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Private Networks

Private Networks can be used to communicate between servers over a dedicated network interface using IP addresses not available publicly.

The hcloud-cloud-controller-manager utilizes them for two features:

  1. Use the native routing capability of Private Networks in conjunction with your CNI and eliminate the overhead for an overlay network (e.g. VXLAN).
  2. Use private IP targets for LoadBalancers

Network Attachment Verification

When a network is configured, HCCM uses the metadata service to verify whether the specified network is attached to the node it’s running on. This behavior can be disabled by setting the environment variable:

HCLOUD_NETWORK_DISABLE_ATTACHED_CHECK=true

Node Object Updates

The controller automatically adds the server’s private IP address to the corresponding Kubernetes Node object under the InternalIP field.

Route Controller

The route controller is part of the HCCM and responsible for creating and deleting routes at Private Networks.

It is enabled by default, if a networking is enabled and a Private Network ID or name is provided. It can be disabled by setting HCLOUD_NETWORK_ROUTES_ENABLED to false.

To utilize this feature you need to use a CNI, which supports using the native routing capability of the infrastructure. As an example, Cilium can be set to use the routing-mode: native.

IP Range Considerations

When using the route controller you need to make some considerations on the IP ranges for the cluster and service CIDR. By default, Kubernetes will allocate a /24 subnet for each node. Depending on the amount of nodes you plan to add to the cluster you need to choose your cluster CIDR accordingly.

Example Values

  • Private Network IP range: 10.0.0.0/8
  • Subnet for Cloud Servers & Load Balancers: 10.0.0.0/24
  • Cluster CIDR: 10.244.0.0/16
  • Service CIDR: 10.43.0.0/16