Show server numa topology

Add NUMA into new sub-resource GET /servers/{server_id}/topology API.

Problem description

There is server-related NUMA information that is useful to both end user and Admin but currently there is no available API to retrieve that information.

The APIs GET /servers and GET /servers/{id} can list extra specs which may contain some hints about the guest numa topology but it is not easy to interpret.

Use Cases

  • The admin wants to see the topology (RAM, CPU) without logging in to the guest VM.

  • The admin wants a unified way to get topology information, independent of how the various gest OSes expose it.

  • The admin wants to know the virtual-to-physical mapping for one or more instances for the purpose of debugging, and admin need make sure the NUMA topology is what it’s supposed to be, and is correctly mapped onto Host.

  • The end user could have all of above abilities if admin alows them by change policy rule.

Proposed change

In nova, NUMA topology contains group of related properties, like the amount of memory managed by a NUMA cell, the list of memory page sizes supported on the NUMA cell,the vCPU thread to logical host processor mapping, and the cpu thread policy. This spec proposes an API to present all this NUMA information, including the virtual-to-physical mapping.

This spec proposes a new sub-resource ‘topology’ to servers API:

GET /servers/{server_id}/topology

This API is admin only by default, it could be exposed to users/roles by changing the default policy rule.

API returns each cell’s information belonging to one server, including socket, cpu, thread, mem, page size, cpuset, CPU pinned info, siblings, thread policy, CPU pinning, host NUMA node number.

If there is no NUMA information available, the corresponding key’s value will simply be set to None.


Instead of put these information into GET /servers/{server_id}/topology, there are other 2 options:

  • add NUMA information into existed sub-resource diagnostics: GET /servers/{server_id}/diagnostics returns the NUMA information for one server. As NUMA toplogy does not change for given server, it’s better put under new topology sub-resource.

  • put the NUMA information under GET /servers/{id} and GET /servers/detail. This would negatively affect performance as it needs an additional database query (via the InstanceNUMATopology object’s get_by_instance_uuid method).

Data model impact


REST API impact

API GET /servers/{server_id}/topology will show NUMA information with a new microversion.

The returned information for NUMA topology:

      # overall policy: TOPOLOGY % 'index
                   # Host Numa Node
                   # control by policy TOPOLOGY % 'index:host_info'
                   "host_numa_node": 3,
                   # 0:5 means vcpu 0 pinning to pcpu 5
                   # control by policy TOPOLOGY % 'index:host_info'
                   "cpu_pinning": {0:5, 1:6},
                   "vcpu_set": [0,1,2,3],
                   "siblings": [[0,1],[2,3]],
                   "memory_mb": 1024,
                   "pagesize_kb": 4096,
                   "sockets": 1,
                   "cores": 2,
                   # one core has at least one thread
                   "threads": 2
                ], # nodes

     "cpu_thread_policy": "prefer"


Security impact

  • These information exposed by this API is admin only by default, and fine control policy TOPOLOGY % 'index:host_info' use to keep host only information to admin while this API expose to end user.

  • Add new topology policy, admin only by default:

    TOPOLOGY = 'os_compute_api:servers:topology:%s'
    server_topology_policies = [
            "Show the topology data for a server",
                    'method': 'GET',
                    'path': '/servers/{server_id}/topology'
            # control host numa node and cpu pin information
            TOPOLOGY % 'index:host_info',
            "List all servers with detailed information",
                    'method': 'GET',
                    'path': '/servers/{server_id}/topology'

Notifications impact


Other end user impact

  • python novaclient and python-openstackclient would display numa_topology information.

Performance Impact


Other deployer impact


Developer impact


Upgrade impact




Primary assignee:

Yongli He

Work Items

  • Add new microversion for this change.




  • Add functional api_sample tests.

Documentation Impact

The API document should be changed to introduce this new feature.




Release Name



First Introduced