The Cloud Controller Manager (CCM) is a specialized control plane component that integrates Kubernetes with the underlying cloud provider's APIs. It was introduced to decouple the core Kubernetes code from cloud-provider-specific code, making Kubernetes more modular and easier to maintain.

Key functions of the Cloud Controller Manager:

1. Node Controller:

• Checks with the cloud provider API to verify if a node has been deleted after it stops responding
• Updates node-specific cloud details like instance type, region, zones, etc.

1. Route Controller:

• Configures network routes in the cloud infrastructure
• Enables pod-to-pod communication across different nodes

1. Service Controller:

• Creates, updates, and deletes cloud provider load balancers when LoadBalancer-type services are created/modified/deleted
• Updates service status with load balancer details (IP addresses, hostnames)

Volume Controller (in some implementations):

• Manages cloud storage volumes (creation, attachment, mounting)
• Interacts with the cloud provider's storage APIs

Benefits of the CCM architecture:

1. Modularity: Cloud providers can develop and release features without modifying the core Kubernetes code
2. Maintenance: The core Kubernetes developers don't need to maintain cloud-specific code
3. Flexibility: You can run Kubernetes with no CCM (for on-premises), with the built-in CCM for supported providers, or with a custom CCM
4. Independence: Cloud providers can update their integrations on their own release cycles

Examples of cloud controller managers:

• AWS Cloud Controller Manager
• Azure Cloud Controller Manager
• GCP Cloud Controller Manager
• OpenStack Cloud Controller Manager
• vSphere Cloud Controller Manager

In a cloud-based Kubernetes deployment, the CCM is typically deployed as a DaemonSet or Deployment in the kube-system namespace. In self-hosted or bare-metal Kubernetes deployments, you might not use a CCM at all, or you might use a custom one for your infrastructure provider.

Before the CCM architecture, all cloud-specific code was embedded in the core Kubernetes components, which made maintenance challenging. The separation has been a significant improvement in the modularity of Kubernetes.