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Preferred Set Up

Preferred Instance Types​

This article introduces Preferred Instance Types, provides a guide on how to use them and explains how they work. Preferred spot instance types let customers set priority tiers on the Elastigroups' configured spot types. Types that are selected as preferred will be prioritized over other types and will be used whenever possible considering availability and cost. In cases that any of the preferred types are not available, Elastigroup will use other types that are selected in the group.

Step 1: Select Allowed Spot Instance Types​

  1. Enter the Elastigroup configuration by editing an existing Elastigroup or creating a new Elastigroup.

  2. Go to the Compute tab and scroll down to Spot Types. (If you are creating a new Elastigroup, you must complete the required information in the General tab before you can enter the Compute tab.)

  3. Mark all the Spot instance types that you allow for the Elastigroup.

  4. Complete the rest of the required information in the Compute tab and click Next.

Step 2: Select your Preferred Instance Types​

  1. In the Predictive Rebalancing tab, scroll down to Instance Availability.

  2. The Preferred Spot Types combo box will now be populated with your allowed spot types. Mark your preferred types in this list.

  3. Complete any additional required information in the configuration and click Update (for a new Elastigroup, click Create).

How Preferred Instance Types Work​

Preferred spot types divide the selected spot instance types into two groups:

  • Tier1: Preferred spot types
  • Tier2: Spot types that were NOT selected as preferred spot types

When scaling, Elastigroup will distribute the instances across different availability zones and instance types based on the configuration you defined to ensure availability. When there aren't sufficient available preferred markets, Elastigroup will distribute a minimal number of instances to non-preferred markets.

Example 1: Group with 12 instances and 4 preferred spot types

Preferred MarketsOther Markets
100%0%
12 instances0 instances

Example 2: Group with 32 instances and 3 preferred spot types

Preferred MarketsOther Markets
75%25%
24 instances8 instances

Preferred Availability Zones​

When you set up an Elastigroup, you choose a region, and according to the Availability Zones (AZs) existing in that region, you choose the AZs that you want to be allowed for instances Spot creates.

In general, it is good practice to simply allow all the AZs existing in that region, as shown below. This maximizes the possibilities for Spot to find spot instances that meet your exact specifications.

However, you may have specific use cases in which it is advantageous to use only certain AZs. For example, you might want to use a reduced number or only a single AZ for the following reasons:

  • You want to reduce network costs by minimizing the number of times you change zones and transfer data from one zone to another.
  • You want to improve application performance by confining all your computing to a minimum geographic area, i.e., to only one AZ where all of your workloads run.

You can configure this in Elastigroup using the Preferred Availability Zones feature. When you define Preferred Availability Zones, Spot will always look in those AZs first when it needs to start up a new spot instance, and it will try to launch all of your instances in those AZs only. If no instances exist in the preferred AZs, Spot will then consider available instances in the other AZs you have allowed.

To set up preferred AZs, follow the steps below.

Step 1: Select Allowed Availability Zones​

  1. Enter the Elastigroup configuration by editing an existing Elastigroup or creating a new Elastigroup.

  2. In the Compute tab, go to Availability Zones. (If you are creating a new Elastigroup, you must complete the required information in the General tab before you can enter the Compute tab.)

  3. Mark all the AZs that you allow for the Elastigroup. For each AZ, choose one or more subnets.

    tip

    To diversify the spot markets available for the Elastigroup, it is highly recommended to choose all the AZs listed for the region.

Step 2: Select your Preferred Availability Zones​

  1. Go to the Predictive Rebalancing tab and scroll down to Availability Zones.

  2. The Preferred Availability Zones combo box will now be populated with the allowed AZs you marked in the Compute tab. Mark your preferred AZs in this list.

  3. Complete any additional required information in the configuration and click Update (for a new Elastigroup, click Create).