This simple configuration consists of a single messaging engine running on one server only.
This configuration has a single messaging engine with no provision for either workload sharing or high availability. If the server on which the messaging engine is running fails, the messaging engine cannot be failed over to an alternative server. This configuration is most easily achieved by adding a server to a bus. Alternatively you could add a cluster to the bus and configure a Static policy for the messaging engine.
The diagram below shows a simple configuration that has been created by adding a server to a bus. There is a single messaging engine, ME, with data store DS, running on one server. If the server fails the messaging engine becomes unavailable until the server can be restarted.
The data store for the messaging engine only needs to be accessible by this single server, as no other server can run the messaging engine.