KUMA Core availability under various scenarios

KUMA Core availability in various scenarios:

• Malfunction or network disconnection of the worker node where the KUMA Core service is deployed.

  Access to the KUMA web interface is lost. After 6 minutes, Kubernetes initiates migration of the Core bucket to an operational node of the cluster. After the deployment, which takes less than one minute, is completed, the KUMA web interface becomes available again at URLs based on the FQDN of the load balancer. To determine on which of the hosts the Core is running, run the following command in the terminal of one of the controllers:

  k0s kubectl get pod -n kuma -o wide

  When the malfunctioning worker node or access to it is restored, the Core bucket is not migrated from its current worker node. The recovered node can participate in the replication of the Core service's disk volume.

• A worker node that contains a replica of the KUMA Core disk, and which is not hosting the Core service at the moment, fails or loses network connectivity.

  The KUMA web interface remains available at URLs based on the FQDN of the load balancer. The network storage creates a replica of the running Core disk volume on other running nodes. There is also no disruption of access to KUMA at URLs based on the FQDNs of currently operational nodes.

• Loss of availability of one or more cluster controllers when quorum is maintained.

  Worker nodes work normally. Access to KUMA is not disrupted. A failure of cluster controllers extensive enough to break quorum leads to the loss of control over the cluster.

  Correspondence of the number of machines in use to ensure high availability

  Number of controllers when installing a cluster	Minimum number of controllers required for the operation of the cluster (quorum)	Admissible number of failed controllers
  1	1	0
  2	2	0
  3	2	1
  4	3	1
  5	3	2
  6	4	2
  7	4	3
  8	5	3
  9	5	4

• Simultaneous failure of all Kubernetes cluster controllers.

  The cluster cannot be managed and therefore will have impaired performance.

• Simultaneous loss of availability of all worker nodes of a cluster with replicas of the Core volume and the Core pod.

  Access to the KUMA web interface is lost. If all replicas are lost, information will be lost.

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