While building applications that can talk among themselves on the same machine can be cool, eventually, we'll need to talk to external systems. Most of these systems will be browsers in our case, but they may be other servers. Since we can't use named pipes/Unix domain sockets over these channels, we need to use various protocols of a network.
Technically, we could still use the preceding two concepts across servers by utilizing shared drives/filesystem sharing, but this isn't a good idea. We've already shown that we can change the listen method from pointing to a file to pointing to a port. In the worst case, we can use a shared filesystem, but it is nowhere near optimal and it should be converted into utilizing one of the protocols we'll cover here.
The protocols that we will focus on are the two low-level protocols known as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). We will also take a look at the higher-level protocol of the web: Hyper Text Transfer Protocol version 2 (HTTP/2). With these protocols, we will be able to create highly available applications that can be accessed over a network.