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Chapter 2. Prerequisites

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The Assisted Installer validates the following prerequisites to ensure successful installation.

If you use a firewall, you must configure it so that Assisted Installer can access the resources it requires to function.

2.1. Supported CPU architectures

The Assisted Installer is supported on the following CPU architectures:

  • x86_64
  • arm64
  • ppc64le
  • s390x

2.2. Resource requirements

This section describes the resource requirements for different clusters and installation options.

The multicluster engine for Kubernetes requires additional resources.

If you deploy the multicluster engine with storage, such as OpenShift Data Foundation or LVM Storage, you must also assign additional resources to each node.

2.2.1. Multi-node cluster resource requirements

The resource requirements of a multi-node cluster depend on the installation options.

Multi-node cluster basic installation

  • Control plane nodes:

    • 4 CPU cores
    • 16 GB RAM

    • 100 GB storage

      Note

      The disks must be reasonably fast, with an etcd wal_fsync_duration_seconds p99 duration that is less than 10 ms. For more information, see the Red Hat Knowledgebase solution How to Use 'fio' to Check Etcd Disk Performance in OCP.

  • Compute nodes:

    • 2 CPU cores
    • 8 GB RAM
    • 100 GB storage
Multi-node cluster + multicluster engine
  • Additional 4 CPU cores

  • Additional 16 GB RAM

    Note

    If you deploy multicluster engine without OpenShift Data Foundation, no storage is configured. You configure the storage after the installation.

Multi-node cluster + multicluster engine + OpenShift Data Foundation or LVM Storage
  • Additional 75 GB storage

2.2.2. Single-node OpenShift resource requirements

The resource requirements for single-node OpenShift depend on the installation options.

Single-node OpenShift basic installation
  • 8 CPU cores
  • 16 GB RAM
  • 100 GB storage
Single-node OpenShift + multicluster engine
  • Additional 8 CPU cores

  • Additional 32 GB RAM

    Note

    If you deploy multicluster engine without OpenShift Data Foundation, LVM Storage is enabled.

Single-node OpenShift + multicluster engine + OpenShift Data Foundation or LVM Storage
  • Additional 95 GB storage

2.3. Networking requirements

For hosts of type VMware, set clusterSet disk.enableUUID to true, even when the platform is not vSphere.

2.3.1. General networking requirements

The network must meet the following requirements:

  • A DHCP server unless using static IP addressing.

  • A base domain name. You must ensure that the following requirements are met:

    • There is no wildcard, such as *.<cluster_name>.<base_domain>, or the installation will not proceed.
    • A DNS A/AAAA record for api.<cluster_name>.<base_domain>.
    • A DNS A/AAAA record with a wildcard for *.apps.<cluster_name>.<base_domain>.
  • Port 6443 is open for the API URL to allow users outside the firewall to access the cluster by using the oc CLI tool.
  • Port 443 is open for the console to allow users outside the firewall to access the console.
  • A DNS A/AAAA record for each node in the cluster when using User Managed Networking, or the installation will not proceed. DNS A/AAAA records are required for each node in the cluster when using Cluster Managed Networking after installation is complete to connect to the cluster, but installation can proceed without the A/AAAA records when using Cluster Managed Networking.
  • A DNS PTR record for each node in the cluster if you want to boot with the preset hostname when using static IP addressing. Otherwise, the Assisted Installer has an automatic node renaming feature when using static IP addressing that will rename the nodes to their network interface MAC address.
Important
  • DNS A/AAAA record settings at top-level domain registrars can take significant time to update. Ensure the A/AAAA record DNS settings are working before installation to prevent installation delays.
  • For DNS record examples, see Example DNS configuration.

The OpenShift Container Platform cluster’s network must also meet the following requirements:

  • Connectivity between all cluster nodes
  • Connectivity for each node to the internet
  • Access to an NTP server for time synchronization between the cluster nodes

2.3.1.1. Example DNS configuration

This section provides A and PTR record configuration examples that meet the DNS requirements for deploying OpenShift Container Platform using the Assisted Installer. The examples 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.

2.3.1.2. Example DNS A record configuration

The following example is a BIND zone file that shows sample A records for name resolution in a cluster installed using the Assisted Installer.

Example 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	192.168.1.1
smtp.example.com.		IN	A	192.168.1.5
;
helper.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
;
control-plane0.ocp4.example.com.	IN	A	192.168.1.97 4
control-plane1.ocp4.example.com.	IN	A	192.168.1.98
control-plane2.ocp4.example.com.	IN	A	192.168.1.99
;
worker0.ocp4.example.com.	IN	A	192.168.1.11 5
worker1.ocp4.example.com.	IN	A	192.168.1.7
;
;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 worker machines by default.
Note

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 control plane machines.
5
Provides name resolution for the worker machines.

2.3.1.3. Example DNS PTR record configuration

The following example is a BIND zone file that shows sample PTR records for reverse name resolution in a cluster installed using the Assisted Installer.

Example 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
;
97.1.168.192.in-addr.arpa.	IN	PTR	control-plane0.ocp4.example.com. 3
98.1.168.192.in-addr.arpa.	IN	PTR	control-plane1.ocp4.example.com.
99.1.168.192.in-addr.arpa.	IN	PTR	control-plane2.ocp4.example.com.
;
11.1.168.192.in-addr.arpa.	IN	PTR	worker0.ocp4.example.com. 4
7.1.168.192.in-addr.arpa.	IN	PTR	worker1.ocp4.example.com.
;
;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 control plane machines.
4
Provides reverse DNS resolution for the worker machines.
Note

A PTR record is not required for the OpenShift Container Platform application wildcard.

2.3.2. Networking requirements for IBM Z

In IBM Z® environments, advanced networking technologies like Original Storage Architecture (OSA), HiperSockets, and Remote Direct Memory Access (RDMA) over Converged Ethernet (RoCE) require specific configurations that deviate from the standard settings used in Assisted Installer deployments. These overrides are necessary to accommodate their unique requirements and ensure a successful and efficient deployment on IBM Z®.

The following table lists the network devices that are supported for the network configuration override functionality:

Network devicez/VMKVMLPAR ClassicLPAR Dynamic Partition Manager (DPM)

Original Storage Architecture (OSA) virtual switch

Not supported

 — 

Not supported

Not supported

Direct attached OSA

Supported

Only through a Linux bridge

Supported

Not supported

RDMA over Converged Ethernet (RoCE)

Not supported

Only through a Linux bridge

Not supported

Not supported

HiperSockets

Supported

Only through a Linux bridge

Supported

Not supported

Linux bridge

Not supported

Supported

Not supported

Not supported

2.3.2.1. Configuring network overrides in IBM Z

You can specify a static IP address on IBM Z® machines that uses Logical Partition (LPAR) and z/VM. This is specially useful when the network devices do not have a static MAC address assigned to them.

If you have an existing .parm file, edit it to include the following entry: 

ai.ip_cfg_override=1

This parameter allows the file to add the network settings to the CoreOS installer.

Example of the .parm file

rd.neednet=1 cio_ignore=all,!condev
console=ttysclp0
coreos.live.rootfs_url=<coreos_url> 1
ip=<ip>::<gateway>:<netmask>:<hostname>::none nameserver=<dns>
rd.znet=qeth,<network_adaptor_range>,layer2=1
rd.<disk_type>=<adapter> 2
rd.zfcp=<adapter>,<wwpn>,<lun> random.trust_cpu=on 3
zfcp.allow_lun_scan=0
ai.ip_cfg_override=1 4
ignition.firstboot ignition.platform.id=metal
random.trust_cpu=on

1
For the coreos.live.rootfs_url artifact, specify the matching rootfs artifact for the kernel and initramfs that you are booting. Only HTTP and HTTPS protocols are supported.
2
For installations on direct access storage devices (DASD) type disks, use rd. to specify the DASD where Red Hat Enterprise Linux (RHEL) is to be installed. For installations on Fibre Channel Protocol (FCP) disks, use rd.zfcp=<adapter>,<wwpn>,<lun> to specify the FCP disk where RHEL is to be installed.
3
Specify values for adapter, wwpn, and lun as in the following example: rd.zfcp=0.0.8002,0x500507630400d1e3,0x4000404600000000.
4
Specify this parameter when using an OSA network adapter or HiperSockets.
Note

The override parameter overrides the host’s network configuration settings.

2.4. Preflight validations

The Assisted Installer ensures the cluster meets the prerequisites before installation, because it eliminates complex postinstallation troubleshooting, thereby saving significant amounts of time and effort. Before installing software on the nodes, the Assisted Installer conducts the following validations:

  • Ensures network connectivity
  • Ensures sufficient network bandwidth
  • Ensures connectivity to the registry
  • Ensures that any upstream DNS can resolve the required domain name
  • Ensures time synchronization between cluster nodes
  • Verifies that the cluster nodes meet the minimum hardware requirements
  • Validates the installation configuration parameters

If the Assisted Installer does not successfully validate the foregoing requirements, installation will not proceed.

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