Configuration for the size bounds of an instance group,
including its proportional size to other groups.
Optional. Minimum number of instances for this group.
Primary workers - Bounds: [2, max_instances]. Default: 2.
Secondary workers - Bounds: [0, max_instances]. Default: 0.
Required. Maximum number of instances for this group.
Required for primary workers. Note that by default, clusters
will not use secondary workers. Required for secondary
workers if the minimum secondary instances is set.
Primary workers - Bounds: [min_instances, ). Secondary
workers - Bounds: [min_instances, ). Default: 0.
Optional. Weight for the instance group, which is used to
determine the fraction of total workers in the cluster from
this instance group. For example, if primary workers have
weight 2, and secondary workers have weight 1, the cluster
will have approximately 2 primary workers for each secondary
The cluster may not reach the specified balance if
constrained by min/max bounds or other autoscaling settings.
For example, if max_instances for secondary workers is
0, then only primary workers will be added. The cluster can
also be out of balance when created.
If weight is not set on any instance group, the cluster will
default to equal weight for all groups: the cluster will
attempt to maintain an equal number of workers in each group
within the configured size bounds for each group. If weight
is set for one group only, the cluster will default to zero
weight on the unset group. For example if weight is set only
on primary workers, the cluster will use primary workers
only and no secondary workers.