https://DevOpsCloud.io -- Cloud Monk Losang Jinpa, Ph.D., MCSE/MCT, GitOps DevOps Engineer

CNI (Container Network Interface) is a Cloud Native Computing Foundation project that provides a specification and libraries for writing plugins to configure network interfaces in Linux containers. It focuses solely on the network connectivity of containers and the release of allocated resources upon container deletion.

• **Specification and Libraries:** CNI offers a well-defined specification and libraries written in Go for creating plugins that handle network configuration in Linux containers.
• **Plugin Ecosystem:** CNI supports a wide range of network plugins, both open-source and closed-source, providing flexibility in choosing the right networking solution for your needs.
• **Focus on Network Connectivity:** CNI concentrates solely on establishing and managing network connections for containers, leaving other aspects like service discovery or load balancing to higher-level tools like Kubernetes.
• **Simplicity and Wide Adoption:** Due to its focused scope and clear specification, CNI has gained broad support and is simple to implement.
• **Integration with Container Runtimes:** CNI plugins are designed to work with various container runtimes, including Docker, containerd, and CRI-O.

• **Flexibility:** CNI's plugin architecture allows you to choose from a wide range of networking solutions, tailoring your network configuration to your specific requirements.
• **Simplicity:** Its focused scope and clear specification make CNI easy to understand and implement, both for plugin developers and users.
• **Portability:** CNI plugins can be used across different container runtimes and environments, promoting portability and avoiding vendor lock-in.
• **Community-Driven:** CNI is an open-source project with an active community, fostering collaboration and innovation in the container networking space.

CNI plugins are typically implemented in Go and interact with the container runtime through a standardized interface. Here's a conceptual example of a CNI plugin's `Add` function:

```go func CmdAdd(args *skel.CmdArgs) error {

   // Parse network configuration from args.StdinData
   netConf := ...

   // Create network interface and configure IP address
   interface := ...

   // Set up routing and any additional network configuration
   // ...

   // Return the result (including the assigned IP address)
   result := ¤t.Result{
       CNIVersion: current.ImplementedSpecVersion,
       Interfaces: []*current.Interface{interface},
       IPs:        []*current.IPConfig{ipConfig},
       // ... other fields ...
   }
   return result.Print()

This `Add` function receives network configuration data, creates a network interface, configures the IP address, and returns the result to the container runtime.

• **CNI Official Website:** s://www.cni.dev/(https://www.cni.dev/)
• **CNI GitHub Repository:** s://github.com/containernetworking/cni(https://github.com/containernetworking/cni)
• **CNI Specification:** s://github.com/containernetworking/cni/blob/master/SPEC.md(https://github.com/containernetworking/cni/blob/master/SPEC.md)