Architecting on AWS: the Best Services to Build a Two-Tier Application

The notion of a scalable, on-demand, pay-as-you-go cloud infrastructure tends to be easily understood by the majority of today’s IT specialists. However, in order to fully reap the benefits from hosting solutions in the cloud, you will have to rethink traditional ‘on-premises’ design approaches. This should happen for a variety of reasons with the most prominent ones the design-for-costs or the adoption of a design-for-failure approach.

This is the first of a series of posts in which we will introduce you to a variety of entry-level AWS services on the example of architecting on AWS to build a common two-tier application deployment (e.g. mod_php LAMP). We will use the architecture to explain common infrastructure and application design patterns pertaining to cloud infrastructure.

To start things off we provide you with a high-level overview of the system and a brief description of the utilized services.
Architecting on AWS

Virtual Private Cloud (VPC)

The VPC allows you to deploy services into segmented networks to reduce the vulnerability of your services to malicious attacks from the internet. Separating the network into public and private subnets allows you to safeguard the data tier behind a firewall and to only connect the web tier directly to the public internet. The VPC service provides flexible configuration options for routing and traffic management rules.  Use an Internet Gateway to enables connectivity to the Internet for resources that are deployed within public subnets.

Redundancy

In our reference design, we have spread all resources across two availability zones (AZ) to provide for redundancy and resilience to cater for unexpected outages or scheduled system maintenance. As such, each availability zone is hosting at least one instance per service, except for services that are redundant by design (e.g. Simple Storage Service, Elastic Load Balancer, Rote 53, etc.).

Web Tier

Our web tier consists of two web servers (one in each availability zone) that are deployed on Elastic Compute Cloud (EC2) instances. We balance external traffic to the servers using Elastic Load Balancers (ELB). Dynamic scaling policies allow you to elastically scale the environment in adding or removing web instances to the auto scaling group. Amazon Cloud Watch allows us to monitor demand on our environment and triggers scaling events using Cloud Watch alarms.

Database Tier

Amazon’s managed Relational Database Service (RDS) provides the relational (MySQL, MS SQL or Oracle) environment for this solution. In this reference design, it is established as a multi-AZ deployment. The multi-AZ deployment includes a standby RDS instance in the second availability zone, which provides us with increased availability and durability for the database service in synchronously replicating all data to the standby instance.

Optionally we can also provision read replicas to reduce the demand on the master database. To optimize costs, our initial deployment may only include the master and slave RDS instances, with additional read replicas created in each AZ as dictated by the demand.

Object store

Our file objects are stored in Amazon’s Simple Storage Service (S3). Objects within S3 are managed in buckets, which provide virtually unlimited storage capacity. Object Lifecycle Management within an S3 bucket allows us to archive (transition) data to the more cost-effective Amazon Glacier service and/or the removal (expiration) of objects from the storage service based on policies.

Latency and user experience

For minimized latency and enhanced user experience for our worldwide user base, we utilize Amazon’s CloudFront content distribution network. CloudFront maintains a large number of edge locations across the globe. An edge location acts as a massive cache for web and streaming content.

Infrastructure management, monitoring, and access control

Any AWS account should be secured using Amazon’s Identity and Access Management (IAM). IAM allows for the creation of users, groups, and permissions to provide granular, role-based access control over all resources hosted within AWS.

The provisioning of the above solution to the regions is achieved in using Amazon CloudFormation. CloudFormation supports the provisioning and management of AWS services and resources using scriptable templates. Once created, CloudFormation also updates the provisioned environment based on changes made to the ‘scripted infrastructure definition’.
We use the Route 53 domain name service for the registration and management of our Internet domain.

In summary, we have introduced you to a variety of AWS services, each of which has been chosen to address one or multiple specific concern in regards to functional and non-functional requirements of the overall system. In our upcoming posts, we’ll investigate a number of above services in more detail, discussing major design considerations and trade-offs in selecting the right service for your solution. In the meantime, you can start to learn more about the individual AWS services using AWS Learning Paths that are available on the Cloud Academy library.

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Written by

Christian Petters

As a Solutions Architect, Christian is helping organisations to find the most appropriate solution to address their unique business problems. He is passionate about the opportunities that are provided by modern cloud services and covers topics in AWS and MS Azure with a particular focus on Microsoft technologies.


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