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Linking Kubernetes clusters
Growing Pains
In legacy IT, dynamic scaling usually meant that you had to start new virtual machines manually. Then, you had to integrate the application into an existing cluster and possibly reconfigure the load balancers. Kubernetes takes all of this work off your plate. The
kubectl scale deployment/webserver --replicas=5
command tells Kubernetes to launch five instances of the web server container and makes sure they are running and reachable. Houston, we have load balancing.
The downside is that this only works as long as enough resources are left in the cluster. If the resources are exhausted, you need to add new nodes. Although this might be easy to set up, it means purchasing new hardware and facing a wait, during which the service is not available at the desired performance level. Moreover, if you use autoscaling, Kubernetes can reach its hardware limits without anyone noticing.
One way to bridge the resource gap is to migrate to a public cloud. In the simplest case, you just lease the required resources in the form of virtual machines (VMs) and link them to your cluster. To do this, the existing cluster and the nodes in the cloud need to be able to reach each other directly, either by public addresses or over a VPN connection. Another option is to federate Kubernetes clusters, which gives you the option of docking resources from a second, standalone cluster onto your own and running your applications on both. The software for this is available from the Kubernetes Cluster Federation project (KubeFed) [1].
Installation
In the following example, I assume you already operate a Kubernetes (K8s) cluster. The example uses a managed K8s cluster in the AWS cloud as the extension, but apart from the details of accessing it, the installation described here will work with any other Kubernetes cluster.
The
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