefaultMaxClassProcessCount 6
FcgidMaxRequestLen 1073741824
</IfModule>

/etc/my.cnf
[mysqld]
innodb_file_per_table=1
max_allowed_packet=268435456
key_buffer_size=64M
query_cache_type=1
query_cache_size=96M
query_cache_limit=2M
sort_buffer_size=8M
table_cache=4092
innodb_buffer_pool_size=356M
innodb_flush_log_at_trx_commit=2
innodb_thread_concurrency=2
thread_cache_size=4
join_buffer_size=2M
tmp_table_size=32M
max_heap_table_size=32M
max_connections=100

Can you help me to understand why it happens?

 

Thanks for your answer Michael, nothing of interest at my eyes.

 

Thanks for the suggestion: I’ve found only warnings related to FCGI in /usr/local/apache/logs/error_log for the "hang time slot"

Code:

[Tue Aug 26 19:15:49.612361 2014] [fcgid:warn] [pid 19097] [client 212.124.191.107:54951] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:15:50.153824 2014] [fcgid:warn] [pid 19113] [client 93.38.113.130:32936] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/fraternita/cellole/lavoro-a-cellole
[Tue Aug 26 19:15:50.720636 2014] [fcgid:warn] [pid 19072] [client 178.154.243.74:43685] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:15:53.182748 2014] [fcgid:warn] [pid 19055] [client 37.58.100.181:34372] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:15:55.391538 2014] [fcgid:warn] [pid 19134] [client 82.187.216.230:2056] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: https://WWW.MASKEDHOST.EXT/lavoro/acquista/olio
[Tue Aug 26 19:15:57.493557 2014] [fcgid:warn] [pid 19135] [client 79.16.172.243:51148] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/fraternita/cellole/la-pieve-cellole/la-chiesa-cellole
[Tue Aug 26 19:15:58.035601 2014] [fcgid:warn] [pid 19136] [client 87.25.5.10:64315] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:15:59.163578 2014] [fcgid:warn] [pid 19124] [client 93.38.113.130:32937] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/fraternita/cellole/lavoro-a-cellole
[Tue Aug 26 19:15:59.783090 2014] [fcgid:warn] [pid 19087] [client 82.187.216.230:3506] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: https://WWW.MASKEDHOST.EXT/lavoro/acquista/olio
[Tue Aug 26 19:16:00.325320 2014] [fcgid:warn] [pid 19133] [client 79.41.104.155:49561] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/priore/articoli?start=230
[Tue Aug 26 19:16:01.212326 2014] [fcgid:warn] [pid 19139] [client 95.233.60.117:57486] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/priore/articoli
[Tue Aug 26 19:16:01.213094 2014] [fcgid:warn] [pid 19138] [client 72.77.175.243:50921] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/en/prayer/lectio-divina/1751-pray?start=2
[Tue Aug 26 19:16:01.271933 2014] [fcgid:warn] [pid 19061] [client 2.192.26.52:50028] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/preghiera/per-pregare-con-noi/lezionario
[Tue Aug 26 19:16:03.686871 2014] [fcgid:warn] [pid 19032] [client 123.125.71.96:60578] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:16:04.548563 2014] [fcgid:warn] [pid 19100] [client 188.63.238.36:53769] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:16:04.595250 2014] [fcgid:warn] [pid 19137] [client 93.38.113.130:32939] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5
[Tue Aug 26 19:16:05.142426 2014] [fcgid:warn] [pid 19041] [client 82.187.216.230:3277] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: https://WWW.MASKEDHOST.EXT/lavoro/acquista/olio
[Tue Aug 26 19:16:06.009796 2014] [fcgid:warn] [pid 19140] [client 151.49.56.70:49432] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://duomosandona.netsons.org/
[Tue Aug 26 19:16:06.795535 2014] [fcgid:warn] [pid 19141] [client 79.22.46.210:24000] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/preghiera/vangelo
[Tue Aug 26 19:16:07.197494 2014] [fcgid:warn] [pid 19142] [client 2.192.26.52:50033] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5, referer: http://WWW.MASKEDHOST.EXT/
[Tue Aug 26 19:16:07.320954 2014] [fcgid:warn] [pid 19101] [client 79.26.168.203:51273] mod_fcgid: can't apply process slot for /usr/local/cpanel/cgi-sys/php5