Install squid caching server to reduce build time

Building using mock will trigger downloads of many RPMs from CentOS and Fedora mirrors each time the chroot initialized, which is often enough. If you install a caching proxy server, then RPMs are only downloaded once then cached on your local network. This will speed build times up substantially after running through a complete build once.

yum install squid

I recommend these settings in file /etc/squid/squid.conf for optimal caching

# 10G Cache
cache_dir ufs /var/spool/squid 10000 16 256
# Cache large files
maximum_object_size 512000 KB

Then call

service squid start
chkconfig squid on

To tell sipXecs build scripts to use your caching proxy, just add this configure switch when preparing to build sipXecs
./configure ... --with-yum-proxy=http://localhost:3128.

You can verify caching is working by your second build by looking for the string TCP_MEM_HIT in /var/log/squid/access.log.

You can use your new caching server to install systems faster as well. This is handy if you maintain a lot of systems, or test installations a lot. To use the proxy, edit /etc/yum.conf and add the setting proxy=http://your-squid-server:3128 to the [main] section.

Next you'll want to edit as many of the repository files as you can to use a fixed location for downloading. To do this, comment out the lines starting with mirrorlist= and uncomment out lines #baseurl. To automate editing of repos files to use base urls instead or mirror lists, this command should work.
sed -i -e 's/^mirrorlist/#mirrorlist/g' -e 's/^#baseurl/baseurl/g' /etc/yum.repos.d/*.repo

The reason you should use baseurls is so that you are consistently going to the same source for files and squid proxy will know to cache.
There is one issue, you must pick a mirror site that uses cache headers so squid knows caching is valid.