Google ACE Practice Question: Deploy a new version of their application with…

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Create a new MIG, then update the load balancer's backend service

  Why it's wrong here

  While creating a new MIG and updating the load balancer backend is a valid zero-downtime strategy, it doesn't directly address the requirement of *deploying a new version of their application*. This method is suitable for replacing an entire MIG with a new one, perhaps with different instance configurations, but not for a rolling update of the application code on existing instances. It's tempting because it achieves zero downtime through a full replacement, but it doesn't facilitate a phased application version rollout.

• ✗

  Delete the current MIG and create a new one with the updated template

  Why it's wrong here

  Deleting the current MIG and creating a new one with the updated template is a disruptive replacement strategy: once the old MIG is deleted, all its instances are terminated immediately, and the new MIG's instances take time to boot, pass health checks, and register with the load balancer. During that gap, the backend service has zero healthy instances, so users receive 502/503 errors. Unlike a rolling update, this approach does not preserve capacity during the transition, and any load balancer draining or connection draining must be manually configured to avoid dropped traffic.

• ✗

  Update the instance template and restart all instances

  Why it's wrong here

  Updating an instance template does not alter the configuration of existing instances; instances only see the new template when they are recreated. Restarting all instances at once, whether by a rolling restart or a global restart, removes the entire serving capacity simultaneously, causing a full outage even if you use a health check. A proper way to apply a template change is to replace instances incrementally, not restart them all in one step, because a simultaneous restart offers no window for the new version to become healthy while the old version still serves traffic.

• ✓

  Perform a rolling update using a new instance template, with a health check

  Why this is correct

  A rolling update with a new instance template and a health check is the correct way to deploy a new application version without downtime: the MIG progressively creates new instances from the updated template, waits for each to pass the configured health check, and then terminates the old instances. You can control the rollout speed with parameters like maxSurge and maxUnavailable, which ensure that a certain number of old instances remain serving at all times. The health check acts as the gate — if the new version fails health checks, the rollout pauses and old instances stay in service, allowing you to roll back without a full outage. This method directly targets the application version on existing instances, unlike a full MIG replacement, because it updates the instance group in place through the MIG's native update mechanism.

Go deeper

Related to this question