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Google ACE Practice Question: A DevOps team deploys a MIG (Managed Instance…
A DevOps team deploys a MIG (Managed Instance Group) with autohealing configured. The health check probes `/health` on port 8080 with a 30-second initial delay. After deployment, new VMs are failing the health check and being immediately recreated — causing a restart loop. What is the most likely cause?
⚠ Common exam trap
Google Cloud often tests the distinction between health check path errors (which cause persistent failure) and initial delay misconfiguration (which causes a restart loop), trapping candidates who focus on the path mismatch rather than the timing issue.
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
✓
The initial delay is too short — the application hasn't finished starting before the health check probes begin
The 30-second initial delay is too short for the application to complete its startup sequence. When the health check begins probing before the application is ready, it immediately fails, causing the MIG autohealing mechanism to treat the VM as unhealthy and recreate it, leading to a restart loop. The initial delay must be set to a value that exceeds the application's typical startup time.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The health check HTTP path `/health` doesn't exist — the application uses `/healthz`
Why it's wrong here
A mismatched HTTP path would cause persistent probes to fail with 404, marking every instance unhealthy at all times, not just immediately after creation. The scenario's pattern of new VMs failing in rapid succession points to a startup-window problem: the app hasn't begun listening on the port before the first probe arrives. Correcting `/health` to `/healthz` is a real fix, but it would not explain the timing-specific restart loop described.
- ✓
The initial delay is too short — the application hasn't finished starting before the health check probes begin
Why this is correct
The health check's `initialDelaySec` defines how long the MIG waits after an instance boots before sending the first probe, giving the application time to initialize. If the app takes longer to start than the configured delay, the first probe appears while the port is still closed, the instance is marked unhealthy, and autohealing immediately terminates it — causing an endless recreate/restart loop. Raising `initialDelaySec` (for example to 60–90 seconds for a slow-starting JVM or Node process) breaks the loop by allowing the app to listen before being probed.
- ✗
Autohealing is incompatible with autoscaling — they cannot be used together
Why it's wrong here
Autohealing and autoscaling address orthogonal concerns: autohealing keeps instances in a healthy state by recreating VMs that fail health checks, while autoscaling adds or removes instances based on utilization metrics. They are designed to work together — for example, autohealing can replace a corrupt instance even as autoscaling adjusts the fleet size. There is no inherent compatibility constraint, so this option misdiagnoses the restart loop as a configuration conflict.
- ✗
The MIG does not support HTTP health checks — TCP checks must be used instead
Why it's wrong here
Managed instance groups fully support HTTP, HTTPS, TCP, and HTTP/2 health checks, so the premise of the statement is factually wrong. TCP checks only verify that a port is open, whereas HTTP checks validate an application-level response, which is exactly why the MIG is using an HTTP probe. Since HTTP health checks are a documented, first-class MIG feature, this cannot be the reason the instances are crash-looping.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ACE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ACE exam.