Choosing a CNI Plugin: Calico vs Cilium vs Flannel vs Cloud-Native CNI

Choosing a CNI Plugin#

The Container Network Interface (CNI) plugin is one of the most consequential infrastructure decisions in a Kubernetes cluster. It determines how pods get IP addresses, how traffic flows between them, whether network policies are enforced, and what observability you get into network behavior. Changing CNI after deployment is painful – it typically requires draining and rebuilding nodes, or rebuilding the cluster entirely. Choose carefully up front.

Multi-Cloud Networking Patterns

Multi-Cloud Networking Patterns#

Multi-cloud networking connects workloads across two or more cloud providers into a coherent network. The motivations vary – vendor redundancy, best-of-breed service selection, regulatory requirements – but the challenges are the same: private connectivity between isolated networks, consistent service discovery, and traffic routing that handles failures.

VPN Tunnels Between Clouds#

IPsec VPN tunnels are the simplest way to connect two cloud networks. Each provider offers managed VPN gateways that terminate IPsec tunnels, encrypting traffic between VPCs without exposing it to the public internet.

Cloud Networking Fundamentals: VPCs, Subnets, Security Groups, and Connectivity

VPC Concepts#

A Virtual Private Cloud is an isolated virtual network inside a cloud provider. Every resource you launch – EC2 instances, RDS databases, Lambda functions with VPC access – lives inside a VPC. The VPC defines an IP address range using CIDR notation, and all resources within it get addresses from that range.

The most common mistake is giving every VPC a /16 (65,536 addresses). This wastes IP space and causes problems later when you need to peer VPCs – overlapping CIDR blocks cannot be peered. Plan your IP allocation before building anything.