Introduction to CNI Plugins
The Container Network Interface (CNI) is a specification for configuring network interfaces for Linux containers. It is used by Kubernetes to configure the network for pods. There are a number of different CNI plugins available, each of which provides a different set of features.
This article will provide a technical comparison of two of the most popular CNI plugins for Kubernetes: Calico and Flannel.
Calico
Calico is a CNI plugin that provides a high-performance and scalable network for Kubernetes. It is a pure Layer 3 network, and it uses BGP to route traffic between pods. This makes Calico a very efficient and scalable CNI plugin.
Calico Architecture
The Calico architecture is made up of a number of different components:
- Felix: Felix is a daemon that runs on each node in the Kubernetes cluster. It is responsible for programming the network on the node.
- BGP Speaker: The BGP speaker is responsible for advertising the routes to the pods on the node to the other nodes in the cluster.
- etcd: etcd is a distributed key-value store that is used to store the state of the Calico network.
Calico Features
Calico provides a number of features, including:
- High performance: Calico is a very high-performance CNI plugin. It can achieve line-rate performance with a very low latency.
- Scalability: Calico is a very scalable CNI plugin. It can support thousands of nodes and tens of thousands of pods.
- Security: Calico provides a number of security features, including network policies and encryption.
- Interoperability: Calico is interoperable with a wide range of other networking solutions, such as Istio and MetalLB.
Flannel
Flannel is a CNI plugin that provides a simple and easy-to-use network for Kubernetes. It is a Layer 2 network, and it uses a variety of different backends to route traffic between pods.
Flannel Architecture
The Flannel architecture is made up of a number of different components:
- flanneld: flanneld is a daemon that runs on each node in the Kubernetes cluster. It is responsible for creating a virtual network for the pods on the node.
- etcd: etcd is a distributed key-value store that is used to store the state of the Flannel network.
Flannel Backends
Flannel supports a variety of different backends, including:
- VXLAN: VXLAN is a network virtualization overlay technology that encapsulates Layer 2 Ethernet frames in Layer 3 UDP packets.
- host-gw: host-gw is a backend that uses the host’s routing table to route traffic between pods.
- UDP: UDP is a backend that uses UDP to route traffic between pods.
Flannel Features
Flannel provides a number of features, including:
- Simplicity: Flannel is a very simple and easy-to-use CNI plugin.
- Flexibility: Flannel supports a variety of different backends, which makes it a very flexible CNI plugin.
- Interoperability: Flannel is interoperable with a wide range of other networking solutions.
Calico vs. Flannel
| Feature | Calico | Flannel |
|---|---|---|
| Network Model | Layer 3 | Layer 2 |
| Routing | BGP | VXLAN, host-gw, UDP |
| Performance | High | Medium |
| Scalability | High | Medium |
| Security | High | Medium |
| Simplicity | Medium | High |
Conclusion
Calico and Flannel are two of the most popular CNI plugins for Kubernetes. They both have their own strengths and weaknesses. Calico is a good choice for users who need a high-performance and scalable network. Flannel is a good choice for users who need a simple and easy-to-use network. The best CNI plugin for you will depend on your specific needs.