Submariner uses a central Broker component to facilitate the exchange of metadata information between Gateway Engines deployed in participating clusters. The Broker is basically a set of Custom Resource Definitions (CRDs) backed by the Kubernetes datastore. The Broker also defines a ServiceAccount and RBAC components to enable other Submariner components to securely access the Broker’s API.

While there no Services associated with the Broker, if using subctl to deploy the Broker, an operator Pod is also deployed that installs the CRDs and the Globalnet configuration.

Submariner defines two CRDs that are exchanged via the Broker: Endpoint and Cluster. The Endpoint CRD contains the information about the active Gateway Engine in a cluster, such as its IP, needed for clusters to connect to one another. The Cluster CRD contains static information about the originating cluster, such as its Service and Pod CIDRs.

The Broker is a singleton component that is deployed on a cluster whose Kubernetes API must be accessible by all of the participating clusters. If there is a mix of on-premises and public clusters, the Broker can be deployed on a public cluster. The Broker cluster may be one of the participating clusters or a standalone cluster without the other Submariner components deployed. The Gateway Engine components deployed in each participating cluster are configured with the information to securely connect to the Broker cluster’s API.

The availability of the Broker cluster does not affect the operation of the dataplane on the participating clusters, that is the dataplane will continue to route traffic using the last known information while the Broker is unavailable. However, during this time, control plane components will be unable to advertise new or updated information to other clusters and learn about new or updated information from other clusters. When connection is re-established to the Broker, each component will automatically re-synchronize its local information with the Broker and update the dataplane if necessary.