PCD Designing highly scalable, available, and reliable cloud-native applications Practice Test 7 — 15 Questions

Question 1

A company is designing a microservices application. They want to ensure that if one service fails, it does not cascade to other services. Which pattern should they implement?

Accepted Answer

Circuit Breaker. The Circuit Breaker pattern is the correct choice because it prevents cascading failures by monitoring service calls and opening the circuit when failures exceed a threshold, allowing the system to fail fast and avoid resource exhaustion. This pattern directly addresses the requirement to isolate failures between microservices, ensuring that a failure in one service does not propagate to others.

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Auto-scaling

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Retry with exponential backoff

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Load shedding

Question 2

A company runs a global e-commerce platform on GKE. They need to serve users with low latency from multiple regions. Which load balancing solution should they use?

Accepted Answer

Global external HTTP(S) Load Balancer. A global external HTTP(S) Load Balancer is the correct choice because it provides a single anycast IP address that routes traffic from users worldwide to the nearest GKE backend, minimizing latency. It supports cross-regional failover and integrates with Cloud CDN for caching static content, making it ideal for a global e-commerce platform. Regional load balancers cannot serve traffic across multiple regions with a single IP, which is required for global low-latency access.

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Regional external HTTP(S) Load Balancer

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Internal TCP/UDP Load Balancer

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SSL Proxy Load Balancer

Question 3

A developer is building a Cloud Pub/Sub-based event-driven system. They need to ensure that messages are processed at least once, and they want to handle processing failures. What should they do?

Accepted Answer

Use push subscriptions with a dead-letter topic. Option D is correct because using push subscriptions with a dead-letter topic ensures at-least-once delivery and provides a mechanism to handle processing failures. When a push subscription fails to deliver a message (e.g., due to a downstream error), Pub/Sub automatically retries delivery. After exhausting the maximum delivery attempts (default 5), the message is forwarded to a dead-letter topic, where it can be analyzed or reprocessed without losing the message. This guarantees that every message is either processed successfully or stored for manual intervention, satisfying the at-least-once requirement.

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Use pull subscriptions with auto-acknowledgment

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Configure max delivery attempts on the subscription

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Use Cloud Tasks instead of Pub/Sub

Question 4

An organization runs a critical application on Compute Engine with a regional managed instance group. They want to achieve 99.99% availability. Which architecture should they use?

Accepted Answer

Regional MIG with instances in three zones. To achieve 99.99% availability, the architecture must tolerate both a zonal failure and a single instance failure. A regional managed instance group (MIG) with instances in three zones ensures that even if one zone becomes unavailable, the remaining two zones can still serve traffic, meeting the 99.99% uptime target. Three zones provide the necessary redundancy because a two-zone regional MIG can only survive a single zone failure but not a simultaneous instance failure in the remaining zone, whereas three zones allow for a rolling update or failure of one zone while still maintaining quorum.

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Regional MIG with instances in two zones

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Single zone MIG with multiple instances

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Multi-region deployment with global load balancer

Question 5

A company uses Cloud Spanner for a financial application. They need to ensure strong global consistency but also minimize latency for writes. What schema design should they use?

Accepted Answer

Use parent-child table relationships with interleaved tables. Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, reducing cross-node coordination for strongly consistent reads and writes. This minimizes write latency by ensuring that related data is stored together, avoiding distributed transaction overhead for operations that span parent-child relationships.

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Use secondary indexes

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Use commit timestamps

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Use a single table with interleaved indexes

Question 6

A developer is designing a chat application using Cloud Firestore. They need to ensure that updates to messages are propagated to all clients in real-time. Which feature should they use?

Accepted Answer

Real-time listeners. Real-time listeners (onSnapshot) in Cloud Firestore allow clients to subscribe to document or query changes, receiving updates immediately when data is modified. This ensures all connected clients see message updates in real-time without polling, which is essential for a chat application.

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Firestore indexes

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Security rules

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Offline persistence

Question 7

Refer to the exhibit. A company configured an HPA for their deployment. They notice that the HPA is not scaling based on the 'packets-per-second' metric. What is the most likely reason?

Accepted Answer

The metric is not available in the cluster.. The 'packets-per-second' metric is a custom metric. If it is not registered in the cluster's metrics server (e.g., via custom metrics adapter), the HPA will not be able to collect it. The metric name and target type are correct. The scaleTargetRef matches the deployment. Therefore, the metric being unavailable is the most likely issue.

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The metric name 'packets-per-second' is incorrect.

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The target type should be 'Value' instead of 'AverageValue'.

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The HPA is using the wrong scaleTargetRef.

Question 8

A company is designing a cloud-native application on Google Kubernetes Engine. They want to ensure high availability and scalability for their microservices. Which two best practices should they follow?

Accepted Answer

Use horizontal pod autoscaling based on custom metrics.. Horizontal Pod Autoscaling (HPA) based on custom metrics allows the application to automatically scale the number of pod replicas in response to application-specific signals (e.g., requests per second, queue depth) rather than just CPU/memory. This ensures that each microservice can handle varying load efficiently, maintaining high availability and scalability without over-provisioning.

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Use a single cluster per region.

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Use a single replica for each service to reduce cost.

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Use stateful sets for all services.

Question 9

A developer is building an event-driven system using Cloud Pub/Sub. They need to ensure reliable message delivery and processing. Which three practices should they follow?

Accepted Answer

Use pull subscriptions with synchronous acknowledgment.. Pull subscriptions with synchronous acknowledgment (option B) ensure that a message is not acknowledged until the subscriber has successfully processed it. This prevents premature acknowledgment and message loss, because Cloud Pub/Sub will redeliver the message if the acknowledgment deadline expires without a synchronous ack. This is a core pattern for reliable processing.

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Set a minimum number of delivery attempts.

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Use message ordering.

Question 10

A company is using Cloud Run for a stateless API. They want to ensure that the service can handle sudden traffic spikes. Which two features should they configure?

Accepted Answer

Enable container concurrency.. Option A is correct because enabling container concurrency allows a single Cloud Run container instance to handle multiple requests simultaneously, up to the configured concurrency limit (default 80, max 1000). This improves throughput and resource utilization during traffic spikes without requiring additional instances. Option D is correct because setting max instances to a high value ensures the service can scale out to handle sudden load by creating more container instances, up to the configured maximum, preventing cold starts and request queuing.

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Use Cloud Load Balancing.

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Enable CPU always on allocation.

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Set min instances to zero to save cost.

Question 11

A company runs a microservices application on Google Kubernetes Engine. They use Cloud SQL for persistent data. Recently, during a traffic spike, the application experienced increased latency and some requests failed with timeout errors. The team observed that the Cloud SQL CPU utilization spiked to 100%, and the GKE pods had high memory usage. They are using a standard Cloud SQL tier (db-n1-standard-2). Which course of action would best improve the application's performance and reliability?

Accepted Answer

Implement caching with Memorystore for frequently accessed data.. The correct answer is D because the primary bottleneck is the Cloud SQL CPU spiking to 100% under heavy read traffic. Implementing Memorystore (Redis) caching offloads repeated read queries from the database, reducing CPU load and query latency. This directly addresses the root cause—database CPU exhaustion—without requiring a larger database instance or adding replicas that would still be limited by the same CPU.

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Upgrade Cloud SQL to a higher tier with more CPU.

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Increase the number of replicas in GKE to reduce load per pod.

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Add read replicas to Cloud SQL.

Question 12

A company uses Cloud Run for a serverless application that processes user uploads. Users report that sometimes the first request after a period of inactivity takes very long (cold start). The application is stateless. They want to minimize cold start latency while keeping costs low. The application is deployed with default settings: min instances = 0, max instances = 100, CPU always off, and a container image of 1GB. What should they do to reduce cold start latency?

Accepted Answer

Set min instances to 1 to keep a warm instance.. Setting min instances to 1 ensures that at least one instance is always warm and ready to serve requests, eliminating the cold start for the first request after a period of inactivity. Since the application is stateless and the default min instances is 0, Cloud Run scales down to zero, causing a cold start on the next request. By keeping one instance warm, you minimize latency without significantly increasing cost, as you only pay for the single idle instance.

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Increase container memory from the default to reduce startup time.

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Use a larger container image to include more dependencies.

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Enable CPU always on allocation.

Question 13

A company is running a global application on Cloud Spanner. They notice high write latency on a specific table because a frequently updated row is being accessed by many clients simultaneously. Which design pattern should they implement to distribute writes across multiple nodes and reduce contention?

Accepted Answer

Add a hash suffix to the primary key of the hot row to split it into multiple rows.. Option C is correct because adding a hash suffix to the primary key of the hot row splits the single heavily contended row into multiple logical rows, each with a different primary key. This distributes the write load across multiple Cloud Spanner splits and nodes, reducing lock contention and write latency. Cloud Spanner uses a distributed, synchronous replication architecture where a single row is managed by a single split; splitting the hot row into multiple rows allows parallel writes to different splits.

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Increase the number of nodes in the Cloud Spanner instance.

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Use interleaved tables to co-locate related data.

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Migrate the table to Cloud Bigtable which handles hotspots better.

Question 14

A company wants to design a highly available web application that serves users globally. They plan to use Cloud Load Balancing. Which two design choices should they make to ensure high availability and low latency? (Choose two.)

Accepted Answer

Enable Cloud CDN to cache static content closer to users.. Enabling Cloud CDN caches static content at Google's global edge locations, reducing latency by serving content from a point of presence (PoP) close to the user. This offloads requests from backend instances, improving overall availability and performance for global users.

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Use a single-zone backend instance group for simplicity.

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Use Cloud Armor to filter malicious traffic.

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Deploy separate regional load balancers in each region and use DNS-based routing.

Question 15

A company is deploying a global microservices application on Cloud Run. They need to design for high availability, scalability, and low latency. Which three practices should they implement? (Choose three.)

Accepted Answer

Enable Cloud CDN for caching static assets.. Option B is correct because Cloud CDN caches static assets at Google's global edge locations, reducing latency for users worldwide and offloading requests from Cloud Run. This improves performance for static content like images, CSS, and JavaScript, which is essential for a global microservices application requiring low latency.

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Use Cloud Scheduler to trigger services periodically.

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Set a limit on the number of Cloud Run containers per revision to control costs.