In this recipe, we'll walk through the installation of Flannel. Flannel requires the installation of a key store and Flannel service. Due to the dependencies of each of these, they need to be configured as actual services on the Docker hosts. To do this, we'll leverage systemd
unit files to define each respective service.
In this example, we'll be using the same lab topology we used in Chapter 3, User-Defined Networks, where we discussed user-defined overlay networks:
You'll need a couple of hosts, preferably with some of them being on different subnets. It is assumed that the Docker hosts used in this lab are in their default configuration. In some cases, the changes we make may require you to have root-level access to the system.