Fleet was developed by the CoreOS company as a way of managing containers in CoreOS clusters. It is a low-level tool that other tools can build upon. Fleet has limits of approximately 100 nodes and 1,000 services. Having said that, for a small cluster, it can be just enough orchestration to meet the needs of your organization. It can also provide a solid base to build in-house processes.
Like all Docker orchestration tools, Fleet requires an overlay network. CoreOS ships with Flannel installed, but any Docker overlay network can be used. This includes the Docker native overlay and Weave Net. Overlay networks were described in Chapter 3, Cluster Building Blocks – Registry, Overlay Networks, and Shared Storage. It is important to note that neither Flannel nor Fleet provide any sort of service discovery. If that feature is needed, an overlay network which provides service discovery, such as Weave Net, may be used instead.