Chapter 3. Configuring and installing the undercloud

3.1. Configuring the spine leaf provisioning networks

To configure the provisioning networks for your spine leaf infrastructure, edit the undercloud.conf file and set the relevant parameters included in the following procedure.

Procedure

  1. Log in to the undercloud as the stack user.
  2. If you do not already have an undercloud.conf file, copy the sample template file:

    [stack@director ~]$ cp /usr/share/python-tripleoclient/undercloud.conf.sample ~/undercloud.conf
  3. Edit the undercloud.conf file.
  4. Set the following values in the [DEFAULT] section:

    1. Set local_ip to the undercloud IP on leaf0:

      local_ip = 192.168.10.1/24
    2. Set undercloud_public_host to the externally facing IP address of the undercloud:

      undercloud_public_host = 10.1.1.1
    3. Set undercloud_admin_host to the administration IP address of the undercloud. This IP address is usually on leaf0:

      undercloud_admin_host = 192.168.10.2
    4. Set local_interface to the interface to bridge for the local network:

      local_interface = eth1
    5. Set enable_routed_networks to true:

      enable_routed_networks = true
    6. Define your list of subnets using the subnets parameter. Define one subnet for each L2 segment in the routed spine and leaf:

      subnets = leaf0,leaf1,leaf2
    7. Specify the subnet associated with the physical L2 segment local to the undercloud using the local_subnet parameter:

      local_subnet = leaf0
    8. Set the value of undercloud_nameservers.

      undercloud_nameservers = 10.11.5.19,10.11.5.20
      Tip

      You can find the current IP addresses of the DNS servers that are used for the undercloud nameserver by looking in /etc/resolv.conf.

  5. Create a new section for each subnet that you define in the subnets parameter:

    [leaf0]
    cidr = 192.168.10.0/24
    dhcp_start = 192.168.10.10
    dhcp_end = 192.168.10.90
    inspection_iprange = 192.168.10.100,192.168.10.190
    gateway = 192.168.10.1
    masquerade = False
    
    [leaf1]
    cidr = 192.168.11.0/24
    dhcp_start = 192.168.11.10
    dhcp_end = 192.168.11.90
    inspection_iprange = 192.168.11.100,192.168.11.190
    gateway = 192.168.11.1
    masquerade = False
    
    [leaf2]
    cidr = 192.168.12.0/24
    dhcp_start = 192.168.12.10
    dhcp_end = 192.168.12.90
    inspection_iprange = 192.168.12.100,192.168.12.190
    gateway = 192.168.12.1
    masquerade = False
  6. Save the undercloud.conf file.
  7. Run the undercloud installation command:

    [stack@director ~]$ openstack undercloud install

This configuration creates three subnets on the provisioning network or control plane. The overcloud uses each network to provision systems within each respective leaf.

To ensure proper relay of DHCP requests to the undercloud, you might need to configure a DHCP relay.

3.2. Configuring a DHCP relay

The undercloud uses two DHCP servers on the provisioning network:

  • An introspection DHCP server.
  • A provisioning DHCP server.

When you configure a DHCP relay, ensure that you forward DHCP requests to both DHCP servers on the undercloud.

You can use UDP broadcast with devices that support it to relay DHCP requests to the L2 network segment where the undercloud provisioning network is connected. Alternatively, you can use UDP unicast, which relays DHCP requests to specific IP addresses.

Note

Configuration of DHCP relay on specific device types is beyond the scope of this document. As a reference, this document provides a DHCP relay configuration example using the implementation in ISC DHCP software. For more information, see manual page dhcrelay(8).

Broadcast DHCP relay

This method relays DHCP requests using UDP broadcast traffic onto the L2 network segment where the DHCP server or servers reside. All devices on the network segment receive the broadcast traffic. When using UDP broadcast, both DHCP servers on the undercloud receive the relayed DHCP request. Depending on the implementation, you can configure this by specifying either the interface or IP network address:

Interface
Specify an interface that is connected to the L2 network segment where the DHCP requests are relayed.
IP network address
Specify the network address of the IP network where the DHCP requests are relayed.

Unicast DHCP relay

This method relays DHCP requests using UDP unicast traffic to specific DHCP servers. When you use UDP unicast, you must configure the device that provides the DHCP relay to relay DHCP requests to both the IP address that is assigned to the interface used for introspection on the undercloud and the IP address of the network namespace that the OpenStack Networking (neutron) service creates to host the DHCP service for the ctlplane network.

The interface used for introspection is the one defined as inspection_interface in the undercloud.conf file. If you have not set this parameter, the default interface for the undercloud is br-ctlplane.

Note

It is common to use the br-ctlplane interface for introspection. The IP address that you define as the local_ip in the undercloud.conf file is on the br-ctlplane interface.

The IP address allocated to the Neutron DHCP namespace is the first address available in the IP range that you configure for the local_subnet in the undercloud.conf file. The first address in the IP range is the one that you define as dhcp_start in the configuration. For example, 192.168.10.10 is the IP address if you use the following configuration:

[DEFAULT]
local_subnet = leaf0
subnets = leaf0,leaf1,leaf2

[leaf0]
cidr = 192.168.10.0/24
dhcp_start = 192.168.10.10
dhcp_end = 192.168.10.90
inspection_iprange = 192.168.10.100,192.168.10.190
gateway = 192.168.10.1
masquerade = False
Warning

The IP address for the DHCP namespace is automatically allocated. In most cases, this address is the first address in the IP range. To verify that this is the case, run the following commands on the undercloud:

$ openstack port list --device-owner network:dhcp -c "Fixed IP Addresses"
+----------------------------------------------------------------------------+
| Fixed IP Addresses                                                         |
+----------------------------------------------------------------------------+
| ip_address='192.168.10.10', subnet_id='7526fbe3-f52a-4b39-a828-ec59f4ed12b2' |
+----------------------------------------------------------------------------+
$ openstack subnet show 7526fbe3-f52a-4b39-a828-ec59f4ed12b2 -c name
+-------+--------+
| Field | Value  |
+-------+--------+
| name  | leaf0  |
+-------+--------+

Example dhcrelay configuration

In the following example, the dhcrelay command in the dhcp package uses the following configuration:

  • Interfaces to relay incoming DHCP request: eth1, eth2, and eth3.
  • Interface the undercloud DHCP servers on the network segment are connected to: eth0.
  • The DHCP server used for introspection is listening on IP address: 192.168.10.1.
  • The DHCP server used for provisioning is listening on IP address 192.168.10.10.

This results in the following dhcrelay command:

$ sudo dhcrelay -d --no-pid 192.168.10.10 192.168.10.1 \
  -i eth0 -i eth1 -i eth2 -i eth3

Example Cisco IOS routing switch configuration

This example uses the following Cisco IOS configuration to perform the following tasks:

  • Configure a VLAN to use for the provisioning network.
  • Add the IP address of the leaf.
  • Forward UDP and BOOTP requests to the introspection DHCP server that listens on IP address: 192.168.10.1.
  • Forward UDP and BOOTP requests to the provisioning DHCP server that listens on IP address 192.168.10.10.
interface vlan 2
ip address 192.168.24.254 255.255.255.0
ip helper-address 192.168.10.1
ip helper-address 192.168.10.10
!

If you require the ability to automatically discover bare metal nodes without the need to create an instack.json file, you can use auto-discovery to register overcloud nodes. See Automatically discovering bare metal nodes for more information.

3.3. Using the direct deploy interface

In a default undercloud configuration, ironic deploys nodes using the iscsi deploy interface. When using the iscsi deploy interface, the deploy ramdisk publishes the node’s disk as an iSCSI target, and the ironic-conductor service then copies the image to this target.

For a DCN deployment, network latency is often a concern between the undercloud and the distributed compute nodes. Considering the potential for latency, the distributed compute nodes should be configured to use the direct deploy interface in the undercloud.

When using the direct deploy interface, the deploy ramdisk downloads the image over HTTP from the undercloud’s Swift or Ironic conductor service, and copies it to the node’s disk. HTTP is more resilient when dealing with network latency than iSCSI, so using the direct deploy interface provides a more stable node deployment experience for distributed compute nodes.

Procedure

The iSCSI deploy interface is the default deploy interface. However, you can enable the direct deploy interface to download an image from a HTTP location to the target disk.

Note

Your overcloud node memory tmpfs must have at least 8GB of memory.

  1. Create or modify a custom environment file /home/stack/undercloud_custom_env.yaml and specify the IronicDefaultDeployInterface.

    parameter_defaults:
      IronicDefaultDeployInterface: direct
  2. Specify the service that provides the image. By default, the Bare Metal service (ironic) agent on each node obtains the image stored in the Object Storage service (swift) through a HTTP link. If this behavior is desired, not further changes are necessary. Alternatively, ironic can stream this image directly to the node through the ironic-conductor HTTP server if you set the IronicImageDownloadSource to http in the /home/stack/undercloud_custom_env.yaml file:

    parameter_defaults:
      IronicDefaultDeployInterface: direct
      IronicImageDownloadSource: http
  3. Include the custom environment file in the DEFAULT section of the undercloud.conf file:

    custom_env_files = /home/stack/undercloud_custom_env.yaml