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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 allocate 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

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 if you intend to allow users outside the firewall to access the cluster via the oc CLI tool.
  • Port 443 is open for the console if you intend 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 in order 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 in this chapter.

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

2.4. 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.

2.4.1. 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.

2.4.2. 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.

2.5. 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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