Chapter 8. Scaling the Overcloud

There might be situations where you need to add or remove nodes after the creation of the Overcloud. For example, you might need to add more Compute nodes to the Overcloud. This situation requires updating the Overcloud.
Use the following table to determine support for scaling each node type:

Table 8.1. Scale Support for Each Node Type

Node Type
Scale Up?
Scale Down?
Notes
Controller
N
N
Compute
Y
Y
Ceph Storage Nodes
Y
N
You must have at least 1 Ceph Storage node from the initial Overcloud creation.
Cinder Storage Nodes
N
N
Swift Storage Nodes
N
N

Important

Make sure to leave at least 10 GB free space before scaling the Overcloud. This free space accommodates image conversion and caching during the node provisioning process.

8.1. Adding Compute or Ceph Storage Nodes

To add more nodes to the director's node pool, create a new JSON file (for example, newnodes.json) containing the new node details to register:
{
  "nodes":[
    {
        "mac":[
            "dd:dd:dd:dd:dd:dd"
        ],
        "cpu":"4",
        "memory":"6144",
        "disk":"40",
        "arch":"x86_64",
        "pm_type":"pxe_ipmitool",
        "pm_user":"admin",
        "pm_password":"p@55w0rd!",
        "pm_addr":"192.0.2.207"
    },
    {
        "mac":[
            "ee:ee:ee:ee:ee:ee"
        ],
        "cpu":"4",
        "memory":"6144",
        "disk":"40",
        "arch":"x86_64",
        "pm_type":"pxe_ipmitool",
        "pm_user":"admin",
        "pm_password":"p@55w0rd!",
        "pm_addr":"192.0.2.208"
    }
  ]
}
See Section 6.2.1, “Registering Nodes for the Advanced Overcloud” for an explanation of these parameters.
Run the following command to register these nodes:
$ openstack baremetal import --json newnodes.json
After registering the new nodes, launch the introspection process for them. Use the following commands for each new node:
$ ironic node-list
$ ironic node-set-maintenance [NODE UUID] true
$ openstack baremetal introspection start [NODE UUID]
$ ironic node-set-maintenance [NODE UUID] false
This detects and benchmarks the hardware properties of the nodes.
After the introspection process completes, tag each new node for its desired role. For example, for a Compute node, use the following command:
$ ironic node-update [NODE UUID] add properties/capabilities='profile:compute,boot_option:local'
Alternatively, you can automatically tag new nodes into desired roles using the Automated Health Check (AHC) Tools. See Section 6.2.3, “Automatically Tagging Nodes with Automated Health Check (AHC) Tools” for more information.
Set the boot images to use during the deployment. Find the UUIDs for the bm-deploy-kernel and bm-deploy-ramdisk images:
$ glance image-list
+--------------------------------------+------------------------+
| ID                                   | Name                   |
+--------------------------------------+------------------------+
| 09b40e3d-0382-4925-a356-3a4b4f36b514 | bm-deploy-kernel       |
| 765a46af-4417-4592-91e5-a300ead3faf6 | bm-deploy-ramdisk      |
| ef793cd0-e65c-456a-a675-63cd57610bd5 | overcloud-full         |
| 9a51a6cb-4670-40de-b64b-b70f4dd44152 | overcloud-full-initrd  |
| 4f7e33f4-d617-47c1-b36f-cbe90f132e5d | overcloud-full-vmlinuz |
+--------------------------------------+------------------------+
Set these UUIDs for the new node's deploy_kernel and deploy_ramdisk settings:
$ ironic node-update [NODE UUID] add driver_info/deploy_kernel='09b40e3d-0382-4925-a356-3a4b4f36b514'
$ ironic node-update [NODE UUID] add driver_info/deploy_ramdisk='765a46af-4417-4592-91e5-a300ead3faf6'
Scaling the Overcloud requires running the openstack overcloud deploy again with the desired number of nodes for a role. For example, to scale to 5 Compute nodes:
$ openstack overcloud deploy --templates --compute-scale 5 [OTHER_OPTIONS]
This updates the entire Overcloud stack. Note that this only updates the stack. It does not delete the Overcloud and replace the stack.

Important

Make sure to include all environment files and options from your initial Overcloud creation. This includes the same scale parameters for non-Compute nodes.