AZ-204 Develop Azure compute solutions Practice Question
You are building a serverless application using Azure Functions. The function processes large CSV files uploaded to Azure Blob Storage. Each file can be up to 100 MB. The function must parse the file and insert each row into a SQL database. You need to minimize cold start latency and ensure the function can handle the processing within the default timeout. What should you do?
⚠ Common exam trap
Many candidates assume the Premium plan with pre-warmed instances is the only or best way to address cold starts, overlooking that a Dedicated App Service plan with Always On provides a stronger guarantee of cold start elimination and a sufficient default timeout (30 minutes, same as Premium), often at a lower cost for predictable, continuous workloads.
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
✓
Use a dedicated App Service plan with Always On enabled.
A Dedicated App Service plan with Always On enabled eliminates cold starts by keeping the function host loaded continuously, and it provides a default timeout of 30 minutes (configurable up to 230 minutes), which is sufficient for processing 100 MB CSV files. The Consumption plan has a default timeout of 5 minutes (max 10 minutes), which may not be enough for large file processing, and it suffers from cold starts. The Premium plan reduces cold starts with pre-warmed instances but is not necessary when a Dedicated plan with Always On is more cost-effective and meets the requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use the Premium plan with pre-warmed instances.
Why it's wrong here
The Azure Functions Premium plan effectively mitigates cold starts by providing pre-warmed instances and VNET integration capabilities. However, it is a significantly more expensive hosting option compared to a dedicated App Service plan, especially if the primary requirement is simply to avoid cold starts and ensure consistent availability for a non-bursty workload. For scenarios where cost optimization is a factor and the workload doesn't demand the advanced networking features or extreme elasticity of Premium, a dedicated App Service plan offers a more balanced solution.
- ✓
Use a dedicated App Service plan with Always On enabled.
Why this is correct
A dedicated App Service plan provides consistent, allocated resources for your function app, eliminating the variability inherent in consumption-based hosting. Enabling "Always On" ensures that the function host process remains active and responsive, completely preventing cold starts and guaranteeing immediate execution for incoming requests. This plan also supports significantly longer execution timeouts (up to 30 minutes by default, configurable to an hour), making it ideal for tasks requiring sustained processing without interruption.
- ✗
Use Durable Functions to split processing into smaller chunks.
Why it's wrong here
Durable Functions are designed for orchestrating complex, stateful workflows and long-running operations, not for simply optimizing a single file parsing task. Introducing Durable Functions would add unnecessary architectural complexity and overhead, as the problem statement implies a single, potentially long-running, but not inherently distributed or stateful, processing job. The core issue of cold starts or execution time for a monolithic task is not addressed by splitting it into smaller, orchestrated sub-tasks if the orchestrator itself still faces similar hosting challenges.
- ✗
Use the Consumption plan and increase the function timeout to 10 minutes.
Why it's wrong here
While increasing the timeout to 10 minutes is possible for the Consumption plan, it does not address the fundamental issue of cold starts. The Consumption plan scales to zero when idle, meaning the first request after a period of inactivity will still incur a cold start delay as the function host needs to be initialized. This directly impacts initial latency and predictability, making it unsuitable for applications requiring consistently low latency and immediate response times, even if the overall execution time is sufficient.
Quick reference
Azure Blob Storage Tier Comparison
| Tier | Storage Cost | Retrieval Cost | Latency | Use Case |
|---|---|---|---|---|
| Hot | Highest | Lowest | Immediate | Active data, frequent reads |
| Cool | Lower | Higher | Immediate | Data accessed < once / month |
| Cold | Lower still | Higher | Immediate | Data accessed < once / quarter |
| Archive | Lowest | Highest + rehydration delay | Hours | Long-term compliance retention |
Go deeper
Related to this question
Learn chapter
Azure Functions Development
Key term
Azure Functions Bindings
Azure Functions Bindings are declarative connections that link your serverless function code to Azure services or external resources, handling input and output data automatically without writing extra networking or authentication code.
Key term
Azure App Service Plans
An Azure App Service Plan defines the compute resources, pricing tier, scaling capabilities, and region for one or more web apps, API apps, mobile app backends, or Azure Functions hosted in Azure App Service.
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