You have developed a non-critical update to your application that is running in a managed instance group, and have created a new instance template with the update that you want to release. To prevent any possible impact to the application, you don't want to update any running instances. You want any new instances that are created by the managed instance group to contain the new update. What should you do?

The correct answer is to start a new rolling update and select the Opportunistic update mode. This mode ensures that existing instances are not proactively updated. Instead, the new instance template is applied only when instances are created, restarted, or recreated for other reasons (e.g., autohealing, scaling). This aligns with the requirement to prevent any impact to the running application and only apply the update to new instances. A rolling restart operation would restart all instances, causing downtime. A rolling replace operation would actively replace all instances, also causing downtime and not meeting the requirement to avoid updating running instances. A rolling update with Proactive update mode would immediately begin updating existing instances, which is precisely what the question states you want to avoid.