Chapter 2. Planning your undercloud

2.1. Containerized undercloud

The undercloud is the node that controls the configuration, installation, and management of your final Red Hat OpenStack Platform (RHOSP) environment, which is called the overcloud. The undercloud itself uses OpenStack Platform components in the form of containers to create a toolset called director. This means that the undercloud pulls a set of container images from a registry source, generates configuration for the containers, and runs each OpenStack Platform service as a container. As a result, the undercloud provides a containerized set of services that you can use as a toolset to create and manage your overcloud.

Since both the undercloud and overcloud use containers, both use the same architecture to pull, configure, and run containers. This architecture is based on the OpenStack Orchestration service (heat) for provisioning nodes and uses Ansible to configure services and containers. It is useful to have some familiarity with heat and Ansible to help you troubleshoot issues that you might encounter.

2.2. Preparing your undercloud networking

The undercloud requires access to two main networks:

  • The Provisioning or Control Plane network, which is the network that director uses to provision your nodes and access them over SSH when executing Ansible configuration. This network also enables SSH access from the undercloud to overcloud nodes. The undercloud contains DHCP services for introspection and provisioning other nodes on this network, which means that no other DHCP services should exist on this network. The director configures the interface for this network.
  • The External network, which enables access to OpenStack Platform repositories, container image sources, and other servers such as DNS servers or NTP servers. Use this network for standard access the undercloud from your workstation. You must manually configure an interface on the undercloud to access the external network.

The undercloud requires a minimum of 2 x 1 Gbps Network Interface Cards: one for the Provisioning or Control Plane network and one for the External network. However, it is recommended to use a 10 Gbps interface for Provisioning network traffic, especially if you want to provision a large number of nodes in your overcloud environment.

Note:

  • Do not use the same Provisioning or Control Plane NIC as the one that you use to access the director machine from your workstation. The director installation creates a bridge by using the Provisioning NIC, which drops any remote connections. Use the External NIC for remote connections to the director system.
  • The Provisioning network requires an IP range that fits your environment size. Use the following guidelines to determine the total number of IP addresses to include in this range:

    • Include at least one temporary IP address for each node that connects to the Provisioning network during introspection.
    • Include at least one permanent IP address for each node that connects to the Provisioning network during deployment.
    • Include an extra IP address for the virtual IP of the overcloud high availability cluster on the Provisioning network.
    • Include additional IP addresses within this range for scaling the environment.

2.3. Determining environment scale

Before you install the undercloud, determine the scale of your environment. Include the following factors when you plan your environment:

How many nodes do you want to deploy in your overcloud?
The undercloud manages each node within an overcloud. Provisioning overcloud nodes consumes resources on the undercloud. You must provide your undercloud with enough resources to adequately provision and control all of your overcloud nodes.
How many simultaneous operations do you want the undercloud to perform?
Most OpenStack services on the undercloud use a set of workers. Each worker performs an operation specific to that service. Multiple workers provide simultaneous operations. The default number of workers on the undercloud is determined by halving the total CPU thread count on the undercloud [1]. For example, if your undercloud has a CPU with 16 threads, then the director services spawn 8 workers by default. Director also uses a set of minimum and maximum caps by default:
ServiceMinimumMaximum

OpenStack Orchestration (heat)

4

24

All other service

2

12

The undercloud has the following minimum CPU and memory requirements:

  • An 8-thread 64-bit x86 processor with support for the Intel 64 or AMD64 CPU extensions. This provides 4 workers for each undercloud service.
  • A minimum of 24 GB of RAM.

    • The ceph-ansible playbook consumes 1 GB resident set size (RSS) for every 10 hosts that the undercloud deploys. If you want to use a new or existing Ceph cluster in your deployment, you must provision the undercloud RAM accordingly.

To use a larger number of workers, increase the vCPUs and memory of your undercloud using the following recommendations:

  • Minimum: Use 1.5 GB of memory for each thread. For example, a machine with 48 threads requires 72 GB of RAM to provide the minimum coverage for 24 heat workers and 12 workers for other services.
  • Recommended: Use 3 GB of memory for each thread. For example, a machine with 48 threads requires 144 GB of RAM to provide the recommended coverage for 24 heat workers and 12 workers for other services.

2.4. Undercloud disk sizing

The recommended minimum undercloud disk size is 100 GB of available disk space on the root disk:

  • 20 GB for container images
  • 10 GB to accommodate QCOW2 image conversion and caching during the node provisioning process
  • 70 GB+ for general usage, logging, metrics, and growth

2.5. Virtualization support

Red Hat only supports a virtualized undercloud on the following platforms:

PlatformNotes

Kernel-based Virtual Machine (KVM)

Hosted by Red Hat Enterprise Linux 8, as listed on certified hypervisors.

Red Hat Virtualization

Hosted by Red Hat Virtualization 4.x, as listed on certified hypervisors.

Microsoft Hyper-V

Hosted by versions of Hyper-V as listed on the Red Hat Customer Portal Certification Catalogue.

VMware ESX and ESXi

Hosted by versions of ESX and ESXi as listed on the Red Hat Customer Portal Certification Catalogue.

Important

Red Hat OpenStack Platform director requires that the latest version of Red Hat Enterprise Linux 8 is installed as the host operating system. This means your virtualization platform must also support the underlying Red Hat Enterprise Linux version.

Virtual Machine Requirements

Resource requirements for a virtual undercloud are similar to those of a bare metal undercloud. You should consider the various tuning options when provisioning such as network model, guest CPU capabilities, storage backend, storage format, and caching mode.

Network Considerations

Note the following network considerations for your virtualized undercloud:

Power Management
The undercloud VM requires access to the overcloud nodes' power management devices. This is the IP address set for the pm_addr parameter when registering nodes.
Provisioning network
The NIC used for the provisioning (ctlplane) network requires the ability to broadcast and serve DHCP requests to the NICs of the overcloud’s bare metal nodes. As a recommendation, create a bridge that connects the VM’s NIC to the same network as the bare metal NICs.
Note

A common problem occurs when the hypervisor technology blocks the undercloud from transmitting traffic from an unknown address. - If using Red Hat Enterprise Virtualization, disable anti-mac-spoofing to prevent this. - If using VMware ESX or ESXi, allow forged transmits to prevent this. You must power off and on the director VM after you apply these settings. Rebooting the VM is not sufficient.

2.6. Character encoding configuration

Red Hat OpenStack Platform has special character encoding requirements as part of the locale settings:

  • Use UTF-8 encoding on all nodes. Ensure the LANG environment variable is set to en_US.UTF-8 on all nodes.
  • Avoid using non-ASCII characters if you use Red Hat Ansible Tower to automate the creation of Red Hat OpenStack Platform resources.

2.7. Undercloud repositories

Red Hat OpenStack Platform 16.0 runs on Red Hat Enterprise Linux 8.1. Before enabling repositories, lock the director to a version with the subscription-manager release command:

$ sudo subscription-manager release --set=8.1

Enable the following repositories for the installation and configuration of the undercloud.

Core repositories

The following table lists core repositories for installing the undercloud.

NameRepositoryDescription of requirement

Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs) Extended Update Support (EUS)

rhel-8-for-x86_64-baseos-eus-rpms

Base operating system repository for x86_64 systems.

Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs) Extended Update Support (EUS)

rhel-8-for-x86_64-appstream-eus-rpms

Contains Red Hat OpenStack Platform dependencies.

Red Hat Enterprise Linux 8 for x86_64 - High Availability (RPMs) Extended Update Support (EUS)

rhel-8-for-x86_64-highavailability-eus-rpms

High availability tools for Red Hat Enterprise Linux. Used for Controller node high availability.

Red Hat Ansible Engine 2.8 for RHEL 8 x86_64 (RPMs)

ansible-2.8-for-rhel-8-x86_64-rpms

Ansible Engine for Red Hat Enterprise Linux. Used to provide the latest version of Ansible.

Red Hat Satellite Tools for RHEL 8 Server RPMs x86_64

satellite-tools-6.5-for-rhel-8-x86_64-rpms

Tools for managing hosts with Red Hat Satellite 6.

Red Hat OpenStack Platform 16.0 for RHEL 8 (RPMs)

openstack-16-for-rhel-8-x86_64-rpms

Core Red Hat OpenStack Platform repository, which contains packages for Red Hat OpenStack Platform director.

Red Hat Fast Datapath for RHEL 8 (RPMS)

fast-datapath-for-rhel-8-x86_64-rpms

Provides Open vSwitch (OVS) packages for OpenStack Platform.

IBM POWER repositories

The following table contains a list of repositories for Red Hat Openstack Platform on POWER PC architecture. Use these repositories in place of equivalents in the Core repositories.

NameRepositoryDescription of requirement

Red Hat Enterprise Linux for IBM Power, little endian - BaseOS (RPMs)

rhel-8-for-ppc64le-baseos-rpms

Base operating system repository for ppc64le systems.

Red Hat Enterprise Linux 8 for IBM Power, little endian - AppStream (RPMs)

rhel-8-for-ppc64le-appstream-rpms

Contains Red Hat OpenStack Platform dependencies.

Red Hat Enterprise Linux 8 for IBM Power, little endian - High Availability (RPMs)

rhel-8-for-ppc64le-highavailability-rpms

High availability tools for Red Hat Enterprise Linux. Used for Controller node high availability.

Red Hat Ansible Engine 2.8 for RHEL 8 IBM Power, little endian (RPMs)

ansible-2.8-for-rhel-8-ppc64le-rpms

Ansible Engine for Red Hat Enterprise Linux. Provides the latest version of Ansible.

Red Hat OpenStack Platform 16.0 for RHEL 8 (RPMs)

openstack-16-for-rhel-8-ppc64le-rpms

Core Red Hat OpenStack Platform repository for ppc64le systems.



[1] In this instance, thread count refers to the number of CPU cores multiplied by the hyper-threading value