etcd modules (mods) are higher order pieces of functionality that only
speak to the client etcd API and are presented in the
/mod HTTP path
of the etcd service.
The basic idea is that etcd can ship things like dashboards, master election APIs and other helpful services that would normally have to stand up and talk to an etcd cluster directly in the binary. It is a convienence and hopefully eases complexity in deployments.
mod is the entry point to all of the etcd modules.