10.3 Serverless-Based Solution Design (Azure Functions, Logic Apps)

Why Serverless Design Matters on AZ-305

The third compute-selection objective, "Recommend a serverless-based solution," covers two distinct Azure services that both eliminate infrastructure management but solve different problems: Azure Functions (event-driven, code-first compute) and Logic Apps (workflow orchestration, low-code/visual). AZ-305 scenarios test both the choice between the two services and, once Functions is chosen, the choice of hosting plan — because the hosting plan decision drives cold start behavior, maximum execution time, and whether the app can reach private network resources at all.

Azure Functions Hosting Plans

Flex Consumption is Microsoft's current recommended default for new serverless workloads: it closes the two biggest historical Consumption-plan gaps — no VNet support and no way to reduce cold starts short of jumping straight to a Premium plan — while still billing on a scale-to-zero, per-execution basis. Configuring any always-ready instance count above zero means you are billed for that reserved capacity whether or not it executes functions, so it is a deliberate cold-start-versus-cost trade, not a free upgrade.

A Hard Ceiling Every Plan Shares

Regardless of the function app's configured timeout, any HTTP-triggered function has a hard 230-second ceiling to respond to a request — imposed by the underlying Azure Load Balancer's default idle timeout, not by the Functions runtime. A design that needs synchronous HTTP responses beyond 230 seconds must be re-architected around an asynchronous pattern (client polls a status endpoint, or a Durable Functions async HTTP API pattern), not simply by raising the functionTimeout setting.

Durable Functions Patterns

Durable Functions is an extension for building stateful workflows out of stateless functions. Recognize these named patterns for the exam:

• Function chaining — execute a sequence of functions in a specific order, passing output to the next
• Fan-out/fan-in — execute many functions in parallel, then aggregate their results
• Async HTTP API — wrap a long-running operation behind a client-polled status endpoint, working around the 230-second HTTP ceiling
• Monitor — a recurring, flexible-interval polling loop (e.g., checking an external system's state until a condition is met)
• Human interaction — a workflow that pauses for an external event such as an approval, with a timeout fallback

Logic Apps: Consumption vs. Standard

A critical 2026 exam fact: the Integration Service Environment (ISE) has been retired, so Standard is now the only Logic Apps path for a workflow that must reach a resource behind a private endpoint or an on-premises firewall — there is no longer an ISE fallback for Consumption-plan private connectivity.

Choosing Between Functions and Logic Apps

Choose Azure Functions when the solution needs custom code, complex conditional logic, or maximum performance per execution. Choose Logic Apps when the solution is primarily an orchestration of many steps across a large connector ecosystem (300+ built-in and managed connectors for SaaS and enterprise systems), needs a visual designer for business stakeholders, or requires human-in-the-loop approval steps.

Common Exam Traps

• Recommending Consumption-plan Functions for a workload that must reach a private SQL Managed Instance over a VNet — Consumption has no VNet integration; the answer must be Flex Consumption, Premium, or Dedicated.
• Assuming Durable Functions removes the 230-second HTTP ceiling — it doesn't; the ceiling is a Load Balancer limit, and Durable Functions works around it with the async HTTP API pattern, not by extending it.
• Recommending Logic Apps Consumption when the workflow needs private connectivity, forgetting ISE is retired — the correct answer is Standard.
• Treating Flex Consumption and Premium as interchangeable — Flex Consumption keeps the scale-to-zero, per-execution economics that Premium (with its required minimum instance count) does not.

Scenario Walkthrough

Adventure Works needs an image-resizing pipeline triggered by Blob Storage uploads, which must write results into a private SQL Managed Instance reachable only over a VNet, while keeping cost near zero when idle — the fit is Azure Functions on the Flex Consumption plan. A separate team needs to orchestrate a multi-day partner onboarding process spanning Outlook approval emails, a Teams notification, and an SFTP file drop with minimal custom code, and one step must reach an internal system through a private endpoint — the fit is Logic Apps Standard (Consumption is ruled out the moment private connectivity is required).