Apache doesnt appear to be using multiple cores

apache-2.2httpmulti-core

I have a dedicated server with 16gb RAM with a Xeon E5504(8cores @2.0GHZ) running with Centos 7. I ran the top command and can see that 7 of the cores are close to idle most of the time and then one single cores is going flat out. Ive see it go above 100% which i dont understand.

%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem : 16479600 total,  1233968 free,   616824 used, 14628808 buff/cache
KiB Swap:   523260 total,   499720 free,    23540 used. 15342640 avail Mem

The server is used only as a web host. Apache, MySQL and PHP. I havnt made any changes to apache from its default config. I have heard that the default apache config supports multiple threads, but this clearly isnt the case.

mysqld and httpd are the only things using large amounts of resources. In total apache gets around 100k requests per week. More than enough for this server, but as i continue to add more sites, i dont want to slow it down since everything is on the same CPU.

I read into it an it seems that "prefork" needs to be modified in order to make apache take more resources. I ran the following command to see the default config and it doesnt look like prefork is even installed

/usr/sbin/apachectl -l
Compiled in modules:
  core.c
  mod_so.c
  http_core.c

Im not sure how to test the system to know what the current config is and why only one core is being used. I didnt notice much of a performance increase when moving sites from a low end single core VPS to this server, so im worried something is wrong with the config.

I checked /etc/http/conf/httpd.conf and all thats here are the virtual hosts. There are no lines related to the max clients and other values ive seen people using in the prefork if statement.

Best Answer

Top tells your your system isn't doing anything, as it is 100% idle.

The fields have the following meaning and don't specify specific cores.

       us, user    : time running un-niced user processes
       sy, system  : time running kernel processes
       ni, nice    : time running niced user processes
       wa, IO-wait : time waiting for I/O completion
       hi : time spent servicing hardware interrupts
       si : time spent servicing software interrupts
       st : time stolen from this vm by the hypervisor

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Hmm, I am pretty suspicious of the config file

/etc/apache2/vhosts.d/30_subversion_ssl_vhost.conf

When you remove the '-D SSL' you will cause all parts of the configuration files that are enclosed in ... to be skipped. The default SSL vhost file on my Gentoo box is wrapped in that tag so I wonder if, by removing the '-D SSL', you are preventing the config in 30_subversion_ssl_vhost.conf from being run at all and if that is what is allowing Apache to start.

If you temporarily remove the file 30_subversion_ssl_vhost.conf from /etc/apache2/vhosts.d does Apache run? Are there any other SSL related vhost.conf files in vhosts.d? My reasonably fresh/unused Apache install's vhosts.d directory looks like this:

# pwd && ls
/etc/apache2/vhosts.d
00_default_ssl_vhost.conf  00_default_vhost.conf  default_vhost.include

edit 1:

So much for that theory :) I am now wondering if the problem is with the Apache SSL setup itself. I apologize if I am covering ground you have already checked but I am wondering if you could do the following to help verify your Apache install.

On my Apache install with working SSL the use flags are as follows:

# emerge -av apache

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     U ] www-servers/apache-2.2.11-r2 [2.2.11] USE="ssl -debug -doc -ldap (-selinux) -sni -static -suexec -threads" APACHE2_MODULES="actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias -asis -auth_digest -authn_dbd -cern_meta -charset_lite -dbd -dumpio -ident -imagemap -log_forensic -proxy -proxy_ajp -proxy_balancer -proxy_connect -proxy_ftp -proxy_http -substitute -version" APACHE2_MPMS="-event -itk -peruser -prefork -worker" 64 kB

In particular do you have the 'ssl' USE flag set?

Also, could you use equery to verify the integrity of your apache2 install? If you do not have the equery command you can install it by running 'emerge -av gentoolkit'. The following command should verify the integrity of your apache install:

equery check apache

On my server the above command gives the following output:

[ Checking www-servers/apache-2.2.11 ]
!!! /etc/apache2/vhosts.d/00_default_ssl_vhost.conf has wrong mtime (is 1256620928, should be 1246793824)
!!! /etc/apache2/modules.d/00_default_settings.conf has wrong mtime (is 1246796304, should be 1246793824)
!!! /etc/conf.d/apache2 has incorrect md5sum
 * 429 out of 432 files good

edit 2:

Well the install looks good to me, so much for theory 2. I am wondering if we can coax Apache into giving some more information on startup. In /etc/conf.d/apache2 if you change your APACHE2_OPTS line from:

APACHE2_OPTS="-D DEFAULT_VHOST -D INFO -D SSL -D SSL_DEFAULT_VHOST -D LANGUAGE"

APACHE2_OPTS="-X -e debug -D DEFAULT_VHOST -D INFO -D SSL -D SSL_DEFAULT_VHOST -D LANGUAGE"

and then start Apache (/etc/init.d/apache2 start) the daemon should stay in the foreground (the -X flag) and output debuging messages as it starts (the -e debug option). Maybe this will give a clue as to why it is dying on startup.

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Solution for this Problem is pretty simple:

add to Proxypass:

BalancerMember ajp://10.176.201.9:8009 keepalive=On ttl=60

add to Tomcats Server.xml:

Connector port="8009" protocol="AJP/1.3" redirectPort="8443 connectionTimeout="60000"

After these changes everything should be work fine :-)

Best Answer

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