Kubernetes v1.6 introduced a new binary called
cloud-controller-manager is a daemon that embeds cloud-specific control loops. These cloud-specific control loops were originally in the
kube-controller-manager. Since cloud providers develop and release at a different pace compared to the Kubernetes project, abstracting the provider-specific code to the
cloud-controller-manager binary allows cloud vendors to evolve independently from the core Kubernetes code.
cloud-controller-manager can be linked to any cloud provider that satisfies cloudprovider.Interface. For backwards compatibility, the cloud-controller-manager provided in the core Kubernetes project uses the same cloud libraries as
kube-controller-manager. Cloud providers already supported in Kubernetes core are expected to use the in-tree cloud-controller-manager to transition out of Kubernetes core. In future Kubernetes releases, all cloud controller managers will be developed outside of the core Kubernetes project managed by sig leads or cloud vendors.
Every cloud has their own set of requirements for running their own cloud provider integration, it should not be too different from the requirements when running
kube-controller-manager. As a general rule of thumb you’ll need:
Successfully running cloud-controller-manager requires some changes to your cluster configuration.
kube-controller-managerMUST NOT specify the
--cloud-providerflag. This ensures that it does not run any cloud specific loops that would be run by cloud controller manager. In the future, this flag will be deprecated and removed.
kubeletmust run with
--cloud-provider=external. This is to ensure that the kubelet is aware that it must be initialized by the cloud controller manager before it is scheduled any work.
Keep in mind that setting up your cluster to use cloud controller manager will change your cluster behaviour in a few ways:
--cloud-provider=externalwill add a taint
node.cloudprovider.kubernetes.io/uninitializedwith an effect
NoScheduleduring initialization. This marks the node as needing a second initialization from an external controller before it can be scheduled work. Note that in the event that cloud controller manager is not available, new nodes in the cluster will be left unschedulable. The taint is important since the scheduler may require cloud specific information about nodes such as their region or type (high cpu, gpu, high memory, spot instance, etc).
As of v1.8, cloud controller manager can implement:
If you are using a cloud that is currently supported in Kubernetes core and would like to adopt cloud controller manager, see the cloud controller manager in kubernetes core.
For cloud controller managers not in Kubernetes core, you can find the respective projects in repos maintained by cloud vendors or sig leads.
For providers already in Kubernetes core, you can run the in-tree cloud controller manager as a Daemonset in your cluster, use the following as a guideline:
Running cloud controller manager comes with a few possible limitations. Although these limitations are being addressed in upcoming releases, it’s important that you are aware of these limitations for production workloads.
Cloud controller manager does not implement any of the volume controllers found in
kube-controller-manager as the volume integrations also require coordination with kubelets. As we evolve CSI (container storage interface) and add stronger support for flex volume plugins, necessary support will be added to cloud controller manager so that clouds can fully integrate with volumes. Learn more about out-of-tree CSI volume plugins here.
In the previous architecture for cloud providers, we relied on kubelets using a local metadata service to retrieve node information about itself. With this new architecture, we now fully rely on the cloud controller managers to retrieve information for all nodes. For very larger clusters, you should consider possible bottle necks such as resource requirements and API rate limiting.
The goal of the cloud controller manager project is to decouple development of cloud features from the core Kubernetes project. Unfortunately, many aspects of the Kubernetes project has assumptions that cloud provider features are tightly integrated into the project. As a result, adopting this new architecture can create several situations where a request is being made for information from a cloud provider, but the cloud controller manager may not be able to return that information without the original request being complete.
A good example of this is the TLS bootstrapping feature in the Kubelet. Currently, TLS bootstrapping assumes that the Kubelet has the ability to ask the cloud provider (or a local metadata service) for all its address types (private, public, etc) but cloud controller manager cannot set a node’s address types without being initialized in the first place which requires that the kubelet has TLS certificates to communicate with the apiserver.
As this initiative evolves, changes will be made to address these issues in upcoming releases.
To build and develop your own cloud controller manager, read the Developing Cloud Controller Manager doc.
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