AWS customers often look for ways to run their systems within or under budget, avoiding unnecessary costs. This post offers practical advice on designing scalable and cost-efficient three-tier architectures by using serverless technologies within the AWS Free Tier.

With AWS, you can start small and scale cost-effectively as your business demand increases. You can begin with minimal investments by using the Free Tier to build a minimum viable product (MVP). Then you can expand resources as your user base grows and your needs evolve, and transition to a full-fledged, large-scale application.

In this blog post, you will learn how to build a three-tier architecture that predominantly relies on AWS service usage within the Free Tier, resulting in a highly affordable architecture.

Note: The Free Tier offerings mentioned within this blog post are subject to change. Always check the AWS Free Tier page for the most current information.

Background: Understanding the AWS Free Tier

The Free Tier provides users with access to a range of AWS services at no cost within predefined monthly usage limits. This offering helps users to run experimentation, development, and even production workloads without charges. The Free Tier is available for more than 100 AWS products today, including Amazon Simple Storage Service (Amazon S3), Amazon Elastic Compute Cloud (Amazon EC2), and Amazon Relational Database Service (Amazon RDS). Depending on the product, there are three types of Free Tier offers:

• Free trials – Short-term trial offers that start when the first usage begins. After the trial period expires, you pay standard service rates.
• 12 months free – Offers available to new AWS customers for 12 months following their sign-up date. After the 12-month free term expires, you pay standard service rates.
• Always free – Offers available to both existing and new AWS customers indefinitely.

For example, the AWS Lambda Free Tier includes one million free requests per month and 400,000 GB-seconds of compute time per month usable for functions across both x86 and AWS Graviton processors. The AWS Lambda Free Tier falls under the always free category.

Walkthrough: Three-tier architecture on AWS

Cost efficiency is a prominent advantage of using AWS serverless services. These services decrease the need for provisioning and managing servers, reducing operational overhead and labor costs. Serverless services like AWS Lambda and Amazon API Gateway use a pay-as-you-go model. This way, you only pay for the resources you consume, providing significant savings compared to maintaining idle infrastructure. Serverless technologies also feature automatic scaling and built-in high availability to increase agility and optimize costs.

A three-tier architecture is a popular implementation of a multi-tier architecture and consists of a presentation tier, business logic tier, and data tier. A three-tier architecture separates an application’s functionality into distinct layers (presentation, business logic, and data) to enable scalability, modularity, and flexibility in software development. This type of architecture is suitable for building a wide range of applications such as web applications, enterprise systems, and mobile apps.

The following image is an example of a three-tier architecture fully built with AWS serverless services. In this example, users authenticate and navigate to the website in the presentation tier. They call APIs, which invoke Lambda functions at the business logic tier. Data is stored in DynamoDB at the data tier.

In the following sections, we explore how to use AWS serverless services within the Free Tier to build a similar architecture.

Note: The Free Tier offerings mentioned within this blog post are subject to change. Always check the AWS Free Tier page for the most current information.

Presentation tier

The presentation tier is where your users interact with your offering, such as a webpage or an app. You can use the following services within the Free Tier to build your presentation tier.

AWS service	How you can use it	Free Tier details*
Amazon S3	Host static and dynamic assets, like a React Single Page Application (SPA), and distribute them to your end users.	For the first year, you get 5 GB of standard storage, 20,000 GET requests and 2,000 PUT requests. See Amazon S3 pricing for details.
Amazon CloudFront	Use with Amazon S3 for a faster and more performant distribution of your assets to end users. CloudFront gives you access to the AWS content delivery network with more than 410 points of presence worldwide.	CloudFront includes an Always Free Tier, with 1 TB of data transfer out to the internet per month and 10 million HTTP(S) requests per month. See Amazon CloudFront pricing for details.
Amazon Cognito	Use Amazon Cognito user pools to authenticate your users. You can also integrate Amazon Cognito within your application’s UI for a seamless login experience.	Amazon Cognito has an Always Free Tier, including up to 50,000 monthly active users. It also includes 10 GBs of cloud sync storage and 1 million sync operations per month, valid for the first 12 months after sign-up. See Amazon Cognito pricing for details.

*as of September 2024

Business logic tier

The business logic tier is where code translates user actions to application functionality. You can use the following services within the Free Tier to build your business logic tier.

AWS service	How you can use it	Free Tier details*
Amazon API Gateway	Build a front door to your application’s backend by creating REST or WebSocket APIs.	Get 1 million monthly API calls for free, valid for the first 12 months after sign-up. See Amazon API Gateway pricing for details.
AWS Lambda	Use AWS Lambda for a serverless compute environment that integrates with API Gateway. You can embed your business logic into functions that run on AWS without the need for you to run and manage infrastructure.	The Always Free Tier offers 1 million free requests and 400,000 GB-seconds of compute time per month. See AWS Lambda pricing for details.

*as of September 2024

Data tier

The data tier is where your data is stored. You can use the following service within the Free Tier to build your data tier.

AWS service	How you can use it	Free Tier details*
Amazon DynamoDB	Use this serverless NoSQL database for storing data and tracking transactions. In the context of a three-tier architecture, DynamoDB stores and manages the application’s data, providing reliable and secure data access to the business logic tier.	The Always Free Tier offers 25GB of free storage, with up to 200 million requests, 25 write capacity units (WCUs), and 25 read capacity units (RCUs) per month.

*as of September 2024

Walkthrough: Monitoring your usage to avoid unexpected charges

If you use consolidated billing or AWS Organizations, the Free Tier usage accumulates at the management account level. Each management account receives one quota of the Free Tier.

To monitor your Free Tier usage and avoid unexpected charges, you can use the following resources:

• See the Free Tier page in the AWS Billing and Cost Management console. The Free Tier page provides detailed insights into current usage per service, Region, and type.
• Set up the GetFreeTierUsage API. See Using the Free Tier API for instructions.
• Set up AWS Free Tier usage alert emails.

The following image shows an example of the Free Tier page in the AWS Billing and Cost Management console.

We also recommend configuring a zero spend budget within the AWS Billing and Cost Management console. With this budget, you receive notifications when your usage exceeds the Free Tier limits, helping you to avoid unexpected charges. The following image shows an example of this budget setup.

Conclusion

In this post, we explored how to use AWS serverless services within the Free Tier to build a three-tier application. We also explored how to monitor your Free Tier usage. The Free Tier offers a chance to experiment and develop without additional costs, helping businesses minimize infrastructure expenses early on. AWS serverless architectures bring benefits like cost savings, flexibility, and scalability.

Beyond using services within the Free Tier, you can further optimize the cost of your AWS serverless application. For instance, to prevent incurring unnecessary inter-Region data transfer costs, we recommend starting with a single Region deployment for your application.

To learn more about the Free Tier and which services it offers, check out the AWS Free Tier FAQs.

Additionally, you can explore various architectural patterns for AWS serverless multi-tier architectures and the Serverless Full Stack WebApp Starter Kit to create scalable and cost-effective solutions on AWS.