In this section, we will start our journey into high availability by exploring the concepts and building blocks of reliable and highly available systems. The million (trillion?) dollar question is how do we build reliable and highly available systems from unreliable components? Components will fail, you can take that to the bank; hardware will fail; networks will fail; configuration will be wrong; software will have bugs; people will make mistakes. Accepting that, we need to design a system that can be reliable and highly available even when components fail. The idea is to start with redundancy, detect component failure, and replace bad components quickly.