Start an instance refresh

Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.

Select the check box next to your Auto Scaling group.

A split pane opens up at the bottom of the Auto Scaling groups page.

On the Instance refresh tab, in Active instance refresh, choose Start instance refresh.

For Availability settings, do the following:

1. For Instance replacement method:

   • If you haven't set an instance maintenance policy on the Auto Scaling group, the default setting for Instance replacement method is Terminate and launch. This is the legacy default behavior for an instance refresh.

   • If you set an instance maintenance policy on the Auto Scaling group, it provides default values for Instance replacement method. To override the instance maintenance policy, choose Override. Overriding only applies to the current instance refresh. The next time you start an instance refresh, these values are reset to the instance maintenance policy defaults.

   The following procedure explains how to update the instance replacement method.

   1. Choose one of the following instance replacement methods:

      • Launch before terminating: A new instance must be provisioned first before an existing instance can be terminated. This is a good choice for applications that favor availability over cost savings.

      • Terminate and launch: New instances are provisioned at the same time your existing instances are terminated. This is a good choice for applications that favor cost savings over availability. It's also a good choice for applications that should not launch more capacity than is currently available.

      • Custom behavior: This option lets you set up a custom minimum and maximum range for the amount of capacity that you want available when replacing instances. This can help you achieve the right balance between cost and availability.

   2. For Set healthy percentage, enter values for one or both of the following fields. The enable fields vary depending on the option you choose for Instance replacement method.

      • Min: Sets the minimum healthy percentage that's required to proceed with the instance refresh.

      • Max: Sets the maximum healthy percentage that's possible during the instance refresh.

   3. Expand the View estimated temporary capacity during replacements based on current group size section to confirm how the values for Min and Max apply to your group. The exact values used depend on the desired capacity value, which will change if the group scales.

   4. Expand the Set fallback behavior for invalid replacement sizes section, and then choose whether to Violate max healthy percentage in order to prioritize availability, or Violate min healthy percentage.

      Keeping the default Violate min healthy percentage option is not recommended for very small groups. If there is only one instance in the Auto Scaling group, starting an instance refresh can result in an outage.

      This step configures fallback behavior if you are using an Auto Scaling group that doesn't have an instance maintenance policy yet. This option isn't available and doesn't appear when your group has an instance maintenance policy. This option is also only available for the Terminate and launch replacement method. Other replacement methods will violate the maximum healthy percentage in order to prioritize availability.

2. For Instance warmup, enter the number of seconds from when a new instance's state changes to InService to when it finishes initializing. Amazon EC2 Auto Scaling waits this amount of time before moving on to replace the next instance.

   While warming up, a newly launched instance is also not counted toward the aggregated instance metrics of the Auto Scaling group (such as CPUUtilization, NetworkIn, and NetworkOut). If you added scaling policies to the Auto Scaling group, the scaling activities run in parallel. If you set a long interval for the instance refresh warmup period, it takes more time for newly launched instances to show up in the metrics. Therefore, an adequate warmup period keeps Amazon EC2 Auto Scaling from scaling on stale metric data.

   If you have already correctly defined a default instance warmup for the Auto Scaling group, then you don't need to change the instance warmup. However, if you want to override the default, you can set a value for this option. For more information about setting the default instance warmup, see Set the default instance warmup for an Auto Scaling group.

For Refresh settings, do the following:

1. (Optional) For Checkpoints, choose Enable checkpoints to replace instances using an incremental or phased approach to an instance refresh. This provides additional time for verification between sets of replacements. If you choose not to enable checkpoints, the instances are replaced in one nearly continuous operation.

   If you enable checkpoints, see Enable checkpoints (console) for additional steps.

2. Enable or turn off Skip matching:

   • To skip replacing instances that already match your launch template, keep the Enable skip matching check box selected.

   • If you turn off skip matching by clearing this check box, all instances can be replaced.

   When you enable skip matching, you can set a new launch template or a new version of the launch template instead of using the existing one. Do this in the Desired configuration section of the Start instance refresh page.

   Note

   To use the skip matching feature to update an Auto Scaling group that currently uses a launch configuration, you must select a launch template in Desired configuration. Skip matching with a launch configuration is not supported.

3. For Standby instances, choose Ignore, Terminate, or Wait. This determines what happens if instances are found in Standby state. For more information, see Temporarily remove instances from your Auto Scaling group.

   If you choose Wait, you must take additional steps to return these instances to service. If you don't, the instance refresh replaces all InService instances and waits for one hour. Then, if any Standby instances remain, the instance refresh fails. To prevent this situation, choose to Ignore or Terminate these instances instead.

4. For Scale-in protected instances, choose Ignore, Replace, or Wait. This determines what happens if scale-in protected instances are found. For more information, see Use instance scale-in protection.

   If you choose Wait, you must take additional steps to remove scale-in protection from these instances. If you don't, the instance refresh replaces all unprotected instances and waits one hour. Then, if any scale-in protected instances remain, the instance refresh fails. To prevent this situation, choose to Ignore or Replace these instances instead.

(Optional) For CloudWatch alarm, choose Enable CloudWatch alarms, and then choose one or more alarms. CloudWatch alarms can be used to identify any issues and fail the operation if an alarm goes into the ALARM state. For more information, see Start an instance refresh with auto rollback.

(Optional) Expand the Desired configuration section to specify updates that you want to make to your Auto Scaling group.

For this step, you can choose to use JSON or YAML syntax to edit parameter values instead of making selections in the console interface. To do so, choose Use code editor instead of Use console interface. The following procedure explains how to make selections using the console interface.

1. For Update launch template:

   • If you haven't created a new launch template or a new launch template version for your Auto Scaling group, don't select this check box.

   • If you created a new launch template or a new launch template version, select this check box. When you select this option, Amazon EC2 Auto Scaling shows you the current launch template and current launch template version. It also lists any other available versions. Choose the launch template and then choose the version.

     After you choose a version, you can see the version information. This is the version of the launch template that will be used when replacing instances as part of an instance refresh. If the instance refresh succeeds, this version of the launch template will also be used whenever new instances launch, such as when the group scales.

2. For Choose a set of instance types and purchase options to override the instance type in the launch template:

   • Don't select this check box if you want to use the instance type and purchase option you specified in your launch template.

   • Select this check box if you want to override the instance type in the launch template or run Spot Instances. You can either manually add each instance type or choose a primary instance type and recommendation option that retrieves any additional matching instance types for you. If you plan to launch Spot Instances, we recommend adding a few different instance types. This way, Amazon EC2 Auto Scaling can launch another instance type if there is insufficient instance capacity in your chosen Availability Zones. For more information, see Auto Scaling groups with multiple instance types and purchase options.

     Warning

     Don't use Spot Instances with applications that can't handle a Spot Instance interruption. Interruptions can occur if the Amazon EC2 Spot service needs to reclaim capacity.

   If you select this check box, make sure that the launch template doesn't already request Spot Instances. You can't use a launch template that requests Spot Instances to create an Auto Scaling group that uses multiple instance types and launches Spot and On-Demand Instances.

   Note

   To configure these options on an Auto Scaling group that currently uses a launch configuration, you must select a launch template in Update launch template. Overriding the instance type in your launch configuration is not supported.

(Optional) For Rollback settings, choose Enable auto rollback to automatically roll back the instance refresh if it fails.

This setting can only be enabled when the Auto Scaling group meets the prerequisites for using rollbacks.

For more information, see Undo changes with a rollback.

Review all of your selections to confirm that everything is set up correctly.

At this point, it's a good idea to verify that the differences between the current and proposed changes won't affect your application in unexpected or unwanted ways. To confirm that your instance type is compatible with your launch template, see Instance type compatibility.

When you are satisfied with your instance refresh selections, choose Start instance refresh.

Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.

Select the check box next to your Auto Scaling group.

A split pane opens up at the bottom of the Auto Scaling groups page.

On the Instance refresh tab, in Active instance refresh, choose Start instance refresh.

For Availability settings, do the following:

1. For Instance replacement method:

   • If you haven't set an instance maintenance policy on the Auto Scaling group, the default setting for Instance replacement method is Terminate and launch. This is the legacy default behavior for an instance refresh.

   • If you set an instance maintenance policy on the Auto Scaling group, it provides default values for Instance replacement method. To override the instance maintenance policy, choose Override. Overriding only applies to the current instance refresh. The next time you start an instance refresh, these values are reset to the instance maintenance policy defaults.

   The following procedure explains how to update the instance replacement method.

   1. Choose one of the following instance replacement methods:

      • Launch before terminating: A new instance must be provisioned first before an existing instance can be terminated. This is a good choice for applications that favor availability over cost savings.

      • Terminate and launch: New instances are provisioned at the same time your existing instances are terminated. This is a good choice for applications that favor cost savings over availability. It's also a good choice for applications that should not launch more capacity than is currently available.

      • Custom behavior: This option lets you set up a custom minimum and maximum range for the amount of capacity that you want available when replacing instances. This can help you achieve the right balance between cost and availability.

   2. For Set healthy percentage, enter values for one or both of the following fields. The enable fields vary depending on the option you choose for Instance replacement method.

      • Min: Sets the minimum healthy percentage that's required to proceed with the instance refresh.

      • Max: Sets the maximum healthy percentage that's possible during the instance refresh.

   3. Expand the View estimated temporary capacity during replacements based on current group size section to confirm how the values for Min and Max apply to your group. The exact values used depend on the desired capacity value, which will change if the group scales.

   4. Expand the Set fallback behavior for invalid replacement sizes section, and then choose whether to Violate max healthy percentage in order to prioritize availability, or Violate min healthy percentage.

      Keeping the default Violate min healthy percentage option is not recommended for very small groups. If there is only one instance in the Auto Scaling group, starting an instance refresh can result in an outage.

      This step configures fallback behavior if you are using an Auto Scaling group that doesn't have an instance maintenance policy yet. This option isn't available and doesn't appear when your group has an instance maintenance policy. This option is also only available for the Terminate and launch replacement method. Other replacement methods will violate the maximum healthy percentage in order to prioritize availability.

2. For Instance warmup, enter the number of seconds from when a new instance's state changes to InService to when it finishes initializing. Amazon EC2 Auto Scaling waits this amount of time before moving on to replace the next instance.

   While warming up, a newly launched instance is also not counted toward the aggregated instance metrics of the Auto Scaling group (such as CPUUtilization, NetworkIn, and NetworkOut). If you added scaling policies to the Auto Scaling group, the scaling activities run in parallel. If you set a long interval for the instance refresh warmup period, it takes more time for newly launched instances to show up in the metrics. Therefore, an adequate warmup period keeps Amazon EC2 Auto Scaling from scaling on stale metric data.

   If you have already correctly defined a default instance warmup for the Auto Scaling group, then you don't need to change the instance warmup. However, if you want to override the default, you can set a value for this option. For more information about setting the default instance warmup, see Set the default instance warmup for an Auto Scaling group.

For Refresh settings, do the following:

1. (Optional) For Checkpoints, choose Enable checkpoints to replace instances using an incremental or phased approach to an instance refresh. This provides additional time for verification between sets of replacements. If you choose not to enable checkpoints, the instances are replaced in one nearly continuous operation.

   If you enable checkpoints, see Enable checkpoints (console) for additional steps.

2. Enable or turn off Skip matching:

   • To skip replacing instances that already match your launch template and any instance type overrides, keep the Enable skip matching check box selected.

   • If you choose to turn off skip matching by clearing this check box, all instances can be replaced.

   When you enable skip matching, you can set a new launch template or a new version of the launch template instead of using the existing one. Do this in the Desired configuration section of the Start instance refresh page. You can also update your instance type overrides in Desired configuration.

3. For Standby instances, choose Ignore, Terminate, or Wait. This determines what happens if instances are found in Standby state. For more information, see Temporarily remove instances from your Auto Scaling group.

   If you choose Wait, you must take additional steps to return these instances to service. If you don't, the instance refresh replaces all InService instances and waits one hour. Then, if any Standby instances remain, the instance refresh fails. To prevent this situation, choose to Ignore or Terminate these instances instead.

4. For Scale-in protected instances, choose Ignore, Replace, or Wait. This determines what happens if scale-in protected instances are found. For more information, see Use instance scale-in protection.

   If you choose Wait, you must take additional steps to remove scale-in protection from these instances. If you don't, the instance refresh replaces all unprotected instances and waits one hour. Then, if any scale-in protected instances remain, the instance refresh fails. To prevent this situation, choose to Ignore or Replace these instances instead.

(Optional) For CloudWatch alarm, choose Enable CloudWatch alarms, and then choose one or more alarms. CloudWatch alarms can be used to identify any issues and fail the operation if an alarm goes into the ALARM state. For more information, see Start an instance refresh with auto rollback.

In the Desired configuration section, do the following.

For this step, you can choose to use JSON or YAML syntax to edit parameter values instead of making selections in the console interface. To do so, choose Use code editor instead of Use console interface. The following procedure explains how to make selections using the console interface.

1. For Update launch template:

   • If you haven't created a new launch template or a new launch template version for your Auto Scaling group, don't select this check box.

   • If you created a new launch template or a new launch template version, select this check box. When you select this option, Amazon EC2 Auto Scaling shows you the current launch template and current launch template version. It also lists any other available versions. Choose the launch template and then choose the version.

     After you choose a version, you can see the version information. This is the version of the launch template that will be used when replacing instances as part of an instance refresh. If the instance refresh succeeds, this version of the launch template will also be used whenever new instances launch, such as when the group scales.

2. For Use these settings to override the instance type and purchase option defined in the launch template:

   By default, this check box is selected. Amazon EC2 Auto Scaling populates each parameter with the value that's currently set in the mixed instances policy for the Auto Scaling group. Only update values for the parameters that you want to change. For guidance on these settings, see Auto Scaling groups with multiple instance types and purchase options.

   Warning

   We recommend that you do not clear this check box. Only clear it if you want to stop using a mixed instances policy. After the instance refresh succeeds, Amazon EC2 Auto Scaling updates your group to match the Desired configuration. If it no longer includes a mixed instances policy, Amazon EC2 Auto Scaling gradually terminates any Spot Instances that are currently running and replaces them with On-Demand Instances. Or, if your launch template requests Spot Instances, then Amazon EC2 Auto Scaling gradually terminates any On-Demand Instances that are currently running and replaces them with Spot Instances.

(Optional) For Rollback settings, choose Enable auto rollback to automatically roll back the instance refresh if it fails for any reason.

This setting can only be enabled when the Auto Scaling group meets the prerequisites for using rollbacks.

For more information, see Undo changes with a rollback.

Review all of your selections to confirm that everything is set up correctly.

At this point, it's a good idea to verify that the differences between the current and proposed changes won't affect your application in unexpected or unwanted ways. To confirm that your instance type is compatible with your launch template, see Instance type compatibility.

When you are satisfied with your instance refresh selections, choose Start instance refresh.