Reserved Instances and Savings Plans in AWS - Deep Dive

Overview - Reserved Instances and Savings Plans

What is it?

Reserved Instances and Savings Plans are ways to save money when using cloud computing resources by committing to use them for a longer time. Reserved Instances let you reserve specific virtual machines or services in advance, while Savings Plans offer flexible discounts based on your overall usage. Both help reduce costs compared to paying for resources only when you use them.

Why it matters

Without these options, cloud users pay the full price for resources every hour or second they run, which can add up quickly. By committing to use resources over time, users get significant discounts, making cloud computing more affordable and predictable. This helps businesses save money and plan budgets better.

Where it fits

Before learning this, you should understand basic cloud computing concepts like virtual machines and on-demand pricing. After this, you can explore advanced cost management, budgeting tools, and automated scaling strategies.

Mental Model

Core Idea

You pay less by promising to use cloud resources over time, either by reserving specific ones or by committing to spend a certain amount, gaining discounts in return.

Think of it like...

It's like buying a gym membership versus paying for each visit: a membership (Reserved Instances or Savings Plans) costs less per visit if you go regularly, while paying each time (on-demand) is more expensive if you visit often.

┌───────────────────────────────┐
│          Cloud Usage          │
├─────────────┬─────────────────┤
│ On-Demand   │ Pay full price   │
├─────────────┼─────────────────┤
│ Reserved    │ Reserve specific │
│ Instances   │ resources ahead  │
├─────────────┼─────────────────┤
│ Savings     │ Commit to spend  │
│ Plans       │ certain amount   │
└─────────────┴─────────────────┘

Build-Up - 6 Steps

1

Foundation

Understanding On-Demand Pricing

Concept: Learn how cloud resources are billed when used without any commitment.

Cloud providers charge for resources like virtual machines by the time you use them, usually per hour or per second. This is called on-demand pricing. You start and stop resources anytime and pay only for what you use, but the price per unit is the highest.

Result

You pay full price for every hour or second your resource runs, with no discounts.

Understanding on-demand pricing sets the baseline for why reserved options exist to save money.

2

Foundation

What Are Reserved Instances?

Concept: Reserved Instances let you book specific cloud resources in advance for a lower price.

You choose a resource type, region, and term length (usually 1 or 3 years) and pay upfront or monthly. In return, you get a discount compared to on-demand prices. This reservation guarantees capacity and lower cost for that resource.

Result

You pay less per hour for the reserved resource, but you commit to using it for the term.

Knowing reserved instances means understanding commitment leads to cost savings and capacity guarantees.

3

Intermediate

How Savings Plans Differ

🤔Before reading on: do you think Savings Plans require reserving specific resources like Reserved Instances? Commit to your answer.

Concept: Savings Plans offer flexible discounts based on your total spend, not tied to specific resources.

Instead of reserving a specific machine, you commit to spend a fixed amount per hour for 1 or 3 years. This discount applies to any eligible usage, across instance types, regions, or even services, giving more flexibility than Reserved Instances.

Result

You get discounts on a wide range of resources without locking into one type or region.

Understanding Savings Plans shows how flexibility can coexist with cost savings.

4

Intermediate

Types of Reserved Instances and Savings Plans

🤔Before reading on: do you think all Reserved Instances and Savings Plans require full upfront payment? Commit to your answer.

Concept: There are different payment options and types for both Reserved Instances and Savings Plans.

Reserved Instances can be Standard (fixed) or Convertible (changeable), with payment options: All Upfront, Partial Upfront, or No Upfront. Savings Plans come as Compute Savings Plans (flexible across compute services) and EC2 Instance Savings Plans (more specific but cheaper).

Result

You can choose payment and commitment types that fit your budget and flexibility needs.

Knowing these types helps tailor cost-saving strategies to real business needs.

5

Advanced

How AWS Applies Discounts Automatically

🤔Before reading on: do you think you must manually assign Reserved Instances or Savings Plans to each resource? Commit to your answer.

Concept: AWS automatically applies your Reserved Instances or Savings Plans discounts to matching usage.

When you run resources, AWS checks your reservations or plans and applies discounts to matching usage first. If you have unused reservations, they can sometimes apply to similar resources in the same region. This automatic matching maximizes your savings without manual effort.

Result

You get the best possible discount applied automatically to your usage.

Understanding automatic discount application prevents confusion about billing and ensures you optimize your commitments.

6

Expert

Optimizing Commitments for Cost and Flexibility

🤔Before reading on: do you think committing to more Reserved Instances or Savings Plans always saves more money? Commit to your answer.

Concept: Balancing commitment size, term length, and flexibility is key to maximizing savings without waste.

Experts analyze usage patterns to decide how many Reserved Instances or Savings Plans to buy. Overcommitting wastes money if usage drops; undercommitting misses savings. They also mix Standard and Convertible Reserved Instances or different Savings Plans types to balance cost and flexibility. Tools and reports help track and adjust commitments over time.

Result

You achieve the lowest cost with the right balance of commitment and flexibility.

Knowing how to optimize commitments avoids common costly mistakes and adapts to changing needs.

Under the Hood

Behind the scenes, AWS tracks your usage and matches it against your Reserved Instances or Savings Plans commitments. Reserved Instances are recorded as capacity reservations tied to specific instance attributes, while Savings Plans track your committed spend amount. When you launch resources, AWS billing applies discounts by comparing usage to these commitments, prioritizing the best match to maximize savings.

Why designed this way?

AWS designed Reserved Instances and Savings Plans to encourage longer-term commitments, which help AWS plan capacity and revenue predictably. Reserved Instances offer capacity guarantees, important for steady workloads, while Savings Plans provide flexibility for changing needs. This dual approach balances customer cost savings with AWS operational efficiency.

┌───────────────┐       ┌─────────────────────┐
│ User Usage   │──────▶│ AWS Billing System   │
└───────────────┘       ├─────────────────────┤
                        │ Matches usage with  │
┌───────────────────┐   │ Reserved Instances  │
│ Reserved Instances│◀──│ and Savings Plans   │
│ & Savings Plans   │   └─────────────────────┘
└───────────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do Reserved Instances guarantee you always pay less than on-demand? Commit yes or no.

Common Belief: Reserved Instances always cost less than on-demand pricing.

Reality: Reserved Instances cost less only if you use the reserved resource as planned; unused reservations still incur charges without usage benefit.

Why it matters: Failing to use reserved capacity leads to wasted money, negating expected savings.

Quick: Do Savings Plans require you to use the same instance type or region? Commit yes or no.

Common Belief: Savings Plans discounts apply only to specific instance types or regions.

Reality: Compute Savings Plans apply discounts broadly across instance types, sizes, and regions, offering more flexibility than Reserved Instances.

Why it matters: Misunderstanding this limits your ability to optimize costs with flexible usage.

Quick: Can you manually assign Reserved Instances discounts to any resource? Commit yes or no.

Common Belief: You must manually assign Reserved Instances discounts to each resource you run.

Reality: AWS automatically applies Reserved Instances discounts to matching usage; manual assignment is not needed.

Why it matters: Thinking manual assignment is required causes unnecessary management overhead and confusion.

Quick: Does buying more Reserved Instances or Savings Plans always save more money? Commit yes or no.

Common Belief: The more Reserved Instances or Savings Plans you buy, the more money you save, no matter what.

Reality: Overcommitting beyond your actual usage wastes money because you pay for unused capacity or spend commitments.

Why it matters: Overcommitting leads to higher costs, defeating the purpose of savings plans.

Expert Zone

1

Reserved Instances can sometimes be sold on a marketplace if no longer needed, recovering some costs.

2

Convertible Reserved Instances allow changing instance types during the term, but usually at a smaller discount than Standard ones.

3

Savings Plans billing applies at the account level, so consolidated billing can maximize discount usage across multiple accounts.

When NOT to use

Avoid Reserved Instances or Savings Plans if your workload is highly unpredictable or short-term, as commitments can lead to wasted costs. Instead, use on-demand or spot instances for maximum flexibility and cost efficiency.

Production Patterns

Large organizations use a mix of Reserved Instances for steady baseline workloads and Savings Plans for variable or growing usage. They monitor usage with cost management tools and adjust commitments quarterly or annually to optimize savings.

Connections

Budgeting and Forecasting

Builds-on

Understanding Reserved Instances and Savings Plans helps create accurate cloud budgets and forecasts by predicting committed costs.

Subscription Models in Business

Same pattern

Both cloud savings plans and subscription services rely on upfront commitment for discounted pricing, balancing customer loyalty and predictable revenue.

Energy Utility Contracts

Similar concept

Just like reserving energy capacity or signing fixed-rate contracts reduces costs and ensures supply, cloud reserved options manage resource use and pricing predictably.

Common Pitfalls

#1 Buying Reserved Instances without analyzing actual usage patterns.

Wrong approach:

Purchase 10 Reserved Instances for a resource you only use 5 hours a week.

Correct approach:

Analyze usage data and buy Reserved Instances matching steady baseline usage, e.g., 2-3 instances for consistent hours.

Root cause:

Misunderstanding commitment means paying regardless of actual usage leads to wasted costs.

#2 Assuming Savings Plans cover all AWS services.

Wrong approach:

Expect Savings Plans discounts to apply to storage or database services.

Correct approach:

Use Savings Plans only for eligible compute services; manage other services with separate cost controls.

Root cause:

Confusing eligible services causes unexpected charges and budgeting errors.

#3 Trying to manually assign Reserved Instances discounts to resources.

Wrong approach:

Manually tagging instances to apply Reserved Instance discounts.

Correct approach:

Let AWS automatically apply discounts; focus on purchasing the right reservations.

Root cause:

Misunderstanding AWS billing automation leads to unnecessary manual work and errors.

Key Takeaways

Reserved Instances and Savings Plans reduce cloud costs by committing to use or spend over time.

Reserved Instances reserve specific resources and offer capacity guarantees, while Savings Plans provide flexible discounts across usage.

AWS automatically applies discounts to matching usage, so manual assignment is not needed.

Choosing the right type and amount of commitment requires analyzing usage patterns to avoid wasted costs.

These cost-saving options help businesses plan budgets and optimize cloud spending effectively.