A comprehensive overview of AWS costs: A systematic explanation of pricing, estimates, and management

Amazon Web Services (AWS)Many companies have introduced it because they heard it was cheap because it was a pay-as-you-go system, but once they started using it, they often found themselves wondering why their monthly bill was increasing or not, or wondering which resource was causing the increased costs.

In this article, we will clarify the structure of AWS costs, which tend to be a black box. Rather than simply explaining how to calculate them, we will explain common pitfalls when estimating costs and key points for managing bills to prevent them from getting out of control, following a practical flow.

AWS costs are determined by "usage" + "design and operation"

AWS is a pay-as-you-go system, so the cost seems simple when you just look at the explanation that you "pay only for what you use." However, the actual amount you are billed will vary greatly depending on which services you use, in what configuration, and how you operate them, rather than the amount of usage itself.

There are two reasons why AWS can be cheap or expensive. The first is pure usage, such as the number of instances, storage capacity, and data transfer volume. The other is design and operational decisions, such as redundant configurations, resource allocation, and operational rules for suspension and deletion. The latter is difficult to grasp from the price list, and can unintentionally drive up costs.

Therefore, AWS cost issues cannot be solved by simply understanding the pricing schedule. What's important is understanding the structure of which choices result in costs and where. If you estimate or operate without understanding this structure, you won't be able to identify the reason why your bill deviates from your expectations.

The four major cost factors and pitfalls of AWS

AWS costs are not a collection of small fee items, but can be seen in the bigger picture by breaking them down into several components. The important thing is to distinguish and understand which components tend to increase and which are easily overlooked.

Resources that continue to be charged even when stopped, and resources that stop

It is often thought that stopping a resource will stop the charges, but this is not necessarily the case. For example, even if you stop an EC2 instance, charges will continue to be incurred for the attached EBS volume as long as it is retained. Similarly, charges will be incurred for Elastic IP addresses if they are reserved and unused.

If you don't understand this difference and think that "stopping" means "zero cost," you'll continue to be charged for an environment that you're not using. The first pitfall in AWS costs is that the relationship between resource status and billing doesn't match.

The four basic elements: calculation, storage, transmission, and management

AWS costs generally consist of four components:

1. Compute: Execution resources such as EC2 and Lambda

2. Storage: Data retention such as EBS, S3, snapshots, etc.

3. Data Transfer: Internet-facing, inter-AZ, inter-region communications

4. Management: Operational costs such as monitoring, logging, backups, and support

When making estimates, attention tends to be focused on computing resources, but the elements of storage, transfer, and management tend to pile up later and have an effect during the operational phase. Management costs in particular are often overlooked as "necessary expenses," and by the time you realize it, they can have become a significant amount.

Data transfer: the most complex and costly

Of the four elements, data transfer is the most difficult to understand and the easiest to misinterpret. Billing conditions vary depending on the transfer route, such as outbound communication to the Internet, communication across availability zones, or communication between regions.

While it is difficult to notice this during the design stage, costs can rise rapidly due to increases in traffic volume or configuration changes.

Why AWS bills exceed budgets

There is no single cause for AWS bills exceeding expectations. In many cases, the bills are caused by a combination of costs not anticipated at the estimation stage and costs that continue to increase after operations begin. This is not a sudden accident, but a structural phenomenon that is likely to occur.

Estimation Blind Spots: NAT Gateway, Snapshots, and CloudWatch Logs

While estimates tend to focus on core resources such as EC2 and RDS, it is often peripheral resources such as NAT Gateway, snapshots, and CloudWatch Logs that actually drive up your bill.

NAT Gateways are commonly deployed to ensure availability, but because they are charged based on communication volume, the impact increases as traffic increases. Snapshots are retained as "insurance," and capacity tends to increase without generation management. CloudWatch Logs can also add up to unnoticed costs if you are not mindful of the log output volume and retention period.

Even if it seems small on its own, if you start operation without including it in the estimate, it will later become apparent as a difference from the budget.

Abandonment after production: The ghost cost of zombie instances and testing environments

Another factor is the increase in costs due to neglect after the start of operation. If unused instances and resources are left behind without being stopped or deleted, unintended charges will occur.

In many cases, a temporary testing environment or an instance that has outlived its usefulness is left as is. When AWS bills exceed budget, it is often the result of these small oversights and neglect that accumulate, rather than major configuration errors.

Estimation steps to avoid failure

The important thing about AWS estimates is not the operation of the tool itself, but the assumptions on which the figures are calculated. If the assumptions are unclear, the estimate may appear correct, but it will easily fall apart in actual operation.

Explaining the prerequisites for using the AWS Pricing Calculator

The Pricing Calculator is a powerful tool, but if you enter the wrong assumptions, the figures you get will be far from reality. The minimum you should do before getting a quote is to organize the following:

• Operating hours (24 hours or business hours only)

• Number of units and redundant configuration (including production and standby systems)

• Instance performance (are you overestimating the performance?)

• Data volume and growth rate (is it just the initial value?)

• Region (Tokyo or other region)

A common mistake is estimating with the "minimum configuration." In production, the configuration will be increased to take into account availability and operational load, and differences will arise at this stage.

Addition of "peripheral costs" assuming actual operation

When making an estimate, you must also include costs other than the main resource, such as the following:

• AWS Support Plan Costs

• Backup and snapshot storage costs

• Operational costs associated with monitoring and logging

• Security measures and additional service fees

These are often items that become necessary later and are easily overlooked in initial estimates, but because they are unavoidable in production operations, they are also costs that should be included from the beginning.

Three management techniques to make billing more predictable

The key to AWS cost management is not to reduce billing amounts, but to ensure that costs do not deviate from expectations. Rather than searching for the cause after an issue has occurred, you need a system that can quickly identify signs of an increase and instantly understand what is happening and where.

AWS Budgets: Detecting Anomalies Through Predictive Insights

AWS Budgets is not a feature for limiting costs, but is primarily used as a mechanism for early detection of anomalies. By setting monthly budgets and service-specific limits, you can receive notifications if costs are increasing faster than expected.

The important thing is not to rely too strictly on the budget amount. The aim is to set a line with some leeway so that you can detect any "unusual movements."

Cost Explorer: Identifying the culprits behind rising costs

Cost Explorer is a tool that helps you identify the reasons for an increase in your bill. You can view changes in costs by service, account, or day, and quickly identify where the increase is occurring.

The key is to look at the trend compared to the previous month or over the last few days. Rather than just focusing on the total amount, if you can understand when and for which service the increase started, you can pinpoint the cause.

Cost Allocation Tags: Gain visibility into who's spending and what they're spending for

Cost allocation tags are essential to the effectiveness of Budgets and Cost Explorer, allowing you to break down costs by project, environment, or department.

Without tags, you can see that the amount is increasing, but you cannot see who made the decision or what it is being used for. At the very least, by tagging the amount by environment (production/verification), purpose, project, etc., cost management will become practical.

How to proceed with cost optimization

A common mistake when optimizing AWS costs is thinking about "discounts" and "reservations" first. In practice, getting the order wrong can lead to waste rather than optimization. The key is to organize what you're paying for now before deciding on future payments.

STEP 1: Cleaning (deleting and stopping unnecessary resources)

The first thing to do is to clean up your environment. Delete or stop any unnecessary resources, such as unused instances, testing environments that have outlived their usefulness, and abandoned load balancers and IP addresses.

This stage does not involve changing settings or revising the design, so it is characterized by the lowest risk and the highest chance of success. Nevertheless, it tends to be put off because in many cases, it is unclear who is authorized to delete it.

STEP 2: Optimization (rightsizing and modernization)

The next step is resource optimization, which structurally reduces costs by scaling down instances with excessive specifications and replacing processes that do not need to be running constantly with on-demand services.

At this stage, it is important to make decisions based on actual usage, such as CPU and memory usage. If you apply the discount option beforehand when there is still room to reconsider the design, the freedom to make improvements will be reduced.

STEP 3: Purchase reservation (Savings Plans / RI application)

Finally, there are purchase reservations such as Savings Plans and Reserved Instances. These are only effective if your usage is stable.

Once you have completed the cleaning and optimization, it will be easier to decide that "this configuration will remain the same for the time being." By making reservations under this condition, you can take advantage of the discount without locking in any waste.

Cost optimization is not a matter of technique, but of order. By following this golden order, you can achieve continuous optimization in a natural way.

AWS Cost Management FAQs

Can I pay for AWS in Japanese yen?

AWS usage fees are calculated in US dollars, and actual payments are made in Japanese yen based on the conversion rate set by your credit card company or billing agent. As a result, billing amounts may increase or decrease from the previous month due to exchange rates, even if usage remains unchanged. When managing costs, it is necessary to consider changes in usage and exchange rate factors separately.

How much can I use the free tier?

AWS has a free usage tier, but the services covered, the period, and the upper limit are limited. While it is effective for testing purposes, when it comes to production operations, there are almost no cases where the free tier alone can cover the costs.

In what cases will it be more expensive than on-premise?

Depending on how you use AWS, costs can be higher than on-premises. Typical examples include migrating a system that is constantly running under high load, or using a configuration with a large amount of data transfer. Configurations that do not take advantage of AWS's features make it difficult to realize the benefits of pay-as-you-go pricing.

What settings should be done from the beginning, even on a small scale?

Regardless of the scale, it is important to set up a cost visualization and notification system from the beginning. Specifically, set up budget alerts using AWS Budgets and set up a minimum of cost allocation tags. If you put these off until later, you will not be able to track down the cause when a problem occurs.

My Feelings, Then and Now

AWS costs are not simply determined by the amount used. They vary greatly depending on the design and management of which services are used, in what configuration, and how they are operated. Therefore, cost issues cannot be resolved by simply looking at price lists and discount systems.

The important thing is to understand the structure in which costs are incurred, organize the assumptions at the estimation stage, and maintain a state in which you can grasp the signs of costs after the start of operation. Discount options only become meaningful once unnecessary resources have been eliminated and the configuration has been optimized.

AWS cost management is not about techniques to make things cheaper, but about designing and operating to create predictable conditions. Having this perspective will determine whether you are at the mercy of your bill or can control it.