On-demand Capacity Reservation in Azure - Azure Virtual Machines

Introduction

• On-demand capacity reservation allows reserving compute capacity in Azure for any duration, without long-term commitments.
• Available for both Windows and Linux VMs, supporting both uniform and flexible scale sets.

Benefits

• Immediate Usage: Use resources immediately after reservation creation.
• Flexibility: Create/delete reservations anytime.
• Control: Target critical workloads, noncritical workloads run without reserved capacity.

Key Properties

• VM Size: Each reservation is specific to a VM size (e.g., Standard_D2s_v3).
• Location: Specific to a region or availability zone.
• Quantity: Number of instances reserved.

Reservation Process

• Creation: Requires passing parameters like VM size, location, quantity.
• Quota: Requires adequate subscription quota; requests can fail for insufficient quota.

Benefits and Usage

• SLA: Provides capacity guarantee within service-level agreements.
• Flexibility: Combine with reserved instances for discounts.
• No Term Commitment: Capacity can be deployed/deleted anytime.

Limitations & Restrictions

• Supported VM Series: Limited to specific series (e.g., Av2, B, D, E series).
• Deployment Types Supported: Single VM, VM scale sets with uniform/flexible orchestration.
• Unsupported Types: Spot VMs, Azure Dedicated Host nodes, availability sets, etc.
• Constraints: No support for proximity placement, update domains, specific disk storage options, etc.

Pricing & Billing

• Pricing: Same as underlying VM size, charged at pay-as-you-go rates.
• Billing: Charges for the reservation, even if unused, eligible for discounts with reserved instances.

Differences from Reserved Instances

• Term: No commitment vs. fixed-term for reserved instances.
• Billing: Pay-as-you-go vs. discounted rates.
• Capacity SLA: Provides capacity guarantee, unlike reserved instances.

Capacity Reservation Lifecycle

• Group Management: Defined per VM size and region.
• Adjustment: Reservation quantity adjustable post-deployment.
• Deletion: Requires dissociation of VMs before deletion.

Usage Scenarios

• Ideal for business continuity, disaster recovery, and scaling mission-critical applications.

FAQs

• Pricing: Charged at VM size rates, no double charging.
• Discounts: Reserved VM instances can apply to reservations.
• Scenario Suitability: Best for continuity and critical application scaling.

Additional Resources

• Create, modify, associate, and manage capacity reservations through Azure documentation and tutorials.