Chapter 2. Understanding OpenShift Service Mesh

The Istio resource is used to manage your Istio control planes. It is a cluster-wide resource, because the Istio control plane operates in and requires access to the entire cluster.

To select a namespace to run the control plane pods in, you can use the spec.namespace field.

You can access all Istio custom resource definition (CRD) options through spec.values fields:

apiVersion: sailoperator.io/v1alpha1
kind: Istio
metadata:
  name: default
spec:
  version: v1.22.3
  namespace: istio-system
  updateStrategy:
    type: InPlace
  values:
    pilot:
      resources:
        requests:
          cpu: 100m
          memory: 1024Mi

You can run the following command to see all the customization options:

$ oc explain istios.spec.values

To support canary updates of the control plane, OpenShift Service Mesh includes support for multiple Istio versions. You can select a version by setting spec.version to the version you would like to install, prefixed with a v. You can update to a new version just by changing this field.

OpenShift Service Mesh supports two different update strategies for your control planes:

After creating an Istio resource, OpenShift Service Mesh generates a revision name for the resource based on the updateStrategy, and creates a corresponding IstioRevision.

The IstioRevision is a cluster-wide resource and the lowest-level API OpenShift Service Mesh provides. It is usually not created by the user, but by the Operator itself. Its schema closely resembles that of the Istio resource - but instead of representing the state of a control plane you want to be present in your cluster, it represents a revision of that control plane.

A revision of the control plane you want to be present in your cluster is an instance of Istio with a specific version and revision name, and its revision name can be used to add workloads or entire namespaces to the mesh. For example: by using the istio.io/rev=<REVISION_NAME> label.

You can think of the relationship between the Istio and IstioRevision resources as similar to the relationship between Kubernetes' replica set and pod: a replica set can be created by users and results in the automatic creation of pods, which will trigger the instantiation of your containers.

Similarly, users create an Istio resource which instructs the OpenShift Service Mesh Operator to create a matching IstioRevision resource, which then in turn triggers the creation of the Istio control plane. To do that, the OpenShift Service Mesh Operator will copy all of your relevant configuration from the Istio resource to the IstioRevision resource.

The lifecycle of Istio’s Container Network Interface (CNI) plugin is managed separately when using OpenShift Service Mesh Operator. To install Istio’s CNI plugin, you create an IstioCNI resource.

The IstioCNI resource is a cluster-wide resource as it installs a daemon set that operates on all nodes of your cluster. You can select a version by setting the spec.version field, as you can see in the example that follows. To update the CNI plugin, change the version field to the version you want to install. Like the Istio resource, it also has a values field that exposes all of the options provided in the istio-cni chart:

apiVersion: sailoperator.io/v1alpha1
kind: IstioCNI
metadata:
  name: default
spec:
  version: v1.22.3
  namespace: istio-cni
  values:
    cni:
      cniConfDir: /etc/cni/net.d
      excludeNamespaces:
      - kube-system

In addition, Kiali depends on external services and components provided by the container application platform and Istio.

The Kiali console is integrated with OpenShift Service Mesh and provides the following capabilities:

The OpenShift Service Mesh Console (OSSMC) plugin is an OpenShift Container Platform plugin for Red Hat OpenShift Service Mesh. It integrates much of the Kiali Operator provided by Red Hat interface into the OpenShift Console, injecting both a Service Mesh main menu option with dedicated screens, as well as integrating Service Mesh tabs throughout console.

The OSSMC plugin is installed using Kiali Operator provided by Red Hat, and requires the Kiali Server component. OSSMC plugin has its own Custom Resource (CR) configuration.