Ask an OpenShift Admin Office Hour - CNI plugins and Multus

Pods communicate with each other across the network, but how do they connect to the network? The Container Network Interface (CNI) provides a standardized way for network providers to allow Pods to connect. Red Hat OpenShift, via Multus, allows Pods to connect to more than one CNI at the same time. This week’s stream we were joined by three guests: Marc Curry, Product Manager for Red Hat OpenShift, along with Doug Smith and Tomo Hayashi, from the OpenShift engineering team. Together we had a discussion and exploration of CNI plugins, their function and purpose, how they interact with Pods, and some troubleshooting tips.

As always, please see the list below for additional links to specific topics, questions, and supporting materials for the episode!

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Episode 24 recorded stream:

Supporting links for today’s topic:

• Use this link to jump straight to where we begin talking about CNI and Multus.
• The list of CNI plugins tested with each OpenShift release is available here.

Other links and materials referenced during the stream:

• While we wait for the stable upgrade path for OpenShift 4.6 -> 4.7, this blog post is a fantastic overview of the release process which provides some insight into what we wait for, and why it sometimes takes a little while before upgrades are available.
• Did you know that compact clusters, i.e. a cluster with only three nodes where the control plane nodes are schedulable, can be deployed to any infrastructure using the non-integrated, platform agnostic install method?

Questions answered during the stream:

• What is a CNI plugin and how do they get used?
• Marc breaks down the CNI certification process for OpenShift here.
• If you’re curious about the Red Hat and partner supported CNI plugins available for OpenShift, you can hear us talk about them here.
• Unrelated to today’s topic, will the VMware CSI driver be added to OperatorHub?
• What is Multus?
• What’s the difference between a primary and secondary CNI plugin?
• What are some use cases for Multus?
• Which CRDs does Multus use and how do I configure them?
• Did you know that the default namespace is special for NetworkAttachmentDefinitions? A definition in the default namespace can be used by Pods in other namespaces!
• When an additional network is configured via the Network CRD, the NetworkAttachmentDefinition get’s created automatically?
• What is the function of the WhereAbouts and other CNI plugins in OpenShift?
• What can go wrong and how can I troubleshoot CNI?