1.4 The Consumption-Based Model

Quick Answer: The consumption-based (pay-as-you-go) model charges only for what you actually use — metered by the second or minute, by the GB, or per transaction. There is no mandatory hardware purchase; each meter depends on the resource, and charges may persist for storage or networking even after compute is deallocated. You can optionally commit to 1- or 3-year terms for large discounts.

Why It Matters

In traditional IT you buy hardware up front against a guess about future demand. Overestimate and you waste money on idle servers; underestimate and you cannot serve users. The consumption model lets you adjust provisioned capacity as demand changes, while billing follows each resource’s meters and configuration. For AZ-900, focus on choosing a pricing option and recognizing billing factors in a scenario.

Core principles

1. No upfront cost — no hardware purchase or mandatory contract (unless you choose a discount commitment).
2. Adjust capacity — scaling or deallocating can reduce some meters when demand falls, but attached resources may still cost money.
3. Pay for what you use — billing tracks real consumption.
4. Inspect each meter — deallocation stops VM compute charges; disks, public IPs, backups, or other retained resources may continue billing.

Azure Pricing Options

Pay-As-You-Go (PAYG)

The default: pay per second/hour/transaction with no commitment.

• Best for: unpredictable or short-term workloads, dev/test, proofs of concept.
• Flexibility: maximum — change or stop anytime.
• Discount: No commitment discount; actual price may still reflect an offer or agreement.

Reserved Instances (RIs)

Commit to a specific resource (e.g., a VM size in a region) for 1 or 3 years.

• Best for: steady-state, 24/7, predictable workloads.
• Flexibility: lower — a reservation provides a billing discount for eligible usage within its scope, subject to current exchange and refund rules; it does not guarantee deployable capacity.
• Discount: Varies by resource, region, term, and purchase option; compare current prices.

Azure Savings Plans (for compute)

Commit to a fixed hourly dollar amount of compute spend for 1 or 3 years; the discount flexes automatically across VM families and regions.

• Best for: consistent overall compute spend but changing VM mix.
• Flexibility: medium — locked to a spend rate, not a specific SKU.
• Discount: Varies by eligible compute usage and commitment; compare current prices.

Spot VMs

Buy unused Azure capacity at deep discounts; Azure can reclaim it whenever capacity is needed.

• Best for: interruptible, fault-tolerant work — batch jobs, rendering, CI/CD, dev/test.
• Flexibility: Capacity is not guaranteed; eviction can occur when Azure needs capacity, so build for interruption.
• Discount: Potentially deep and variable; Microsoft advertises up to 90% for eligible Spot VMs.

Pricing Option Comparison

How Azure Meters Usage

Billing rules you must memorize

• Inbound data (into Azure): generally free.
• Outbound data (leaving Azure): often metered and billed; rates and allowances depend on route, service, and offer.
• Deallocated (stopped) VM: compute charges stop, but disk storage charges continue.
• Deleted VM: verify disks, public IPs, backups, snapshots, and other associated resources separately; deleting the VM alone does not prove all related charges ended.

On the Exam: The classic trap question is "a stopped VM stops all charges." False — deallocation halts compute only; the OS/data disks still cost money until deleted.

Factors That Affect Cost

Cost-management tooling (also in the outline): use the Azure Pricing Calculator to estimate before deploying, the Azure Migrate business case for a broader migration comparison (outside the current calculator objective), Azure Cost Management + Billing to track and analyze actual spend, and budgets/alerts plus resource tags to govern and attribute costs.

Study focus: Match a workload to an eligible pricing option (steady usage ⇒ consider a reservation; interruptible batch ⇒ Spot; unpredictable or short use ⇒ pay-as-you-go) and check which meters continue after a resource is stopped.

Worked Scenario: Picking the Right Commitment

An analytics company runs three distinct workloads. Its production database servers run 24 hours a day, every day, with steady load — these are textbook Reserved Instance candidates, locking in potential savings for a 1- or 3-year term because the demand is fully predictable. Its data-science team runs large, restartable model-training jobs overnight that tolerate interruption — perfect for Spot VMs at variable discounts, since an eviction merely reschedules the job.

Its developers spin up short-lived test environments a few hours at a time on an unpredictable schedule — best left on Pay-As-You-Go, because committing would waste the discount on capacity they do not consistently use. If the company has consistent total compute spend but keeps changing VM families, a Savings Plan captures a discount across eligible usage without locking a specific SKU.

Azure Hybrid Benefit and Other Savings Levers

Beyond the four pricing options, AZ-900 expects you to recognize Azure Hybrid Benefit: organizations that already own Windows Server or SQL Server licenses may be able to apply eligible licenses to Azure under the current benefit terms, reducing eligible license-related charges. Combined with reservations, Hybrid Benefit can stack for substantial savings. Other levers that affect the bill include choosing a cheaper region, right-sizing the VM SKU, and reducing egress by keeping traffic within a region.

Cost-Management Tooling Summary

Common Trap: The Pricing Calculator estimates a proposed deployment, while Cost Management analyzes existing spend, and Azure Migrate can model a migration business case; the current AZ-900 cost objective names the Pricing Calculator, not a standalone TCO calculator. Match the tool to whether the scenario is planning, comparing, or monitoring — exam stems hinge on that distinction.