IT teams can create and deploy network options for different Kubernetes environments with the help of Container Network Interface plugins. Find out how CNI works and make a list of the best network plugins.
Any enterprise platform needs to be able to grow and be optimized. Customizing a platform to meet the needs of a specific application or business without making permanent changes opens the door to new ideas and improvements while extending the life of the platform.
Kubernetes versions 1.25 and later use the Container Network Interface (CNI) to work with different network technologies and topologies to make the most of extensibility and optimization. At the moment, Kubernetes needs network plugins to support pods and run its network model.
Look more closely at how CNI works with Kubernetes and compare some of the most popular network plugins for Kubernetes, such as Calico, Flannel, Weave Net, Cilium, and Multus.
What is a Container Network Interface?
Container technology puts together, runs, and scales highly modular enterprise workloads by using virtual instances. Because containers need to talk to each other over enterprise and cloud networks, improving and optimizing network management can greatly improve the performance of both containers and applications.
At the time of publication, version 1.0.0, the CNI specification is a formal document that describes a networking method for Linux application containers that doesn’t depend on a specific vendor or technology. With the CNI plugin model, IT admins can create and deploy a wide range of network options for their containers. This lets them use Kubernetes in different networking environments.
Five parts of a container networking environment are defined by the CNI specification:
- the format used to define the network configuration, which includes network names, plugins to deploy, keys, and network object names;
- The protocol that is used by container runtimes like runc, CRI-O, and containerd to work together or talk to network plugins;
- the process for running plugins;
- the process for plugins to give other plugins functions or tasks; and
- The definitions of the data types that allow plugins to return results or send data to the runtime of the container.
When it is first made, a pod or container has no way to connect to a network. CNI plugins add a network interface to the namespace for the container network. Then, this virtual network connects hosts and containers, gives IP addresses, sets up routing, and does other things to set up the network environment so containers can talk to each other.
This is a very complicated process. In the context of containers and Kubernetes, the type of cluster networking used must be able to handle four different kinds of communication: pod-to-pod, pod-to-service, external-to-service, and tightly coupled container-to-container.
Kubernetes is in charge of sharing machines between applications, so it’s important to make sure that no two applications use the same ports and that ports on different systems work together. Kubernetes doesn’t try to solve these problems on its own; instead, it uses plugins, which makes Kubernetes less busy.
CNI is not a Kubernetes plugin. Instead, it is the specification that says how plugins should talk to the container runtime and work together. CNI plugins can be made and built in any way, and they often follow the same standards for making, testing, and delivering software as other projects. But in the end, plugins must follow the CNI specification in order to work with Kubernetes in a container environment.
The pros and cons of CNI plugins
Using a CNI plugin architecture has some of the following benefits:
Software that can be added to. With CNI plugins, developers don’t have to make software for every possible situation or environment where it will be used. Instead, businesses can just pick the plugin that works best for them.
Not getting locked in. Ideally, a plugin approach keeps businesses from being locked into one vendor and lets them use plugins made by anyone.
Simple changes. Businesses can make changes to the platform by installing new CNI plugins when deployment needs or environments change.
But CNI plugins aren’t perfect, and any platform that works with plugins can have problems. Before deploying any platform that needs plugins, businesses should think about these trade-offs:
Bugs no one expected. Developers of platforms don’t always test or validate plugins, which can lead to bugs, bad performance, and security issues. When testing or validating a software platform, its plugins should be taken into account. When a plugin is updated or replaced, the platform should be tested again for stability and performance.
More parts that move. Admins need to keep up with updates and patches not only for platforms like Kubernetes, but also for any plugins, which can make deploying and managing software harder.
Changing standards. Standards for plugins like CNI are not set in stone, and if something new happens, plugins may need to be changed. This could mean that the business needs new or updated plugins, which adds complexity and work. Also, there are no guarantees that important plugins will work with older versions of WordPress or that they will be updated quickly enough to meet new standards. All of these things can make business hard.
What’s next for CNI
CNI isn’t likely to change quickly in the near future because the current 1.0.0 specification meets a wide range of container network configuration needs. But the CNI standard could change over time to give more freedom and make it easier to adapt to changing network conditions.
For example, future versions of CNI might let existing network configurations be changed on the fly or let policies be changed on the fly in response to security needs, like firewall rules, or network performance needs.