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Quickstart Guide

This guide is intended as a way to get you off the ground, and using Multus CNI to create Kubernetes pods with multiple interfaces. If you're already using Multus and need more detail, see the comprehensive usage guide. This document a quickstart and a getting started guide in one, intended for your first run-through of Multus CNI.

We'll first install Multus CNI, and then we'll setup some configurations so that you can see how multiple interfaces are created for pods.

Key Concepts

Two things we'll refer to a number of times through this document are:

  • "Default network" -- This is your pod-to-pod network. This is how pods communicate among one another in your cluster, how they have connectivity. Generally speaking, this is presented as the interface named eth0. This interface is always attached to your pods, so that they can have connectivity among themselves. We'll add interfaces in addition to this.
  • "CRDs" -- Custom Resource Definitions. Custom Resources are a way that the Kubernetes API is extended. We use these here to store some information that Multus can read. Primarily, we use these to store the configurations for each of the additional interfaces that are attached to your pods.

Installation

Our recommended quickstart method to deploy Multus is to deploy using a Daemonset. This method is provided in this guide along with Flannel. Flannel is deployed as a pod-to-pod network that is used as our "default network" -- this provides connectivity between pods in your cluster. Each additional network attachment (i.e. for multiple interfaces in pods) is made in addition to this default network. This guide generally assumes a new Kubernetes cluster that hasn't yet had any networking configured. If it's your first time using Multus, you might consider using a fresh cluster to learn with, and then later configure it to work with an existing cluster.

Firstly, clone this GitHub repository.

git clone https://github.com/intel/multus-cni.git && cd multus-cni

We'll apply files to kubectl from this repo. The files we're applying here specify a "Daemonset" (pods that run on each node in the cluster), this Daemonset handles installing the Multus CNI binary, dropping a default configuration on each node in the cluster -- and then also installs Flannel to use as a default network.

$ cat ./images/{multus-daemonset.yml,flannel-daemonset.yml} | kubectl apply -f -

Note: For crio runtime use multus-crio-daemonset.yml (crio uses /usr/libexec/cni as default path for plugin directory). Before deploying daemonsets,delete all default network plugin configuration files under /etc/cni/net.d If the runtime is cri-o, then apply these files.

$ cat ./images/{multus-crio-daemonset.yml,flannel-daemonset.yml} | kubectl apply -f -

Validating your installation

Generally, the first step in validating your installation is to look at the STATUS field of your nodes, you can check it out by looking at:

$ kubectl get nodes

This will show each of the nodes in your cluster, take a look at the STATUS field, and look for Ready to appear for each of your nodes. This readiness is determined by the presence of a CNI configuration file on each of the nodes, and when that file appears.

You may also wish to start any pod in your cluster (without any further configuration), and validate that it works as you'd otherwise expect -- especially that it can communicate over the default network.

Creating additional interfaces

The first thing we'll do is create configurations for each of the additional interfaces that we attach to pods. We'll do this by creating Custom Resources. Part of the quickstart installation creates a "CRD" -- a custom resource definition that is the home where we keep these custom resources -- we'll store our configurations for each interface in these.

CNI Configurations

Each configuration we'll add is a CNI configuration. If you're not familiar with them, let's break them down quickly. Here's an example CNI configuration:

{
  "cniVersion": "0.3.0",
  "type": "loopback",
  "additional": "information"
}

CNI configurations are JSON, and we have a structure here that has a few things we're interested in:

  1. cniVersion: Tells each CNI plugin which version is being used and can give the plugin information if it's using a too late (or too early) version.
  2. type: This tells CNI which binary to call on disk. Each CNI plugin is a binary that's called. Typically, these binaries are stored in /opt/cni/bin on each node, and CNI executes this binary. In this case we've specified the loopback binary (which create a loopback-type network interface). If this is your first time installing Multus, you might want to verify that the plugins that are in the "type" field are actually on disk in the /opt/cni/bin directory.
  3. additional: This field is put here as an example, each CNI plugin can specify whatever configuration parameters they'd like in JSON. These are specific to the binary you're calling in the type field.

For an even further example -- take a look at the bridge CNI plugin README which shows additional

If you'd like more information about CNI configuration, you can read the entire CNI specification. It might also be useful to look at the CNI reference plugins and see how they're configured.

You do not need to reload or refresh the Kubelets when CNI configurations change. These are read on each creation & deletion of pods. So if you change a configuration, it'll apply the next time a pod is created. Existing pods may need to be restarted if they need the new configuration.

Storing a configuration as a Custom Resource

So, we want to create an additional interface. Let's create a macvlan interface for pods to use. We'll create a custom resource that defines the CNI configuration for interfaces.

Note in the following command that there's a kind: NetworkAttachmentDefinition. This is our fancy name for our configuration -- it's a custom extension of Kubernetes that defines how we attach networks to our pods.

Secondarily, note the config field. You'll see that this is a CNI configuration just like we explained earlier.

Lastly but very importantly, note under metadata the name field -- here's where we give this configuration a name, and it's how we tell pods to use this configuration. The name here is macvlan-conf -- as we're creating a configuration for macvlan.

Here's the command to create this example configuration:

cat <<EOF | kubectl create -f -
apiVersion: "k8s.cni.cncf.io/v1"
kind: NetworkAttachmentDefinition
metadata:
  name: macvlan-conf
spec:
  config: '{
      "cniVersion": "0.3.0",
      "type": "macvlan",
      "master": "eth0",
      "mode": "bridge",
      "ipam": {
        "type": "host-local",
        "subnet": "192.168.1.0/24",
        "rangeStart": "192.168.1.200",
        "rangeEnd": "192.168.1.216",
        "routes": [
          { "dst": "0.0.0.0/0" }
        ],
        "gateway": "192.168.1.1"
      }
    }'
EOF

NOTE: This example uses eth0 as the master parameter, this master parameter should match the interface name on the hosts in your cluster.

You can see which configurations you've created using kubectl here's how you can do that:

kubectl get network-attachment-definitions

You can get more detail by describing them:

kubectl describe network-attachment-definitions macvlan-conf

Creating a pod that attaches an additional interface

We're going to create a pod. This will look familiar as any pod you might have created before, but, we'll have a special annotations field -- in this case we'll have an annotation called k8s.v1.cni.cncf.io/networks. This field takes a comma delimited list of the names of your NetworkAttachmentDefinitions as we created above. Note in the comand below that we have the annotation of k8s.v1.cni.cncf.io/networks: macvlan-conf where macvlan-conf is the name we used above when we created our configuration.

Let's go ahead and create a pod (that just sleeps for a really long time) with this command:

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: samplepod
  annotations:
    k8s.v1.cni.cncf.io/networks: macvlan-conf
spec:
  containers:
  - name: samplepod
    command: ["/bin/bash", "-c", "sleep 2000000000000"]
    image: dougbtv/centos-network
EOF

You may now inspect the pod and see what interfaces interfaces are attached, like so:

$ kubectl exec -it samplepod -- ip a

You should note that there's 3 interfaces:

  • lo a loopback interface
  • eth0 our default network
  • net1 the new interface we created with the macvlan configuration.

What if I want more interfaces?

You can add more interfaces to a pod by creating more custom resources and then referring to them in pod's annotation. You can also reuse configurations, so for example, to attach two macvlan interfaces to a pod, you could create a pod like so:

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: samplepod
  annotations:
    k8s.v1.cni.cncf.io/networks: macvlan-conf,macvlan-conf
spec:
  containers:
  - name: samplepod
    command: ["/bin/bash", "-c", "sleep 2000000000000"]
    image: dougbtv/centos-network
EOF

Note that the annotation now reads k8s.v1.cni.cncf.io/networks: macvlan-conf,macvlan-conf. Where we have the same configuration used twice, separated by a comma.

If you were to create another custom resource with the name foo you could use that such as: k8s.v1.cni.cncf.io/networks: foo,macvlan-conf, and use any number of attachments.

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