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OOM uses the Kubernetes service abstraction to provide a consistent access point for each of the ONAP components, independent of the pod or container architecture of that component. For example, the SDN-C component may introduce OpenDaylight clustering as some point and change the number of pods in this component to three or more, but this change will be isolated from the other ONAP components by the service abstraction. A service can include a load balancer on its ingress to distribute traffic between the pods and even react to dynamic changes in the number of pods if they are part of a replica set. A replica set is a construct that is used to describe the desired state of the cluster. For example 'replicas: 3' indicates to Kubernetes that a cluster of 3 instances is the desired state. Should one of the members of the cluster fail, a new member will be automatically started to replace it.
Some of the ONAP components many need a more deterministic deployment; for example to enable intra-cluster communication. For these applications the component can be deployed as a Kubernetes StatefulSet which will maintain a persistent identifier for the pods and thus a stable network id for the pods. For example: the pod names might be web-0, web-1, web-{N-1} for N 'web' pods with corresponding DNS entries such that intra service communication is simple even if the pods are physically distributed across multiple nodes. An example of how these capabilities can be used is described in the Running Consul on Kubernetes tutorial.
Anti-Affinity Rules
Assigning Pods to Nodes, Taints and Tolerations
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