Autoscaling Web Tier on AWS
A dependable three-tier AWS web architecture with an autoscaling EC2 compute tier, Multi-AZ RDS, ElastiCache, and CloudFront. It is simple and well understood, with OS management and reactive scaling as the main trade-offs.
Overview
This is the proven three-tier web architecture: a presentation and edge layer, an elastic compute tier, and a managed data tier. Use it for traditional web applications, content sites, and APIs where you want straightforward operations and predictable scaling without adopting containers or serverless. It is the right starting point for most teams moving a workload to AWS.
The compute tier scales automatically with demand, so you pay for capacity that matches traffic rather than peak provisioning.
Components
- Application Load Balancer (ALB): Distributes HTTP traffic across healthy instances and terminates TLS.
- EC2 Auto Scaling group: Elastic fleet of application servers that grows and shrinks on demand.
- RDS: Managed relational database (PostgreSQL or MySQL) with Multi-AZ failover.
- ElastiCache: Managed Redis for sessions and query caching.
- CloudFront: CDN caching static and dynamic content at the edge.
- S3: Object storage for static assets, uploads, and backups.
- CloudWatch: Metrics, alarms, and logs driving the scaling policies.
Data Flow
Users reach CloudFront, which serves cached assets from S3 and forwards dynamic requests to the ALB. The ALB routes to an EC2 instance in the Auto Scaling group. The application checks ElastiCache for cached data, falling back to RDS for the system of record. Static uploads are written to S3. CloudWatch collects request and resource metrics; when load crosses a threshold, the Auto Scaling group launches or terminates instances from a hardened machine image.
Scaling and Resilience
Target-tracking scaling policies keep average CPU or request count near a goal, adding instances during spikes and removing them when idle. Instances and the database span multiple availability zones, so a zone failure does not take down the application. RDS Multi-AZ provides automatic database failover, and read replicas scale read-heavy workloads. CloudFront and ElastiCache reduce origin load. Health checks replace unhealthy instances automatically.
Security
The ALB terminates TLS 1.3 and sits in public subnets; instances and databases live in private subnets reachable only through the load balancer and NAT. Security groups enforce least-privilege network access between tiers. A WAF in front of CloudFront filters common attacks. IAM instance roles grant scoped access to S3 and other services without static keys. Secrets come from a managed secrets store, and the data tier is encrypted at rest.
Trade-offs and Alternatives
This architecture is simple, well understood, and cheap to operate, but you still manage operating systems, patching, and machine images. Scaling reacts to metrics, so very sudden spikes can briefly outpace it; pre-warming or over-provisioning helps. For higher density and faster deploys, containers on ECS or EKS are a natural next step; for spiky or low-traffic workloads, serverless avoids idle cost entirely. Choose the autoscaling web tier when you want a dependable, low-complexity platform for steady web traffic.