openstack-helm/doc/source/devref/node-and-label-specific-configurations.rst

Node and label specific configurations

There are situations where we need to define configuration differently for different nodes in the environment. For example, we may require that some nodes have a different vcpu_pin_set or other hardware specific deltas in nova.conf.

To do this, we can specify overrides in the values fed to the chart. Ex:

conf:
  nova:
    DEFAULT:
      vcpu_pin_set: "0-31"
      cpu_allocation_ratio: 3.0
  overrides:
    nova_compute:
      labels:
      - label:
          key: compute-type
          values:
          - "dpdk"
          - "sriov"
        conf:
          nova:
            DEFAULT:
              vcpu_pin_set: "0-15"
      - label:
          key: another-label
          values:
          - "another-value"
        conf:
          nova:
            DEFAULT:
              vcpu_pin_set: "16-31"
      hosts:
      - name: host1.fqdn
        conf:
          nova:
            DEFAULT:
              vcpu_pin_set: "8-15"
      - name: host2.fqdn
        conf:
          nova:
            DEFAULT:
              vcpu_pin_set: "16-23"

Note that only one set of overrides is applied per node, such that:

1. Host overrides supercede label overrides
2. The farther down the list the label appears, the greater precedence it has. e.g., "another-label" overrides will apply to a node containing both labels.

Also note that other non-overridden values are inherited by hosts and labels with overrides. The following shows a set of example hosts and the values fed into the configmap for each:

1. host1.fqdn with labels compute-type: dpdk, sriov and another-label: another-value:

   conf:
     nova:
       DEFAULT:
         vcpu_pin_set: "8-15"
         cpu_allocation_ratio: 3.0

2. host2.fqdn with labels compute-type: dpdk, sriov and another-label: another-value:

   conf:
     nova:
       DEFAULT:
         vcpu_pin_set: "16-23"
         cpu_allocation_ratio: 3.0

3. host3.fqdn with labels compute-type: dpdk, sriov and another-label: another-value:

   conf:
     nova:
       DEFAULT:
         vcpu_pin_set: "16-31"
         cpu_allocation_ratio: 3.0

4. host4.fqdn with labels compute-type: dpdk, sriov:

   conf:
     nova:
       DEFAULT:
         vcpu_pin_set: "0-15"
         cpu_allocation_ratio: 3.0

5. host5.fqdn with no labels:

   conf:
     nova:
       DEFAULT:
         vcpu_pin_set: "0-31"
         cpu_allocation_ratio: 3.0