gmetad-rrdcached-centos7

Solving heavy I/O on gmetad server by adding rrdcached on CentOS7.

Rrdcached is part of rrdtool:

# which rrdtool
/usr/bin/rrdtool
# rpm -qf `which rrdtool`
rrdtool-1.4.8-9.el7.x86_64
# rrdtool -v
RRDtool 1.4.8  Copyright 1997-2013 by Tobias Oetiker <tobi@oetiker.ch>
              Compiled Nov 20 2015 19:23:48

Running rrdcached

Step by step from: https://github.com/ganglia/monitor-core/wiki/Integrating-Ganglia-with-rrdcached

BUT! :-)

Apache on CentOS 7 comes with sneaky line in systemd configfile:

PrivateTmp=true

which prevents using /tmp/ for rrdcached sockets.

So let's move it, but we'd need suitable directory - or we can use another systemd directives and maintain our own under /run:

RuntimeDirectory=rrdcached
RuntimeDirectoryMode=0755

Cool. Now we need to tell gmetad to use rrdcache. Gmetad on CentOS doesn't use /etc/sysconfig/gmetad by default, so we need to enhance systemd unitfile to do so:

mkdir /etc/systemd/system/gmetad.service.d/
cat > /etc/systemd/system/gmetad.service.d/gmetad-envfile.conf <<_EOF
[Service]
EnvironmentFile=/etc/sysconfig/gmetad
_EOF
systemctl daemon-reload
systemctl restart gmetad

Last thing, we just add

$conf['rrdcached_socket'] = "unix:/var/run/rrdcached/rrdcached.limited.sock";

to Ganglia web conf.php and restart all.