OnDemandMinCount

Minimum number of on-demand instances to maintain when using spot instances. This should be set to a value that will guarantee the minimum acceptable service availability. You must set it even if you are using HighAvailability as false, as this will be used to create the minimum on-demand instances.

| Default value | 3 | | Minimum value | 1 |

Use Cases

• Ensuring a baseline of 3 on-demand instances for production workloads while using spot instances for cost savings on additional capacity
• Reducing to 1 in non-HA development Racks that use spot instances to minimize costs
• Increasing above 3 for mission-critical workloads where spot instance interruptions must not impact availability

Additional Information

This parameter is primarily relevant when using spot instances. On-demand instances provide guaranteed availability, while spot instances can be interrupted when AWS needs the capacity back. By setting an appropriate OnDemandMinCount, you ensure that your Rack always has a stable base of instances that cannot be interrupted.

If you are not using spot instances (i.e., SpotInstanceBid is not set), this parameter still defines the minimum on-demand count in the Auto Scaling group.

$ convox rack params set OnDemandMinCount=2

See Also

• SpotInstanceBid
• InstanceCount
• HighAvailability
• NoHaInstanceCount