Imagine you get a call at 2 a.m. in the morning. The person on the other end asks, Hi, we are facing a difficult issue that is impacting production. We think it might be network-related. Can you check for us? Where would you check first? Of course, you would look at your monitoring tool and confirm whether any of the metrics changed in the last few hours. Throughout the book, we have been discussing various ways to programmatically make predictable changes to our network, with the goal of keeping the network running as smoothly as possible.

However, networks are not static. Far from it, they are probably one of the most fluent parts of the entire infrastructure. By definition, a network connects different parts together, constantly passing traffic back and forth. There are lots of moving parts that can cause your network to stop working...