PDE Designing Data Processing Systems Practice Question
A healthcare company is designing a system to ingest HL7 messages from multiple hospitals into Google Cloud. The messages must be processed in near real-time to extract patient vitals and trigger alerts if thresholds are exceeded. The system must guarantee that no messages are lost and that processing is exactly-once. Which combination of Google Cloud services should they use?
⚠ Common exam trap
The trap here is assuming that any message processing service can achieve exactly-once semantics without considering the specific guarantees of the processing engine.
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
✓
Cloud Pub/Sub with a pull subscription and Cloud Dataflow with exactly-once processing
Cloud Pub/Sub with a pull subscription ensures reliable message delivery, and Cloud Dataflow supports exactly-once processing for streaming pipelines. Together, they provide a managed solution that guarantees no message loss and exactly-once semantics. Dataflow can process HL7 messages in near real-time, extract vitals, and trigger alerts. This combination is the most robust and operationally efficient way to meet the strict processing guarantees required by the healthcare scenario.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Cloud Pub/Sub with a pull subscription and a custom application on Compute Engine that uses the Pub/Sub client library
Why it's wrong here
A custom application on Compute Engine can achieve exactly-once processing if it implements deduplication and transactional writes, but this requires significant development effort and careful handling of failures. It does not inherently provide exactly-once semantics; the developer must build that logic. This increases operational overhead and risk of errors. While it can process messages in near real-time, it does not offer the managed exactly-once guarantee that Dataflow provides.
- ✓
Cloud Pub/Sub with a pull subscription and Cloud Dataflow with exactly-once processing
Why this is correct
Cloud Pub/Sub provides reliable, scalable message ingestion with at-least-once delivery. When combined with Cloud Dataflow, which supports exactly-once processing semantics for streaming pipelines, this ensures that each message is processed exactly once. Dataflow can handle near real-time processing, extract vitals, and trigger alerts. This combination meets the requirements for no message loss and exactly-once processing in a near real-time system.
- ✗
Cloud Pub/Sub with a push subscription to a Cloud Function that writes to Cloud Firestore
Why it's wrong here
Cloud Functions can process messages in near real-time, but they do not natively provide exactly-once processing semantics. Push subscriptions can deliver messages multiple times, and without idempotent processing or deduplication, duplicates could occur. Additionally, Cloud Functions have execution time limits and may not be suitable for complex stream processing. This approach does not guarantee exactly-once processing and may lead to duplicate alerts or missed messages.
- ✗
Cloud Pub/Sub with a push subscription to Cloud Run, which then publishes to a second Pub/Sub topic for Dataflow
Why it's wrong here
Introducing Cloud Run and a second Pub/Sub topic adds complexity and potential points of failure. Cloud Run does not provide exactly-once processing, and the double-hop through Pub/Sub could still result in duplicates. While Dataflow could process the second topic with exactly-once, the overall pipeline does not guarantee exactly-once end-to-end because the initial processing in Cloud Run may duplicate or lose messages. This design does not meet the requirement for exactly-once processing.
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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
This PDE 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 PDE exam.