mediumMultiple ChoiceObjective-mapped
Google ACE Practice Question: A team needs to roll out a configuration change…
A team needs to roll out a configuration change to a MIG (Managed Instance Group) — updating the instance template to set a new environment variable. They want to validate the change on 1 VM before rolling it out to all 20 VMs. Which MIG update type supports this?
⚠ Common exam trap
Google Cloud often tests the distinction between 'canary' and 'opportunistic' updates, where candidates mistakenly think opportunistic allows manual selection of a single VM to update, but it only applies changes during natural instance replacement.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Canary update — update 1 VM to the new template, verify, then roll out to all
A canary update in a Managed Instance Group (MIG) allows you to specify a target size (e.g., 1 VM) to update to the new instance template first. After validating the change on that single VM, you can then promote the canary to roll out the new template to the remaining 19 VMs. This matches the requirement to test on 1 VM before full rollout.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Canary update — update 1 VM to the new template, verify, then roll out to all
Why this is correct
Canary update is the MIG feature specifically designed for staged rollout: you define a target size (e.g., 1 out of 20) for the new instance template, so the MIG creates exactly one VM running the new environment variable while the other 19 continue on the old template. After validating that the canary VM passes health checks and behaves as expected, you can promote the new template across the entire group by increasing the target size to all instances. This provides a controlled, incremental rollout with the MIG managing versioning and rollback automatically.
- ✗
Opportunistic update — the new template applies only when VMs are naturally replaced
Why it's wrong here
Opportunistic update only applies the new instance template when VMs are naturally replaced, such as through autoscaling scale-out, autohealing, or manual deletion. This mode does not proactively renew existing instances on a schedule, so the 20 running VMs would keep the old environment variable indefinitely, with no guarantee that even one VM gets replaced in a timely manner. It is an update mode for low-risk rollouts, not a canary strategy, because you cannot force one specific VM to update now for verification.
- ✗
Recreate update — terminate all 20 VMs and recreate with the new template simultaneously
Why it's wrong here
Recreate update terminates all 20 VMs at the same time and rebuilds them from the new template, causing a complete outage and eliminating any opportunity to test the change on a single VM first. While MIG's recreate strategy does support full parallel replacement, it is explicitly not a canary mechanism because every instance is destroyed and recreated simultaneously. If the new environment variable contains a bug, you lose all 20 old VMs before you have any signal — the opposite of staged validation.
- ✗
Snapshot the existing VMs and restore 1 with the new environment variable to test
Why it's wrong here
Snapshots capture the disk state of a VM, not the instance template configuration or environment variables baked into the instance metadata. Restoring a VM from a snapshot only rolls back its disk contents, and there is no mechanism to 'restore with a new environment variable' from that snapshot. MIG updates are driven by instance template versions and rollout strategies, not disk snapshots, so this approach would never validate the new environment variable on a true MIG-managed instance or exercise the group's health checks and load balancing.
Go deeper
Related to this question
Learn chapter
Instance Templates and Managed Instance Groups
Key term
Instance template
An instance template is a reusable configuration blueprint that defines the virtual machine settings, such as machine type, boot disk image, and network, for creating identical VM instances in Google Cloud Platform.
Key term
Managed instance group
A managed instance group is a collection of identical virtual machine instances that are automatically managed as a single unit to ensure high availability and scalability.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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