High availability

In order to ensure high availability (HA) of a control plane, both global and zone, you can deploy more than one replica.

Each replica should be behind a load balancer such that requests to the control plane API are distributed across the replicas.

On Kubernetes this is handled using a Deployment and a Service. When your control plane isn’t deployed on Kubernetes, it’s up to you to handle this within your infrastructure.

Leader

Control planes also perform tasks independent of API requests. To avoid conflicts, each of these tasks needs to be performed by only one instance at a time, by the leader.

For each logical control plane, the instances work together to ensure there’s only one leader at a time. When the control planes are running in universal mode, this is handled by the leader maintaining a lock on the database. In Kubernetes mode, it’s handled similarly but uses the built-in coordination API resources.

An example of a leader task is that every zone control plane leader maintains a connection to the global control plane in order to:

• send relevant changes in the zone to the global control plane
• receive and act on relevant updates about the global state