This document discusses how open source software is key to building clouds. It describes the different types of cloud computing models including Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS). It then outlines some popular open source tools that can be used to provision infrastructure, configure systems, automate tasks, and monitor clouds including hypervisors like KVM and Xen, automation tools like Ansible and Chef, and monitoring tools like Nagios and Zabbix. Finally, it proposes a conceptual automated toolchain for managing clouds using these various open source management tools.