Architecture and dependencies of the service

Red Hat OpenShift master components

Review the following components in the IBM-managed master of your Red Hat OpenShift on IBM Cloud cluster.

You can't modify these components. IBM manages the components and automatically updates them during master patch updates.

In OpenShift Container Platform 4, many components are configured by a corresponding operator for ease of management. The following table discusses these operators and components together, to focus on the main functionality the component provides to the cluster.

Single tenancy

The master and all master components are dedicated only to you, and are not shared with other IBM customers.

Replicas

Master components, including the Red Hat OpenShift API server and etcd data store have three replicas and, if located in a multizone metro, are spread across zones for even higher availability. The master components are backed up every 8 hours.

cloud-controller-manager

The cloud controller manager manages cloud provider-specific components such as the IBM Cloud load balancer.

cluster-health

The cluster health component monitors the health of the cluster and integrates with IBM Cloud monitoring and metrics for the service.

cluster-policy-controller

The cluster-policy-controller maintains policy resources that are required to create pods within the cluster.

cluster-version-operator

The cluster version operator (CVO) installs and updates other operators that run in the cluster. For more information, see the GitHub project.

control-plane-operator

The control plane operator manages the installation and update of control plane components in the master.

etcd, etcd-molecule, etcd-operator

etcd is a highly available key value store that stores the state of all Kubernetes resources of a cluster, such as services, deployments, and pods. Data in etcd is backed up every 8 hours to an encrypted storage instance that IBM manages.

kube-controller-manager, openshift-controller-manager

The Kubernetes controller watches the state of objects within the cluster, such as the replica set of a workload. When the state of an object changes, for example if a pod in a replica set goes down, the controller manager initiates correcting actions to achieve the required state. The Red Hat OpenShift controller performs the same function for objects that are specific to the Red Hat OpenShift API, such as projects.

kube-scheduler

The Kubernetes scheduler watches for newly created pods and decides where to deploy them based on capacity, performance needs, policy constraints, anti-affinity specifications, and workload requirements. If no worker node can be found that matches the requirements, the pod is not deployed in the cluster.

manifests-bootstrapper

The manifests-boot-strapper job sets up the master with the required certificates to join as the master node of the cluster.

oauth-openshift

The built-in OAuth server is automatically set up to integrate with IBM Cloud Identity and Access Management (IAM). You can't add other supported identity providers to the cluster. For more information about how to authenticate with the cluster via IAM, see Accessing Red Hat OpenShift clusters.

openshift-apiserver, openshift-apiserver-operator, kube-apiserver

The API server is the main entry point for all cluster management requests from the worker node to the master. The API server validates and processes requests that change the state of Kubernetes objects, such as pods or services, and Red Hat OpenShift objects, such as projects or users. Then, the API server stores this state in the etcd data store.

konnectivity-server, konnectivity-operator

The Konnectivity server works with the Konnectivity agent to securely connect the master to the worker node. This connection supports apiserver proxy calls to your pods and services; oc exec, attach, and logs calls to the kubelet; and mutating and validating webhooks.

Admission controllers

Admission controllers are implemented for specific features in Red Hat OpenShift on IBM Cloud clusters. With admission controllers, you can set up policies in your cluster that determine whether a particular action in the cluster is allowed or not. In the policy, you can specify conditions when a user can't perform an action, even if this action is part of the general permissions that you assigned the user by using RBAC. Therefore, admission controllers can provide an extra layer of security for your cluster before an API request is processed by the Red Hat OpenShift API server. When you create a Red Hat OpenShift cluster, the following Kubernetes admission controllers are automatically installed in the given order in the Red Hat OpenShift master, which can't be changed by the user:

• NamespaceLifecycle
• LimitRanger
• ServiceAccount
• DefaultStorageClass
• ResourceQuota
• StorageObjectInUseProtection
• PersistentVolumeClaimResize
• Priority
• BuildByStrategy
• OriginPodNodeEnvironment
• PodNodeSelector
• ExternalIPRanger
• NodeRestriction
• SecurityContextConstraint
• SCCExecRestrictions
• PersistentVolumeLabel
• OwnerReferencesPermissionEnforcement
• PodTolerationRestriction
• openshift.io/JenkinsBootstrapper
• openshift.io/BuildConfigSecretInjector
• openshift.io/ImageLimitRange
• openshift.io/RestrictedEndpointsAdmission
• openshift.io/ImagePolicy
• openshift.io/IngressAdmission
• openshift.io/ClusterResourceQuota
• MutatingAdmissionWebhook
• ValidatingAdmissionWebhook

You can install your own admission controllers in the cluster or choose from the optional admission controllers that Red Hat OpenShift on IBM Cloud provides. Container image security enforcement: Install Portieris to block container deployments from unsigned images.

If you manually installed admission controllers and you don't want to use them anymore, make sure to remove them entirely. If admission controllers aren't entirely removed, they might block all actions that you want to perform on the cluster.

Red Hat OpenShift worker node components

Review the following components in the customer-managed worker nodes of your Red Hat OpenShift on IBM Cloud cluster.

These components run on your worker nodes because you are able to use them with the workloads that you deploy to your cluster. For example, your apps might use an operator from the OperatorHub that runs a container from an image in the internal registry. You are responsible for your usage of these components, but IBM provides updates for them in the worker node patch updates that you choose to apply.

In OpenShift Container Platform, many components are configured by a corresponding operator for ease of management. The following table discusses these operators and components together, to focus on the main functionality the component provides to the cluster.

Single tenancy

The worker nodes and all worker node components are dedicated only to you, and are not shared with other IBM customers. However, if you use worker node virtual machines, the underlying hardware might be shared with other IBM customers depending on the level of hardware isolation that you choose.

Operating System

For a list of supported operating systems by cluster version, see the Version information.

CRI-O container runtime

Your worker nodes are installed with CRI-O as the container runtime interface. For more information, see Container runtime.

Projects

Red Hat OpenShift organizes your resources into projects, which are Kubernetes namespaces with annotations, and includes many more components than community Kubernetes clusters to run Red Hat OpenShift features such as the catalog. Select components of projects are described in the following rows. For more information, see Working with projects.

calico-system, tigera-operator

Calico manages network policies for your cluster, and includes a few components to manage container network connectivity, IP address assignment, and network traffic control. The Tigera operator installs and manages the lifecycle of Calico components.

default

This project is used if you don't specify a project or create a project for your Kubernetes resources.

ibm-system

This project includes the ibm-cloud-provider-ip deployment that works with keepalived to provide health checking and Layer 4 load balancing for requests to app pods.

kube-system

This project includes many components that are used to run Kubernetes on the worker node.

• ibm-master-proxy: The ibm-master-proxy is a daemon set that forwards requests from the worker node to the IP addresses of the highly available master replicas. In single zone clusters, the master has three replicas on separate hosts. For clusters that are in a multizone-capable zone, the master has three replicas that are spread across zones. A highly available load balancer forwards requests to the master domain name to the master replicas.
• kubelet: The kubelet is a worker node agent that runs on every worker node and is responsible for monitoring the health of pods that run on the worker node and for watching the events that the API server sends. Based on the events, the kubelet creates or removes pods, ensures liveness and readiness probes, and reports back the status of the pods to the API server.
• vpn: The Konnectivity agent works with the Konnectivity server to securely connect the master to the worker node. This connection supports apiserver proxy calls to your pods and services, and oc exec, attach, and logs calls to the kubelet.
• Other components: The kube-system project also includes components to manage IBM-provided resources such as storage plug-ins for file and block storage, ingress application load balancer (ALB), and keepalived.

openshift-cloud-credential-operator

The cloud credential operator manages a controller for Red Hat OpenShift components that request cloud provider credentials. The controller ensures that only the credentials that are required for the operation are used, and not any elevated permissions like admin. For more information, see the GitHub project.

openshift-cluster-node-tuning-operator

IBM manages the node tuning operator, which runs a daemon set on each worker node in the cluster to tune worker nodes.

openshift-cluster-samples-operator

The samples operator manages select image streams and templates that come with the Red Hat OpenShift cluster by default. You can deploy these templates from the Developer perspective in the Red Hat OpenShift web console.

openshift-cluster-storage-operator

The cluster storage operator makes sure that a default storage class is set.

openshift-console, openshift-console-operator

The Red Hat OpenShift web console is a user-friendly, web-based interface that you can use to manage the Red Hat OpenShift and Kubernetes resources that run in your cluster. You can also use the console to display an oc login token to authenticate to your cluster from a CLI. For more information, see Navigating the Red Hat OpenShift console.

openshift-dns, openshift-dns-operator

The DNS project includes the components to validate incoming network traffic against the iptables rules that are set up on the worker node, and proxies requests that are allowed to enter or leave the cluster.

openshift-image-registry

Red Hat OpenShift provides an internal container image registry that you can use to locally manage and view images through the console. Alternatively, you can set up the private IBM Cloud Container Registry or import images from IBM Cloud Container Registry to the internal registry. The internal registry comes with a File Storage for Classic volume in your IBM Cloud infrastructure account to store the registry images. The file storage volume is provisioned through the image-registry-storage persistent volume claim (PVC).

openshift-ingress, openshift-ingress-operator

Red Hat OpenShift uses routes to directly expose an app's service on a hostname so that external clients can reach the service. To create routes, the cluster uses the Ingress operator. You can also use Ingress to expose apps externally and customize routing. Ingress consists of three components: the Ingress operator, Ingress controller, and Route resources. The Ingress controller maps the service to the hostname. By default, the Ingress controller includes two replicas. Make sure that your cluster has at least two worker nodes so that the Ingress controller can run on separate compute hosts for higher availability.

openshift-marketplace

The marketplace includes the OperatorHub that comes with the Red Hat OpenShift cluster by default. The OperatorHub includes operators from Red Hat and 3rd-party providers. Keep in mind that these operators are provided by the community, might not integrate with your cluster, and are not supported by IBM. You can enable operators from the OperatorHub in Red Hat OpenShift web console.

openshift-monitoring

OpenShift Container Platform includes a built-in monitoring stack for your cluster, that includes metrics and alert managing capabilities. For a comparison of the built-in monitoring stack and other options such as IBM Cloud Monitoring, see Understanding options for logging and monitoring.

openshift-multus

OpenShift Container Platform uses the Multus container network interface (CNI) plug-in to allow multiple pod networks. However, you can't configure the cluster to use multiple pod networks. Red Hat OpenShift on IBM Cloud clusters support only Calico, which is set up for your cluster by default. If enabled, Service Mesh uses the Multus plug-in.

openshift-network-operator

The cluster network operator (CNO) manages the cluster network components that are set up by default, such as the CNI pod network provider plug-in and DNS operator.

openshift-operator-lifecycle-manager

The operator lifecycle manager (OLM) manages the lifecycle of all operators and the catalog that run in the cluster, including the operators for the default components and any custom operators that you add.

openshift-service-ca, openshift-service-ca-operator

The certificate authority (CA) operator runs certificate signing and injects certificates into API server resources and configmaps in the cluster. For more information, see the GitHub project.

Cluster with public and private cloud service endpoints

The following diagram shows the components of your cluster and how they interact when both the public and private cloud service endpoints are enabled. Because both service endpoints are enabled, your VPC creates a public load balancer for each service for inbound traffic.

Cluster with private cloud service endpoint only

The following diagram shows the components of your cluster and how they interact when only the private cloud service endpoint is enabled. Because only the private cloud service endpoint is enabled, your VPC creates a private load balancer for each service for inbound traffic.

VPC master and worker node components

Masters and worker nodes include the same components as described in the Classic cluster architecture for clusters. For more information about the OpenShift Container Platform architecture, see the Red Hat OpenShift docs.

Master

Master components, including the API server and etcd, have three replicas and are spread across zones for even higher availability. Masters include the same components as described in the Classic cluster architecture for clusters. The master and all the master components are dedicated only to you, and are not shared with other IBM customers.

Worker node

With Red Hat OpenShift on IBM Cloud, the virtual machines that your cluster manages are instances that are called worker nodes. These worker nodes virtual machines and all the worker node components are dedicated to you only and are not shared with other IBM customers. However, the underlying hardware is shared with other IBM customers. You manage the worker nodes through the automation tools that are provided by Red Hat OpenShift on IBM Cloud, such as the API, CLI, or console. Unlike classic clusters, you don't see VPC compute worker nodes in your infrastructure portal or separate infrastructure bill, but instead manage all maintenance and billing activity for the worker nodes from Red Hat OpenShift on IBM Cloud.

Worker nodes include the same components as described in the Classic cluster architecture.

When you run oc get nodes, you might notice that the ROLES of your worker nodes are marked as both master,worker. These nodes are worker nodes in IBM Cloud, and don't include the master components that are managed by IBM. Instead, these nodes are marked as master because they run OpenShift Container Platform components that are required to set up and manage default resources within the cluster, such as the OperatorHub and internal registry.

Cluster networking

Your worker nodes are created in a VPC subnet in the zone that you specify. Communication between the master and worker nodes is over the private network. If you create a cluster with the public and private cloud service endpoints enabled, authenticated external users can communicate with the master over the public network, such as to run oc commands. If you create a cluster with only the private cloud service endpoints enabled, authenticated external users can communicate with the master over the private network only. You can set up your cluster to communicate with resources in on-premises networks, other VPCs, or classic infrastructure by setting up a VPC VPN, IBM Cloud Direct Link, or IBM Cloud Transit Gateway on the private network.

App networking

Virtual Private Cloud load balancers are automatically created in your VPC outside the cluster for any networking services that you create in your cluster. For example, a VPC load balancer exposes the router services in your cluster by default. Or, you can create a Kubernetes LoadBalancer service for your apps, and a VPC load balancer is automatically generated. VPC load balancers are multizone and route requests for your app through the private node ports that are automatically opened on your worker nodes. If the public and private cloud service endpoints are enabled, the routers and VPC load balancers are created as public by default. If only the private cloud service endpoint is enabled, the routers and VPC load balancers are created as private by default. For more information, see Public or Private app networking for VPC clusters. Calico is used as the cluster networking policy fabric.

Storage

You can set up IBM Cloud Object Storage and Cloud Databases only.