Enable fallback mode in a scaling configuration to improve the scale-out success rate

Console

1. Log on to the Auto Scaling console.

2. In the navigation pane on the left, click Scaling Groups. In the top navigation bar, select a region.

3. On the Scaling Groups page, find the target scaling group and click its name.

4. On the Scaling Configuration tab, perform one of the following operations:

   • To create a new scaling configuration, click Create Scaling Configuration.

   • To modify an existing scaling configuration, find the configuration and click Modify in the Actions column.

5. In the Image and Instance section, set Instance Configuration Mode to Specify Instance Type, and then select your desired instance types.

6. Above the list of selected instance types, click the Alternative Mode button.

   The Set Alternative Specification Range dialog box appears.

7. In the Set Alternative Specification Range dialog box, configure the fallback scope as needed. The following table describes the parameters.

   Parameter	Description
   Maximum Price	The maximum hourly price for fallback instance types. The system displays the Highest unit price of selected types for reference. Set the limit slightly above the current maximum (up to 10% higher) to expand the fallback pool.
   Instance Type	Turn on the Allow instance types from other generations switch to include same-sized instance types from other generations. For example, if the primary type is ecs.c7.large, this allows ecs.c6.large or ecs.c8.large as alternatives.
   Vpc_vSwitch	Turn on the Allow supplemental vSwitches in other zones switch. When all selected zones are out of stock, the scaling group automatically creates a vSwitch in another zone and adds it to the scaling group.
   vSwitch CIDR Blocks	Required only when Allow adding vSwitches from other zones is enabled. Specify the IPv4 CIDR block for automatically created vSwitches. Requirements: The mask length must be 16 to 29 bits. The CIDR block must fall within the VPC CIDR block. The CIDR block cannot match the destination CIDR block of a route entry in the VPC, but can be a subset. The CIDR block cannot be 100.64.0.0/10 or any of its subnets.

8. Click OK to save the settings.

   On the scaling configuration page, a preview of Alternative Specifications and Alternative Zone appears below the instance type list, showing the instance types and zones that may be used based on your scope settings.

9. After configuring other settings, click Create or Modify to complete the scaling configuration.

10. (Optional) Enable the scaling configuration.

CLI/API

When you call the CreateScalingConfiguration or ModifyScalingConfiguration operation through the CLI or an SDK, use the following parameters to configure fallback mode:

Console

• Scaling configuration list: Scaling configurations with fallback mode enabled display an Alternative Mode tag for quick identification.

• Scaling configuration details: Click a scaling configuration ID to open its details, which show the complete fallback mode configuration:

  • Whether fallback mode is enabled.

  • The price limit.

  • Whether instance types from other generations are allowed.

  • Whether supplemental vSwitches in other availability zones are allowed.

  • The vSwitch CIDR blocks, if configured.

CLI/API

Call the DescribeScalingConfigurations operation through the CLI or an SDK. The response includes the following fallback mode fields:

Console

1. Log on to the Auto Scaling console.

2. In the navigation pane on the left, click Scaling Groups. In the top navigation bar, select a region.

3. On the Scaling Groups page, find the target scaling group and click its name.

4. On the Scaling Configuration tab, find the configuration and click Modify in the Actions column.

5. Click Edit Candidate Scope. In the Set Alternative Specification Range dialog box, configure the scope as needed. The following table describes each parameter.

   Parameter	Description
   Maximum Price	The maximum hourly price for fallback instance types. The system displays the Highest unit price of selected types for reference. Set the limit slightly above the current maximum (up to 10% higher) to expand the fallback pool.
   Instance Type	Turn on the Allow instance types from other generations switch to include same-sized instance types from other generations. For example, if the primary type is ecs.c7.large, this allows ecs.c6.large or ecs.c8.large as alternatives.
   Vpc_vSwitch	Turn on the Allow supplemental vSwitches in other zones switch. When all selected zones are out of stock, the scaling group automatically creates a vSwitch in another zone and adds it to the scaling group.
   vSwitch CIDR Blocks	Required only when Allow adding vSwitches from other zones is enabled. Specify the IPv4 CIDR block for automatically created vSwitches. Requirements: The mask length must be 16 to 29 bits. The CIDR block must fall within the VPC CIDR block. The CIDR block cannot match the destination CIDR block of a route entry in the VPC, but can be a subset. The CIDR block cannot be 100.64.0.0/10 or any of its subnets.

6. Click Modify to save your changes to the scaling configuration.

CLI/API

Call the ModifyScalingConfiguration operation through the CLI or an SDK to configure fallback mode with the following parameters:

Console

1. Log on to the Auto Scaling console.

2. In the navigation pane on the left, click Scaling Groups. In the top navigation bar, select a region.

3. On the Scaling Groups page, find the target scaling group and click its name.

4. On the Scaling Configuration tab, find the configuration and click Modify in the Actions column.

5. To the right of the instance type selection, turn off the Alternative Mode switch.

6. Click Modify to save your changes to the scaling configuration.

CLI/API

Call the ModifyScalingConfiguration API operation via CLI or SDK and set InstanceTypeCandidateOptions.Enabled to false.