Three-Tier Web Apps on AWS

What is a three-tier web application?

A three-tier web application is a type of software architecture that is organized into three distinct layers, each with a specific set of responsibilities. These tiers are the presentation tier, the application logic tier, and the data storage tier.

Imagine a three-tier web application as a multi-story building. The presentation tier is like the lobby of the building, where visitors enter and interact with the application. The application logic tier is like the offices on the upper floors, where business logic and decision-making happen. And the data storage tier is like the basement of the building, where all the important documents and records are kept safe and organized.

Each of these tiers works together to make the web application function smoothly and efficiently. The presentation tier handles the user interface and user experience, the application logic tier handles the business logic and data processing, and the data storage tier handles the storage and management of the data.

A three-tier architecture is a modular and scalable way to organize a web application, allowing different components to be developed and maintained independently and allowing the application to easily adapt to changing requirements and workloads.

The tiers in more detail

In a three-tier web application, the three tiers are typically referred to as the presentation tier, the application logic tier, and the data storage tier.

1. The presentation tier, also known as the client tier, is the front end of the application that users interact with. This tier typically consists of HTML, CSS, and JavaScript files that are delivered to the user’s browser, as well as any client-side logic that is executed in the browser.
2. The application logic tier, also known as the middle tier or server tier, is the part of the application that handles the business logic and communicates with the presentation and data storage tiers. This tier may include server-side scripting languages such as PHP, Python, or Ruby, as well as application servers and other supporting software.
3. The data storage tier, also known as the database tier, is responsible for storing and managing the data used by the application. This tier may include databases such as MySQL, Oracle, or MongoDB, as well as other data storage technologies such as Amazon S3 or Azure Blob Storage.

Each of these tiers is typically separated from the others and communicates with them through APIs or other types of interfaces. This separation of concerns allows for a more modular and scalable application architecture.

What are some benefits of a three-tier web application?

A three-tier web application offers several benefits over other types of web application architectures. Here are some benefits of a three-tier web application, using a creative analogy:

1. Modularity: Each tier of a three-tier web application can be thought of as a puzzle piece that fits together with the other tiers to form the complete application. This modular design allows different pieces to be developed and maintained independently, making it easier to update or replace specific parts of the application without affecting the whole.
2. Scalability: A three-tier web application can be scaled up or down as needed to meet changing traffic and workload demands. Imagine each tier as a set of building blocks that can be added or removed as needed to increase or decrease the size of the application.
3. Security: The separation of concerns in a three-tier web application helps to improve security by limiting access to sensitive data and business logic. Imagine each tier as a locked door that can only be accessed by certain people with the right key or credentials.
4. Performance: By distributing the workload across different tiers, a three-tier web application can improve performance and reduce the risk of bottlenecks. Imagine each tier as a different cog in a machine, all working together to complete a task efficiently.

What are some drawbacks to a three-tier web application?

There are a few potential downsides to using a three-tier web application architecture:

1. Complexity: A three-tier web application can be more complex to design, develop, and maintain than a single-tier or two-tier application. There are more components to integrate and manage, and the interactions between the tiers can be more difficult to understand and troubleshoot.
2. Cost: A three-tier web application may require more resources and infrastructure to run, which can increase the cost of hosting and maintaining the application.
3. Deployment challenges: Deploying a three-tier web application can be more complex than deploying a single-tier or two-tier application, especially if the tiers are deployed on different servers or in different locations.

The benefits of a three-tier web application may outweigh these potential downsides, depending on the specific requirements and complexity of the application. However, it is important to carefully consider the trade-offs and potential challenges when deciding whether to use a three-tier architecture.

Network Topology

Here are three common network topologies that you might consider for your three-tier web application in AWS:

1. Public-facing load balancer: In this configuration, the presentation tier (front-end) of your application is accessed through a public-facing Amazon Elastic Load Balancer (ELB) or Amazon Application Load Balancer (ALB), which distributes incoming traffic across an Auto Scaling Group or multiple Amazon Elastic Compute Cloud (EC2) instances in a private subnet. The application logic tier (middle tier) and data storage tier (back-end) are also hosted on EC2 instances in private subnets. This topology allows you to expose your application to the internet while keeping the application servers and data storage resources private and secure.
2. Multiple Availability Zones: In this configuration, the EC2 instances hosting the presentation, application logic, and data storage tiers are distributed across multiple Availability Zones (AZs) within the same AWS Region. This can provide higher availability and resilience in case of failures or disruptions in a single AZ. A load balancer can be used to distribute traffic across the EC2 instances in different AZs.
3. VPC peering: In this configuration, the EC2 instances hosting the different tiers of your application are located in separate Amazon Virtual Private Clouds (VPCs) that are connected through VPC peering. This allows you to isolate the different tiers of your application into separate networks, while still allowing them to communicate with each other through private IP addresses.

These are just a few examples of network topologies that you might consider for a three-tier web application in AWS. The best topology for your application will depend on your specific requirements and needs.

How can you host the presentation tier?

There are several ways to host the presentation tier of a three-tier web application on Amazon Web Services (AWS). Here are a few options to consider:

1. Amazon Elastic Compute Cloud (EC2): EC2 is a scalable, highly available, and flexible cloud computing service that allows you to launch and configure virtual machines (instances) to host your applications. EC2 instances come in different sizes and configurations, so you can choose the instance type that best meets the needs of your application. To host the presentation tier on EC2, you can install a web server, such as Apache or Nginx, on the instances and configure it to serve static assets such as HTML, CSS, and JavaScript files, as well as any server-side scripting languages that you may be using.
   
   Pros: EC2 allows you to have full control over the instances and the software that is installed on them, which can be useful if you have specific requirements or need to customize the environment. EC2 instances are also highly available and can be configured to automatically scale up or down based on demand.
   
   Cons: EC2 instances can be more expensive to run compared to other options, and you will need to manage the instances and the software that is installed on them, which can be time-consuming.
2. Amazon Elastic Load Balancer (ELB) or Amazon Application Load Balancer (ALB): ELB and ALB are fully managed load balancers that distribute incoming traffic across multiple targets, such as EC2 instances, containers, or IP addresses. You can use ELB or ALB to host the presentation tier of your web application by configuring it to forward traffic to the instances or targets that are hosting your static assets and server-side logic. ELB is a layer 4 (transport layer) load balancer that can route traffic based on IP address and TCP port, while ALB is a layer 7 (application layer) load balancer that can route traffic based on the hostname, path, and other HTTP request parameters.
   
   Pros: ELB and ALB can improve the availability and scalability of your presentation tier by distributing incoming traffic across multiple targets. They are also easy to use and require minimal setup and maintenance.
   
   Cons: ELB and ALB are primarily designed to distribute traffic and may not be suitable for hosting dynamic content or executing server-side logic. You will also need to manage the targets that are registered with the load balancer and ensure that they are properly configured and secured. ELB and ALB may also be more expensive to run compared to other options, depending on your usage patterns.
3. Amazon Simple Storage Service (S3): S3 is a highly available and scalable object storage service that allows you to store and retrieve any amount of data at any time, from anywhere on the web. To host the presentation tier on S3, you can upload your static assets such as HTML, CSS, and JavaScript files to S3 and configure them to be publicly accessible. You can then use the S3 URLs to reference the assets in your application.
   
   Pros: S3 is highly available and scalable, and can be a cost-effective option for storing and serving static assets. It is also easy to use and requires minimal setup and maintenance.
   
   Cons: S3 is not designed to host dynamic content or execute server-side logic, so you will need to use other services or infrastructure to handle these tasks. You will also need to manage the assets that are stored in S3 and ensure that they are properly configured and secured.
4. Amazon CloudFront: CloudFront is a content delivery network (CDN) that speeds up the delivery of static assets by serving them from edge locations around the world. To host the presentation tier on CloudFront, you can create a CloudFront distribution and configure it to fetch the assets from an S3 bucket, an EC2 instance, or another origin. You can then use the CloudFront URLs to reference the assets in your application.
   
   Pros: CloudFront can deliver static assets to users with low latency, which can improve the performance and user experience of your application. It is also highly available and scalable and can be a cost-effective option depending on your usage patterns.
   
   Cons: CloudFront is primarily designed to deliver static assets, and may not be suitable for hosting dynamic content or executing server-side logic. You will also need to manage the assets that are stored in the origin and ensure that they are properly configured and secured.

These are just a few examples of how you can host the presentation tier of a three-tier web application on AWS. The best option for your application will depend on your specific requirements and needs.

How can you host the application tier?

1. Amazon Elastic Compute Cloud (EC2): Refer back to the EC2 info in the presentation tier for more details.

2. Amazon Elastic Container Service (ECS): ECS is a fully managed container orchestration service that makes it easy to deploy, run, and scale containerized applications. A container is a lightweight and portable package that includes the code, runtime, system tools, and libraries needed to run an application. By using containers, you can package your application and its dependencies into a single, self-contained unit that can be easily deployed and run on any infrastructure. To host the application tier on ECS, you will need to containerize your application and deploy it to ECS using Amazon Elastic Container Registry (ECR) or a third-party container registry.
   
   Pros: ECS makes it easy to deploy and manage containerized applications, and allows you to scale your application up or down as needed. Containers are also portable and can be run on any infrastructure, which can be useful if you need to deploy your application in different environments or regions.
   
   Cons: Containerizing your application can require some upfront work, and you will need to manage the containerized application and the underlying infrastructure, such as the EC2 instances that are used to host the containers. ECS may also be more expensive to run compared to other options, depending on your usage patterns.

3. AWS Lambda: AWS Lambda is a compute service that allows you to run code in response to events and automatically scales to meet demand. With Lambda, you can create functions that are triggered by specific events, such as an HTTP request, a change to a database, or a message on a message queue. To host the application tier on Lambda, you will need to create one or more functions that handle the business logic and data processing for your application and configure the functions to be triggered by the appropriate events.
   
   Pros: Lambda allows you to run code in a fully managed and scalable environment, and only charges you for the compute time that you use. This can make Lambda a cost-effective option, especially if your application has infrequent or unpredictable workloads.
   
   Cons: Lambda has some limitations on the execution environment and the resources that are available to your functions, which may not be suitable for all applications. You will also need to design your application to be event-driven and split your logic into small, independent functions, which may require some upfront work.

How can you host the data tier?

1. Amazon Relational Database Service (RDS): RDS is a fully managed database service that makes it easy to set up, operate, and scale a relational database, such as MySQL, PostgreSQL, or Oracle, in the cloud. To host the data tier on RDS, you can create a database instance and configure it to store the data for your application. RDS handles tasks such as patching, backups, and failover automatically, and allows you to scale the database up or down as needed.
   
   Pros: RDS is a fully managed service that takes care of many of the routine database tasks, such as backups, patches, and failovers. It is also highly available and scalable and can be a cost-effective option depending on your usage patterns.
   
   Cons: RDS is a proprietary service and is limited to a few specific database engines. It may also be more expensive to run compared to other options, depending on your usage patterns.

3. Amazon DynamoDB: DynamoDB is a fully managed, fast, and scalable NoSQL database service that allows you to store and retrieve any amount of data at any time, from anywhere on the web. To host the data tier on DynamoDB, you can create tables and configure them to store the data for your application. DynamoDB handles tasks such as scaling, backups, and failover automatically, and allows you to scale the database up or down as needed. Here are some DynamoDB security best practices: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/best-practices-security-preventative.html
   
   Pros: DynamoDB is a fully managed service that takes care of many of the routine database tasks, such as scaling, backups, and failover. It is also highly available and scalable and can be a cost-effective option depending on your usage patterns.
   
   Cons: DynamoDB is a proprietary service and is limited to a single database engine (NoSQL). It may also be more expensive to run compared to other options, depending on your usage patterns.