Google PCA Design and plan a cloud solution architecture Practice Question
A logistics company runs a latency-sensitive inventory service on Compute Engine in us-central1. The service writes to a Cloud SQL for MySQL instance and reads from a Memorystore for Redis cache. The architect must design for a zone failure in us-central1 with minimal data loss and automatic failover, without changing the application's connection strings. Which design should the architect choose?
⚠ Common exam trap
The trap here is assuming that read replicas or a multi-zone application tier alone provide high availability, when the database and cache tiers must also have automatic failover.
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
✓
Deploy the service in a managed instance group across three zones, use a Cloud SQL for MySQL regional instance with a primary and standby, and configure Memorystore for Redis in Standard Tier with automatic failover.
Spreading the service across zones with a regional managed instance group, pairing it with a Cloud SQL regional instance that has a standby in another zone, and using Memorystore Standard Tier with automatic failover together address zone failure at every tier. Each component exposes stable endpoints, so the application keeps its existing connection strings.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Deploy the service in a managed instance group across three zones, use a Cloud SQL for MySQL regional instance with a primary and standby, and configure Memorystore for Redis in Standard Tier with automatic failover.
Why this is correct
A regional managed instance group spreads VMs across zones so a single zone failure does not take down the service. A Cloud SQL regional instance maintains a standby in another zone and fails over automatically with minimal data loss. Memorystore for Redis Standard Tier provides a replica and automatic failover. The application connects through stable endpoints, so no connection string changes are needed.
- ✗
Deploy the service in a multi-region managed instance group, use Cloud Spanner instead of Cloud SQL, and use Memorystore for Redis in Basic Tier.
Why it's wrong here
Replacing Cloud SQL with Cloud Spanner changes the database engine and requires application changes, which conflicts with the no-connection-string-change constraint. A multi-region managed instance group is broader than the stated single-region zone-failure requirement and raises cost. Memorystore Basic Tier still lacks automatic failover, leaving the cache as a single point of failure.
- ✗
Deploy the service across two zones, use a Cloud SQL for MySQL regional instance, and run a self-managed Redis cluster on Compute Engine with Sentinel.
Why it's wrong here
The Cloud SQL regional instance is appropriate, but self-managing Redis with Sentinel adds operational burden and requires the application to understand Sentinel failover, which may change how clients connect. Memorystore Standard Tier provides managed failover without that complexity. The self-managed option also introduces a second component the team must patch and monitor.
- ✗
Deploy the service in a zonal managed instance group, use a Cloud SQL for MySQL zonal instance, and enable Memorystore for Redis Basic Tier with read replicas.
Why it's wrong here
A zonal managed instance group and a zonal Cloud SQL instance both live in one zone, so a zone failure takes down the service and the database together. Memorystore Basic Tier does not provide automatic failover. Read replicas improve read scaling but do not deliver automatic promotion or the availability guarantees required here.
Go deeper
Related to this question
Learn chapter
Data Migration and Transfer Services
Key term
Latency
Latency is the time delay between a request being sent over a network and the response being received, often measured in milliseconds.
Key term
Instance group
An instance group is a collection of virtual machine instances that are managed as a single unit for scaling, load balancing, and lifecycle management in cloud computing.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Google Cloud exam blueprint
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