Minor changes to instance pool docs (#1581)

Author: iandexter

docs/resources/instance_pool.md

@@ -40,7 +40,7 @@ The following arguments are supported:
 
 * `instance_pool_name` - (Required) (String) The name of the instance pool. This is required for create and edit operations. It must be unique, non-empty, and less than 100 characters.
 * `min_idle_instances` - (Optional) (Integer) The minimum number of idle instances maintained by the pool. This is in addition to any instances in use by active clusters.
-* `max_capacity` - (Optional) (Integer) The maximum number of instances the pool can contain, including both idle instances and ones in use by clusters. Once the maximum capacity is reached, you cannot create new clusters from the pool and existing clusters cannot autoscale up until some instances are made idle in the pool via [cluster](cluster.md) termination or down-scaling.
+* `max_capacity` - (Optional) (Integer) The maximum number of instances the pool can contain, including both idle instances and ones in use by clusters. Once the maximum capacity is reached, you cannot create new clusters from the pool and existing clusters cannot autoscale up until some instances are made idle in the pool via [cluster](cluster.md) termination or down-scaling. There is no default limit, but as a [best practice](https://docs.databricks.com/clusters/instance-pools/pool-best-practices.html#configure-pools-to-control-cost), this should be set based on anticipated usage.
 * `idle_instance_autotermination_minutes` - (Required) (Integer) The number of minutes that idle instances in excess of the min_idle_instances are maintained by the pool before being terminated. If not specified, excess idle instances are terminated automatically after a default timeout period. If specified, the time must be between 0 and 10000 minutes. If you specify 0, excess idle instances are removed as soon as possible.
 * `node_type_id` - (Required) (String) The node type for the instances in the pool. All clusters attached to the pool inherit this node type and the pool’s idle instances are allocated based on this type. You can retrieve a list of available node types by using the [List Node Types API](https://docs.databricks.com/dev-tools/api/latest/clusters.html#clusterclusterservicelistnodetypes) call.
 * `custom_tags` - (Optional) (Map) Additional tags for instance pool resources. Databricks tags all pool resources (e.g. AWS & Azure instances and Disk volumes). *Databricks allows at most 43 custom tags.*
@@ -51,7 +51,7 @@ The following arguments are supported:
 
 The following options are [available](https://docs.databricks.com/dev-tools/api/latest/instance-pools.html#clusterinstancepoolawsattributes):
 
-* `zone_id` - (Required) (String) Identifier for the availability zone/datacenter in which the instance pool resides. This string is of the form like `"us-west-2a"`. The provided availability zone must be in the same region as the Databricks deployment. For example, `"us-west-2a"` is not a valid zone ID if the Databricks deployment resides in the `"us-east-1"` region. This is an optional field. If not specified, a default zone is used. You can find the list of available zones as well as the default value by using the [List Zones API](https://docs.databricks.com/dev-tools/api/latest/clusters.html#clusterclusterservicelistavailablezones).
+* `zone_id` - (Optional) (String) Identifier for the availability zone/datacenter in which the instance pool resides. This string is of the form like `"us-west-2a"`. The provided availability zone must be in the same region as the Databricks deployment. For example, `"us-west-2a"` is not a valid zone ID if the Databricks deployment resides in the `"us-east-1"` region. If not specified, a default zone is used. You can find the list of available zones as well as the default value by using the [List Zones API](https://docs.databricks.com/dev-tools/api/latest/clusters.html#clusterclusterservicelistavailablezones).
 * `spot_bid_price_percent` - (Optional) (Integer) The max price for AWS spot instances, as a percentage of the corresponding instance type’s on-demand price. For example, if this field is set to 50, and the instance pool needs a new i3.xlarge spot instance, then the max price is half of the price of on-demand i3.xlarge instances. Similarly, if this field is set to 200, the max price is twice the price of on-demand i3.xlarge instances. If not specified, the *default value is 100*. When spot instances are requested for this instance pool, only spot instances whose max price percentage matches this field are considered. *For safety, this field cannot be greater than 10000.*
 * `availability` - (Optional) (String) Availability type used for all instances in the pool. Only `ON_DEMAND` and `SPOT` are supported.