Chapter 2. Planning your undercloud
2.1. Containerized undercloud
The undercloud is the node that controls the configuration, installation, and management of your final OpenStack Platform environment, which is called the overcloud. The undercloud itself uses OpenStack Platform components in the form of containers to create a toolset called OpenStack Platform director. This means 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 you can use as a toolset for creating and managing your overcloud.
Since both the undercloud and overcloud uses 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 for configuring services and containers. It is useful to have some familiarity with Heat and Ansible to help you troubleshoot issues 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 the 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 no other DHCP services should exist on this network. The director configures the interface for this network.
- The External network that 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 provisioning a large number of nodes in your overcloud environment.
Note the following:
- 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 connected to the Provisioning network during introspection.
- Include at least one permanent IP address for each node connected 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
Prior to installing the undercloud, it is recommended to determine the scale of your environment. Include the following factors when planningyour environment:
- How many nodes 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 overcloud nodes.
- How many simultaneous operations do you want the undercloud 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 undercloud’s total CPU thread count [1]. For example, if your undercloud has a CPU with 16 threads, then the director services spawn 8 workers by default. The director also uses a set of minimum and maximum caps by default:
| Service | Minimum | Maximum |
|---|---|---|
| OpenStack Orchestration (heat) | 4 | 24 |
| All other service | 2 | 12 |
The undercloud has the 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-ansibleplaybook consumes 1 GB resident set size (RSS) per 10 hosts deployed by the undercloud. If the deployed overcloud will use an existing Ceph cluster, or if it will deploy a new Ceph cluster, then provision undercloud RAM accordingly.
-
The
To use a larger number of workers, increase your undercloud’s vCPUs and memory using the following recommendations:
- Minimum: Use 1.5 GB of memory per thread. For example, a machine with 48 threads should have 72 GB of RAM. This provides the minimum coverage for 24 Heat workers and 12 workers for other services.
- Recommended: Use 3 GB of memory per thread. For example, a machine with 48 threads should have 144 GB of RAM. This provides 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:
| Platform | Notes |
|---|---|
| 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. |
Red Hat OpenStack Platform director requires that Red Hat Enterprise Linux 8.2 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_addrparameter 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.
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
LANGenvironment variable is set toen_US.UTF-8on 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. Considerations when running the undercloud with a proxy
If your environment uses a proxy, review these considerations to best understand the different configuration methods of integrating parts of Red Hat OpenStack Platform with a proxy and the limitations of each method.
System-wide proxy configuration
Use this method to configure proxy communication for all network traffic on the undercloud. To configure the proxy settings, edit the /etc/environment file and set the following environment variables:
- http_proxy
- The proxy that you want to use for standard HTTP requests.
- https_proxy
- The proxy that you want to use for HTTPs requests.
- no_proxy
- A comma-separated list of domains that you want to exclude from proxy communications.
The system-wide proxy method has the following limitations:
-
The
no_proxyvariable primarily uses domain names (www.example.com), domain suffixes (example.com), and domains with a wildcard (*.example.com). Most Red Hat OpenStack Platform services interpret IP addresses inno_proxybut certain services, such as container health checks, do not interpret IP addresses in theno_proxyenvironment variable due to limitations with cURL andwget. To use a system-wide proxy with the undercloud, disable container health checks with thecontainer_healthcheck_disabledparameter in theundercloud.conffile during installation.
dnf proxy configuration
Use this method to configure dnf to run all traffic through a proxy. To configure the proxy settings, edit the /etc/dnf/dnf.conf file and set the following parameters:
- proxy
- The URL of the proxy server.
- proxy_username
- The username that you want to use to connect to the proxy server.
- proxy_password
- The password that you want to use to connect to the proxy server.
- proxy_auth_method
- The authentication method used by the proxy server.
For more information about these options, run man dnf.conf.
The dnf proxy method has the following limitations:
-
This method provides proxy support only for
dnf. -
The
dnfproxy method does not include an option to exclude certain hosts from proxy communication.
Red Hat Subscription Manager proxy
Use this method to configure Red Hat Subscription Manager to run all traffic through a proxy. To configure the proxy settings, edit the /etc/rhsm/rhsm.conf file and set the following parameters:
- proxy_hostname
- Host for the proxy.
- proxy_scheme
- The scheme for the proxy when writing out the proxy to repo definitions.
- proxy_port
- The port for the proxy.
- proxy_username
- The username that you want to use to connect to the proxy server.
- proxy_password
- The password to use for connecting to the proxy server.
- no_proxy
- A comma-separated list of hostname suffixes for specific hosts that you want to exclude from proxy communication.
For more information about these options, run man rhsm.conf.
The Red Hat Subscription Manager proxy method has the following limitations:
- This method provides proxy support only for Red Hat Subscription Manager.
- The values for the Red Hat Subscription Manager proxy configuration override any values set for the system-wide environment variables.
Transparent proxy
If your network uses a transparent proxy to manage application layer traffic, you do not need to configure the undercloud itself to interact with the proxy because proxy management occurs automatically. A transparent proxy can help overcome limitations associated with client-based proxy configuration in Red Hat OpenStack Platform.
2.8. Undercloud repositories
Enable the following repositories for the installation and configuration of the undercloud.
Core repositories
The following table lists core repositories for installing the undercloud.
| Name | Repository | Description of Requirement |
|---|---|---|
| Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs) |
| Base operating system repository for x86_64 systems. |
| Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs) |
| Contains Red Hat OpenStack Platform dependencies. |
| Red Hat Enterprise Linux 8 for x86_64 - High Availability (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 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 |
| Tools for managing hosts with Red Hat Satellite 6. |
| Red Hat OpenStack Platform 15 for RHEL 8 (RPMs) |
| Core Red Hat OpenStack Platform repository, which contains packages for Red Hat OpenStack Platform director. |
| Red Hat Fast Datapath for RHEL 8 (RPMS) |
| Provides Open vSwitch (OVS) packages for OpenStack Platform. |
IBM POWER repositories
The following table lists repositories for Openstack Platform on POWER PC architecture. Use these repositories in place of equivalents in the Core repositories.
| Name | Repository | Description of Requirement |
|---|---|---|
| Red Hat Enterprise Linux for IBM Power, little endian - BaseOS (RPMs) |
| Base operating system repository for ppc64le systems. |
| Red Hat Enterprise Linux 8 for IBM Power, little endian - AppStream (RPMs) |
| Contains Red Hat OpenStack Platform dependencies. |
| Red Hat Enterprise Linux 8 for IBM Power, little endian - High Availability (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 Engine for Red Hat Enterprise Linux. Used to provide the latest version of Ansible. |
| Red Hat OpenStack Platform 15 for RHEL 8 (RPMs) |
| Core Red Hat OpenStack Platform repository for ppc64le systems. |
