NetworkAttachment

NetworkAttachment is a term used in virtualization and container networking to describe the association of a compute resource, such as a container or virtual machine, with a network segment or network interface beyond the primary connection. It is a mechanism that enables multi-networking by attaching additional networks to the same resource, often to support isolation, policy application, or access to distinct traffic domains.

In Kubernetes environments, NetworkAttachment is commonly realized through the Multus CNI and related definitions. A NetworkAttachmentDefinition is a custom resource that specifies the configuration of an additional network (for example, VLAN, VXLAN, or a specific CNI plugin). A pod can declare one or more network attachments by referencing these definitions, typically via a Kubernetes annotation that lists the networks to attach. The result is the creation of secondary network interfaces (such as eth1, eth2) inside the pod’s network namespace, in addition to the default primary interface.

Other platforms and use cases also employ similar concepts. Virtualization stacks and cloud environments may use network attachments to attach VMs or containers to multiple networks, enabling features such as network segmentation, workload isolation, or access to specialized services. NetworkAttachment configurations can involve various underlying technologies, including different CNI plugins, VLANs, overlay networks, or SR-IOV-enabled interfaces, depending on the platform and policy requirements.

Key considerations for network attachments include correct permissioning, compatibility between CNIs, performance implications of multiple interfaces, and the management of network policies and security boundaries. Troubleshooting typically involves inspecting interface creation, attachment definitions, and accompanying CNI logs.