How to install dpkg-reconfigure?

dpkg-reconfigure is provided by the debconf package, which should always be installed in any Ubuntu 12.04 install. If it's not, use:

sudo apt-get install debconf

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In your case, you are running Amazon's AMI Linux which is based on CentOS, not Ubuntu. That's why apt-get or dpkg-reconfgure, which are native to Debian/Ubuntu, are not available on your EC2 instance.