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In OpenShift Container Platform version 4.10, you can install a cluster on IBM Z and LinuxONE infrastructure that you provision in a restricted network.

While this document refers to only IBM Z, all information in it also applies to LinuxONE.

Additional considerations exist for non-bare metal platforms. Review the information in the guidelines for deploying OpenShift Container Platform on non-tested platforms before you install an OpenShift Container Platform cluster.

Prerequisites

About installations in restricted networks

In OpenShift Container Platform 4.10, you can perform an installation that does not require an active connection to the internet to obtain software components. Restricted network installations can be completed using installer-provisioned infrastructure or user-provisioned infrastructure, depending on the cloud platform to which you are installing the cluster.

If you choose to perform a restricted network installation on a cloud platform, you still require access to its cloud APIs. Some cloud functions, like Amazon Web Service’s Route 53 DNS and IAM services, require internet access. Depending on your network, you might require less internet access for an installation on bare metal hardware or on VMware vSphere.

To complete a restricted network installation, you must create a registry that mirrors the contents of the OpenShift Container Platform registry and contains the installation media. You can create this registry on a mirror host, which can access both the internet and your closed network, or by using other methods that meet your restrictions.

Because of the complexity of the configuration for user-provisioned installations, consider completing a standard user-provisioned infrastructure installation before you attempt a restricted network installation using user-provisioned infrastructure. Completing this test installation might make it easier to isolate and troubleshoot any issues that might arise during your installation in a restricted network.

Additional limits

Clusters in restricted networks have the following additional limitations and restrictions:

  • The ClusterVersion status includes an Unable to retrieve available updates error.

  • By default, you cannot use the contents of the Developer Catalog because you cannot access the required image stream tags.

Internet access for OpenShift Container Platform

In OpenShift Container Platform 4.10, you require access to the internet to obtain the images that are necessary to install your cluster.

You must have internet access to:

  • Access OpenShift Cluster Manager to download the installation program and perform subscription management. If the cluster has internet access and you do not disable Telemetry, that service automatically entitles your cluster.

  • Access Quay.io to obtain the packages that are required to install your cluster.

  • Obtain the packages that are required to perform cluster updates.

If your cluster cannot have direct internet access, you can perform a restricted network installation on some types of infrastructure that you provision. During that process, you download the required content and use it to populate a mirror registry with the installation packages. With some installation types, the environment that you install your cluster in will not require internet access. Before you update the cluster, you update the content of the mirror registry.

Machine requirements for a cluster with user-provisioned infrastructure

For a cluster that contains user-provisioned infrastructure, you must deploy all of the required machines.

One or more KVM host machines based on RHEL 8.4 or later. Each RHEL KVM host machine must have libvirt installed and running. The virtual machines are provisioned under each RHEL KVM host machine.

Required machines

The smallest OpenShift Container Platform clusters require the following hosts:

Table 1. Minimum required hosts
Hosts Description

One temporary bootstrap machine

The cluster requires the bootstrap machine to deploy the OpenShift Container Platform cluster on the three control plane machines. You can remove the bootstrap machine after you install the cluster.

Three control plane machines

The control plane machines run the Kubernetes and OpenShift Container Platform services that form the control plane.

At least two compute machines, which are also known as worker machines.

The workloads requested by OpenShift Container Platform users run on the compute machines.

To improve high availability of your cluster, distribute the control plane machines over different RHEL instances on at least two physical machines.

The bootstrap, control plane, and compute machines must use Red Hat Enterprise Linux CoreOS (RHCOS) as the operating system.

Network connectivity requirements

The OpenShift Container Platform installer creates the Ignition files, which are necessary for all the Red Hat Enterprise Linux CoreOS (RHCOS) virtual machines. The automated installation of OpenShift Container Platform is performed by the bootstrap machine. It starts the installation of OpenShift Container Platform on each node, starts the Kubernetes cluster, and then finishes. During this bootstrap, the virtual machine must have an established network connection either through a Dynamic Host Configuration Protocol (DHCP) server or static IP address.

IBM Z network connectivity requirements

To install on IBM Z under RHEL KVM, you need:

  • A RHEL KVM host configured with an OSA or RoCE network adapter.

  • Either a RHEL KVM host that is configured to use bridged networking in libvirt or MacVTap to connect the network to the guests.

Host machine resource requirements

The RHEL KVM host in your environment must meet the following requirements to host the virtual machines that you plan for the OpenShift Container Platform environment. See Getting started with virtualization.

You can install OpenShift Container Platform version 4.10 on the following IBM hardware:

  • IBM z16 (all models), IBM z15 (all models), IBM z14 (all models), IBM z13, and IBM z13s

  • LinuxONE, any version

Minimum IBM Z system environment

Hardware requirements

  • The equivalent of six Integrated Facilities for Linux (IFL), which are SMT2 enabled, for each cluster.

  • At least one network connection to both connect to the LoadBalancer service and to serve data for traffic outside the cluster.

You can use dedicated or shared IFLs to assign sufficient compute resources. Resource sharing is one of the key strengths of IBM Z. However, you must adjust capacity correctly on each hypervisor layer and ensure sufficient resources for every OpenShift Container Platform cluster.

Since the overall performance of the cluster can be impacted, the LPARs that are used to setup the OpenShift Container Platform clusters must provide sufficient compute capacity. In this context, LPAR weight management, entitlements, and CPU shares on the hypervisor level play an important role.

Operating system requirements

  • One LPAR running RHEL 8.4 or later with KVM, which is managed by libvirt

On your RHEL KVM host, set up:

  • Three guest virtual machines for OpenShift Container Platform control plane machines

  • Two guest virtual machines for OpenShift Container Platform compute machines

  • One guest virtual machine for the temporary OpenShift Container Platform bootstrap machine

Minimum resource requirements

Each cluster virtual machine must meet the following minimum requirements:

Virtual Machine Operating System vCPU [1] Virtual RAM Storage IOPS

Bootstrap

RHCOS

4

16 GB

100 GB

N/A

Control plane

RHCOS

4

16 GB

100 GB

N/A

Compute

RHCOS

2

8 GB

100 GB

N/A

  1. One physical core (IFL) provides two logical cores (threads) when SMT-2 is enabled. The hypervisor can provide two or more vCPUs.

Preferred IBM Z system environment

Hardware requirements

  • Three LPARS that each have the equivalent of six IFLs, which are SMT2 enabled, for each cluster.

  • Two network connections to connect to both connect to the LoadBalancer service and to serve data for traffic outside the cluster.

Operating system requirements

  • For high availability, two or three LPARs running RHEL 8.4 or later with KVM, which are managed by libvirt.

On your RHEL KVM host, set up:

  • Three guest virtual machines for OpenShift Container Platform control plane machines, distributed across the RHEL KVM host machines.

  • At least six guest virtual machines for OpenShift Container Platform compute machines, distributed across the RHEL KVM host machines.

  • One guest virtual machine for the temporary OpenShift Container Platform bootstrap machine.

  • To ensure the availability of integral components in an overcommitted environment, increase the priority of the control plane by using cpu_shares. Do the same for infrastructure nodes, if they exist. See schedinfo in IBM Documentation.

Preferred resource requirements

The preferred requirements for each cluster virtual machine are:

Virtual Machine Operating System vCPU Virtual RAM Storage

Bootstrap

RHCOS

4

16 GB

120 GB

Control plane

RHCOS

8

16 GB

120 GB

Compute

RHCOS

6

8 GB

120 GB

Certificate signing requests management

Because your cluster has limited access to automatic machine management when you use infrastructure that you provision, you must provide a mechanism for approving cluster certificate signing requests (CSRs) after installation. The kube-controller-manager only approves the kubelet client CSRs. The machine-approver cannot guarantee the validity of a serving certificate that is requested by using kubelet credentials because it cannot confirm that the correct machine issued the request. You must determine and implement a method of verifying the validity of the kubelet serving certificate requests and approving them.

Networking requirements for user-provisioned infrastructure

All the Red Hat Enterprise Linux CoreOS (RHCOS) machines require networking to be configured in initramfs during boot to fetch their Ignition config files.

During the initial boot, the machines require an IP address configuration that is set either through a DHCP server or statically by providing the required boot options. After a network connection is established, the machines download their Ignition config files from an HTTP or HTTPS server. The Ignition config files are then used to set the exact state of each machine. The Machine Config Operator completes more changes to the machines, such as the application of new certificates or keys, after installation.

It is recommended to use a DHCP server for long-term management of the cluster machines. Ensure that the DHCP server is configured to provide persistent IP addresses, DNS server information, and hostnames to the cluster machines.

If a DHCP service is not available for your user-provisioned infrastructure, you can instead provide the IP networking configuration and the address of the DNS server to the nodes at RHCOS install time. These can be passed as boot arguments if you are installing from an ISO image. See the Installing RHCOS and starting the OpenShift Container Platform bootstrap process section for more information about static IP provisioning and advanced networking options.

The Kubernetes API server must be able to resolve the node names of the cluster machines. If the API servers and worker nodes are in different zones, you can configure a default DNS search zone to allow the API server to resolve the node names. Another supported approach is to always refer to hosts by their fully-qualified domain names in both the node objects and all DNS requests.

Setting the cluster node hostnames through DHCP

On Red Hat Enterprise Linux CoreOS (RHCOS) machines, the hostname is set through NetworkManager. By default, the machines obtain their hostname through DHCP. If the hostname is not provided by DHCP, set statically through kernel arguments, or another method, it is obtained through a reverse DNS lookup. Reverse DNS lookup occurs after the network has been initialized on a node and can take time to resolve. Other system services can start prior to this and detect the hostname as localhost or similar. You can avoid this by using DHCP to provide the hostname for each cluster node.

Additionally, setting the hostnames through DHCP can bypass any manual DNS record name configuration errors in environments that have a DNS split-horizon implementation.

Network connectivity requirements

You must configure the network connectivity between machines to allow OpenShift Container Platform cluster components to communicate. Each machine must be able to resolve the hostnames of all other machines in the cluster.

This section provides details about the ports that are required.

In connected OpenShift Container Platform environments, all nodes are required to have internet access to pull images for platform containers and provide telemetry data to Red Hat.

Table 2. Ports used for all-machine to all-machine communications
Protocol Port Description

ICMP

N/A

Network reachability tests

TCP

1936

Metrics

9000-9999

Host level services, including the node exporter on ports 9100-9101 and the Cluster Version Operator on port 9099.

10250-10259

The default ports that Kubernetes reserves

10256

openshift-sdn

UDP

4789

VXLAN

6081

Geneve

9000-9999

Host level services, including the node exporter on ports 9100-9101.

500

IPsec IKE packets

4500

IPsec NAT-T packets

TCP/UDP

30000-32767

Kubernetes node port

ESP

N/A

IPsec Encapsulating Security Payload (ESP)

Table 3. Ports used for all-machine to control plane communications
Protocol Port Description

TCP

6443

Kubernetes API

Table 4. Ports used for control plane machine to control plane machine communications
Protocol Port Description

TCP

2379-2380

etcd server and peer ports

NTP configuration for user-provisioned infrastructure

OpenShift Container Platform clusters are configured to use a public Network Time Protocol (NTP) server by default. If you want to use a local enterprise NTP server, or if your cluster is being deployed in a disconnected network, you can configure the cluster to use a specific time server. For more information, see the documentation for Configuring chrony time service.

If a DHCP server provides NTP server information, the chrony time service on the Red Hat Enterprise Linux CoreOS (RHCOS) machines read the information and can sync the clock with the NTP servers.

Additional resources

User-provisioned DNS requirements

In OpenShift Container Platform deployments, DNS name resolution is required for the following components:

  • The Kubernetes API

  • The OpenShift Container Platform application wildcard

  • The bootstrap, control plane, and compute machines

Reverse DNS resolution is also required for the Kubernetes API, the bootstrap machine, the control plane machines, and the compute machines.

DNS A/AAAA or CNAME records are used for name resolution and PTR records are used for reverse name resolution. The reverse records are important because Red Hat Enterprise Linux CoreOS (RHCOS) uses the reverse records to set the hostnames for all the nodes, unless the hostnames are provided by DHCP. Additionally, the reverse records are used to generate the certificate signing requests (CSR) that OpenShift Container Platform needs to operate.

The following DNS records are required for a user-provisioned OpenShift Container Platform cluster and they must be in place before installation. In each record, <cluster_name> is the cluster name and <base_domain> is the base domain that you specify in the install-config.yaml file. A complete DNS record takes the form: <component>.<cluster_name>.<base_domain>..

Table 5. Required DNS records
Component Record Description

Kubernetes API

api.<cluster_name>.<base_domain>.

A DNS A/AAAA or CNAME record, and a DNS PTR record, to identify the API load balancer. These records must be resolvable by both clients external to the cluster and from all the nodes within the cluster.

api-int.<cluster_name>.<base_domain>.

A DNS A/AAAA or CNAME record, and a DNS PTR record, to internally identify the API load balancer. These records must be resolvable from all the nodes within the cluster.

The API server must be able to resolve the worker nodes by the hostnames that are recorded in Kubernetes. If the API server cannot resolve the node names, then proxied API calls can fail, and you cannot retrieve logs from pods.

Routes

*.apps.<cluster_name>.<base_domain>.

A wildcard DNS A/AAAA or CNAME record that refers to the application ingress load balancer. The application ingress load balancer targets the machines that run the Ingress Controller pods. The Ingress Controller pods run on the compute machines by default. These records must be resolvable by both clients external to the cluster and from all the nodes within the cluster.

For example, console-openshift-console.apps.<cluster_name>.<base_domain> is used as a wildcard route to the OpenShift Container Platform console.

Bootstrap machine

bootstrap.<cluster_name>.<base_domain>.

A DNS A/AAAA or CNAME record, and a DNS PTR record, to identify the bootstrap machine. These records must be resolvable by the nodes within the cluster.

Control plane machines

<master><n>.<cluster_name>.<base_domain>.

DNS A/AAAA or CNAME records and DNS PTR records to identify each machine for the control plane nodes. These records must be resolvable by the nodes within the cluster.

Compute machines

<worker><n>.<cluster_name>.<base_domain>.

DNS A/AAAA or CNAME records and DNS PTR records to identify each machine for the worker nodes. These records must be resolvable by the nodes within the cluster.

In OpenShift Container Platform 4.4 and later, you do not need to specify etcd host and SRV records in your DNS configuration.

You can use the dig command to verify name and reverse name resolution. See the section on Validating DNS resolution for user-provisioned infrastructure for detailed validation steps.

Example DNS configuration for user-provisioned clusters

This section provides A and PTR record configuration samples that meet the DNS requirements for deploying OpenShift Container Platform on user-provisioned infrastructure. The samples are not meant to provide advice for choosing one DNS solution over another.

In the examples, the cluster name is ocp4 and the base domain is example.com.

Example DNS A record configuration for a user-provisioned cluster

The following example is a BIND zone file that shows sample A records for name resolution in a user-provisioned cluster.

Sample DNS zone database
$TTL 1W
@	IN	SOA	ns1.example.com.	root (
			2019070700	; serial
			3H		; refresh (3 hours)
			30M		; retry (30 minutes)
			2W		; expiry (2 weeks)
			1W )		; minimum (1 week)
	IN	NS	ns1.example.com.
	IN	MX 10	smtp.example.com.
;
;
ns1.example.com.		IN	A	192.168.1.5
smtp.example.com.		IN	A	192.168.1.5
;
helper.example.com.		IN	A	192.168.1.5
helper.ocp4.example.com.	IN	A	192.168.1.5
;
api.ocp4.example.com.		IN	A	192.168.1.5 (1)
api-int.ocp4.example.com.	IN	A	192.168.1.5 (2)
;
*.apps.ocp4.example.com.	IN	A	192.168.1.5 (3)
;
bootstrap.ocp4.example.com.	IN	A	192.168.1.96 (4)
;
master0.ocp4.example.com.	IN	A	192.168.1.97 (5)
master1.ocp4.example.com.	IN	A	192.168.1.98 (5)
master2.ocp4.example.com.	IN	A	192.168.1.99 (5)
;
worker0.ocp4.example.com.	IN	A	192.168.1.11 (6)
worker1.ocp4.example.com.	IN	A	192.168.1.7 (6)
;
;EOF
1 Provides name resolution for the Kubernetes API. The record refers to the IP address of the API load balancer.
2 Provides name resolution for the Kubernetes API. The record refers to the IP address of the API load balancer and is used for internal cluster communications.
3 Provides name resolution for the wildcard routes. The record refers to the IP address of the application ingress load balancer. The application ingress load balancer targets the machines that run the Ingress Controller pods. The Ingress Controller pods run on the compute machines by default.

In the example, the same load balancer is used for the Kubernetes API and application ingress traffic. In production scenarios, you can deploy the API and application ingress load balancers separately so that you can scale the load balancer infrastructure for each in isolation.

4 Provides name resolution for the bootstrap machine.
5 Provides name resolution for the control plane machines.
6 Provides name resolution for the compute machines.
Example DNS PTR record configuration for a user-provisioned cluster

The following example BIND zone file shows sample PTR records for reverse name resolution in a user-provisioned cluster.

Sample DNS zone database for reverse records
$TTL 1W
@	IN	SOA	ns1.example.com.	root (
			2019070700	; serial
			3H		; refresh (3 hours)
			30M		; retry (30 minutes)
			2W		; expiry (2 weeks)
			1W )		; minimum (1 week)
	IN	NS	ns1.example.com.
;
5.1.168.192.in-addr.arpa.	IN	PTR	api.ocp4.example.com. (1)
5.1.168.192.in-addr.arpa.	IN	PTR	api-int.ocp4.example.com. (2)
;
96.1.168.192.in-addr.arpa.	IN	PTR	bootstrap.ocp4.example.com. (3)
;
97.1.168.192.in-addr.arpa.	IN	PTR	master0.ocp4.example.com. (4)
98.1.168.192.in-addr.arpa.	IN	PTR	master1.ocp4.example.com. (4)
99.1.168.192.in-addr.arpa.	IN	PTR	master2.ocp4.example.com. (4)
;
11.1.168.192.in-addr.arpa.	IN	PTR	worker0.ocp4.example.com. (5)
7.1.168.192.in-addr.arpa.	IN	PTR	worker1.ocp4.example.com. (5)
;
;EOF
1 Provides reverse DNS resolution for the Kubernetes API. The PTR record refers to the record name of the API load balancer.
2 Provides reverse DNS resolution for the Kubernetes API. The PTR record refers to the record name of the API load balancer and is used for internal cluster communications.
3 Provides reverse DNS resolution for the bootstrap machine.
4 Provid