Instances are the basic blocks that make up our system. They’re like cobblestone Minecraft blocks—not that interesting by themselves, but we can make amazing things out of them. If we do a good job of building code to run in instances, then we can make a solid large-scale structure. That means instances should be designed for production. We’ve seen how to make them deployable, configurable, and monitorable. Now we need to look at how we can connect instances together into a whole system. This “interconnect” layer provides many of our most important mechanisms for availability and security, yet it often gets overlooked. In the next chapter we’ll see how to design this important layer for production.