Compute questions in the AZ-305 exam are often scenario-driven — you’ll need to recommend the right compute option based on business requirements, not just technical features. Many services sound similar, and exam writers love to test your ability to distinguish between them.
This capsule summarizes common mistakes, quick decision rules, and exam strategies.
Common Pitfalls
1. VM vs App Service vs Functions
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VM = full control, legacy workloads, OS-level dependencies.
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App Service = managed PaaS for web apps/APIs.
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Functions = event-driven, short-lived tasks.
Exam Trap: If the workload is a web app and you see both VM and App Service, the right answer is usually App Service, unless OS control is explicitly required.
2. VM Scale Sets vs AKS
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VMSS = scale out identical VMs.
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AKS = orchestrated containerized workloads.
Exam Trap: If microservices or container orchestration is mentioned → AKS, not VMSS.
3. AKS vs App Service Containers
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AKS = for many services running at scale with orchestration.
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App Service Containers = for a single containerized app.
Exam Trap: If exam says “50 microservices, need scaling and CI/CD” → AKS.
4. Service Bus vs Event Grid vs Event Hubs
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Service Bus = enterprise messaging, guaranteed delivery, ordering.
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Event Grid = lightweight event routing.
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Event Hubs = massive event ingestion.
Exam Trap: If the scenario mentions financial transactions, the answer is Service Bus, not Event Grid.
5. App Configuration vs Key Vault
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App Config = non-sensitive settings + feature flags.
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Key Vault = secrets, keys, certificates.
Exam Trap: If passwords, keys, or connection strings are mentioned → Key Vault.
6. Redis vs SQL
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Redis = caching layer for performance.
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SQL = persistent storage.
Exam Trap: If the scenario says “reduce DB load by caching session state”, answer = Redis, not SQL DB.
Exam Strategies
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Look for Key Phrases
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“Legacy app requiring OS-level access” → VM.
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“Web app, minimal management” → App Service.
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“Event-driven processing, pay-per-use” → Functions.
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“Microservices with orchestration” → AKS.
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“Asynchronous reliable messaging” → Service Bus.
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“Feature flags” → App Configuration.
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“Global caching of frequent queries” → Redis.
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Think Business Requirements First
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Cost optimization → Spot VMs, Functions, App Service.
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Compliance/regulatory → ASE (App Service Environment), Key Vault.
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High availability → Availability Zones, Scale Sets.
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Don’t Over-Engineer
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If simple PaaS service works, don’t choose VMs or AKS unless explicitly needed.
Quick Recall Table
| Requirement | Best Solution |
|---|---|
| Full OS control, legacy workloads | Virtual Machine |
| Scalable web apps & APIs | App Service |
| Event-driven, short tasks | Azure Functions |
| Container orchestration | AKS |
| Single container app | App Service with container |
| Scale out identical VMs | VM Scale Sets |
| API gateway, versioning, auth | API Management |
| Reliable enterprise messaging | Service Bus |
| Telemetry ingestion | Event Hubs |
| Event-driven workflows | Event Grid |
| High-speed caching | Redis |
| Feature flags | App Configuration |
| Secrets/keys/certificates | Key Vault |
Exam Tips
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Expect scenario questions like:
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“Company wants to modernize legacy app with minimal refactoring.” → Managed Instance or VM.
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“Company requires auto-scaling web app.” → App Service.
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“Microservices architecture with containers and CI/CD.” → AKS.
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Watch for keywords like “event-driven”, “global scale”, “session state”, “API gateway”, “feature flags” — they directly map to services.
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Avoid retired or legacy services (e.g., Cloud Services) if they show up as distractors.
What to Expect in the Exam
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Direct Q: “Which Azure service is best for caching frequent queries?” → Redis.
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Scenario Q: “Company requires low-cost compute that runs only when triggered.” → Functions.
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Scenario Q: “Which service provides API versioning and rate limiting?” → API Management.
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Trick Q: “VM Scale Sets are required to run microservices orchestration.” → False (AKS is correct).