The Gateway Engine component is deployed in each participating cluster and is responsible for establishing secure tunnels to other clusters.
The Gateway Engine has a pluggable architecture for the cable engine component that maintains the tunnels. The following implementations are available:
Instances of the Gateway Engine run on specifically designated nodes in a cluster of which there may be more than one for fault tolerance. Submariner supports active/passive High Availability for the Gateway Engine component, which means that there is only one active Gateway Engine instance at a time in a cluster. They perform a leader election process to determine the active instance and the others await in standby mode ready to take over should the active instance fail.
The Gateway Engine is deployed as a DaemonSet that is configured to only run on nodes labelled with “submariner.io/gateway=true”.
The active Gateway Engine communicates with the central Broker to advertise
Cluster resources to the other clusters connected to the
Broker, also ensuring that it is the sole
Endpoint for its cluster. The
Route Agent Pods running in the cluster learn about the
Endpoint and setup the necessary infrastructure to route cross-cluster
traffic from all nodes to the active Gateway Engine node. The active Gateway Engine
also establishes a watch on the Broker to learn about the active
Cluster resources advertised by the other clusters. Once two clusters are
aware of each other’s
Endpoints, they can establish a secure tunnel through
which traffic can be routed.
If the active Gateway Engine fails, another Gateway Engine on one of the
other designated nodes will gain leadership and perform reconciliation to
Endpoint and to ensure that it is the sole
remote clusters will learn of the new
Endpoint via the Broker and establish
a new tunnel. Similarly, the Route Agent Pods running in the local cluster
automatically update the route tables on each node to point to the new active
Gateway node in the cluster.
The impact on datapath for various scenarios in a KIND setup are captured in the following spreadsheet.