K8 LB Networking

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I understand what the Loadbalancer service type does. i.e it creates spins up a LB instance in your cloud instance, NodePorts are created and traffic is sent to the VIP onto the NodePorts.

However, how does this actually work in terms of kubectl and the LB spin up. Is this a construct within the CNI? What part of K8 sends the request and instructs the cloud provider to create the LB?


1 Answers

Blokje5 On

In this case the CloudControllerManager is responsible for the creation. The CloudControllerManager contains a ServiceController that listens to Service Create/Update/Delete events and triggers the creation of a LoadBalancer based on the configuration of the Service.

In general in Kubernetes you have the concept of declaratively creating a Resource (such as a Service), of which the state is stored in State Storage (etcd in Kubernetes). The controllers are responsible for making sure that that state is realised. In this case the state is realised by creating a Load Balancer in a cloud provider and pointing it to the Kubernetes Cluster.