CloudFront vs Global Accelerator: CDN Caching vs TCP/UDP Network Optimisation

AWS has two services that both promise to make applications faster for users around the world. From the outside they look similar — both use AWS edge infrastructure, both reduce latency, both have global presence. In practice they solve completely different problems, and choosing the wrong one either adds unnecessary cost or fails to fix the actual performance issue.

The Core Difference

CloudFront is a Content Delivery Network. It caches responses at edge locations. When a user requests a file and it is already cached at the nearest edge, CloudFront returns it immediately without contacting the origin server. The speed improvement comes from serving data from a location geographically close to the user.

AWS Global Accelerator is a network routing service. It does not cache content. Instead, it routes TCP and UDP traffic over the AWS global network (private backbone fibre) from the nearest edge to the endpoint in an AWS region. The speed improvement comes from avoiding the unpredictable public internet for long-haul routing.

CloudFront:
  User --> Edge Location --> Cache HIT: serve locally (no origin contact)
                         --> Cache MISS: fetch from origin, cache, serve

Global Accelerator:
  User --> Edge Location (receives connection) --> AWS backbone --> Regional endpoint
  (no caching — every request goes to the regional endpoint,
   just via a faster, more reliable network path)

What CloudFront Is Good At

CloudFront excels when the content itself can be cached. This includes:

• Static assets: images, CSS, JavaScript, fonts, video files
• HTML pages that change infrequently
• API responses that are the same for many users (public data feeds, catalogue data)
• Software downloads and firmware updates

The key question: “Would two different users asking for the same URL get the same response?” If yes, CloudFront can cache it and serve both from the same cache entry.

CloudFront also handles:

• TLS termination at the edge (HTTPS to origin can use HTTP internally to reduce TLS overhead)
• Geo-restriction (block requests from specific countries)
• WAF integration for edge-based filtering
• Lambda@Edge for request/response manipulation
• Signed URLs for access control

What Global Accelerator Is Good At

Global Accelerator improves performance for use cases where caching is not applicable:

• Highly dynamic applications: Each user request is unique (REST API calls, financial transactions, user-specific data)
• Non-HTTP protocols: UDP-based gaming, VoIP, real-time communications, gRPC
• TCP applications where connection stability matters: Long-lived TCP connections, WebSocket sessions
• Multi-region active-active architectures: Route users to the nearest healthy region with automatic failover

Global Accelerator uses Anycast IP addresses — two static IPs that are advertised from all edge locations simultaneously. Users connect to the same IP address regardless of location, and BGP routing directs them to the nearest edge. From the edge, traffic travels the AWS backbone to the designated region.

Global Accelerator Network Flow:

User in Tokyo
     |
     | Connects to: 75.2.68.225 (static Anycast IP)
     v
[Edge Location: Tokyo] <-- closest to user
     |
     | AWS backbone (private, predictable, low jitter)
     v
[ALB in ap-northeast-1] OR [ALB in us-east-1]
     | (traffic sent to nearest healthy endpoint)
     v
Application servers

The static Anycast IPs are a practical advantage for clients that need to whitelist IP addresses in firewalls or security groups. CloudFront’s edge IPs change over time; Global Accelerator’s two IPs are permanent.

Head-to-Head Comparison

When the Choice Is Obvious

Clearly CloudFront:

• You are serving a marketing website with images and CSS
• You are distributing a software package for global download
• You have API responses that can be cached for 60 seconds
• You want to add a WAF in front of your application

Clearly Global Accelerator:

• You are running a multiplayer game that uses UDP
• You have a financial trading application where each transaction is unique and latency variance (jitter) matters
• You are running two application regions in active-active mode and need automatic failover
• Your enterprise clients require whitelisting static IP addresses for firewall rules

When You Might Use Both

CloudFront and Global Accelerator solve different layers of the same performance problem, and some architectures use both.

Example: A global SaaS application with both static assets and a dynamic API

Static assets (JS, CSS, images):
  User --> CloudFront --> S3
  (cached at edge, served in milliseconds)

Dynamic API (user-specific data, transactions):
  User --> Global Accelerator --> Regional ALB --> App servers
  (routed over AWS backbone, no caching, always hits app)

The frontend static assets go through CloudFront. The API traffic goes through Global Accelerator. Users get fast initial page loads (CloudFront cache hits) and low-latency API responses (Global Accelerator backbone routing).

Cost Comparison

CloudFront charges for:

• Data transferred to users (per GB, varies by region)
• HTTP/HTTPS request count (per 10,000 requests)
• Lambda@Edge invocations if used

Global Accelerator charges:

• Fixed hourly rate per accelerator ($0.025/hour ≈$18/month)
• Data transfer premium (typically $0.015/GB above standard transfer rates, varies by region)

For applications with very high request volumes and highly cacheable content, CloudFront is almost always cheaper because cached responses dramatically reduce the effective data transfer and origin requests. Global Accelerator’s fixed rate makes it predictable regardless of traffic volume.

Real-World Scenarios

Scenario 1: E-commerce product catalogue Thousands of product images and a public API for searching products by category. Both are the same for all users.

• Choose CloudFront: Cache product images and search API responses at edge. Cache hit rate of 80%+ after warm-up. Origin traffic drops to a fraction. Monthly cost: primarily data transfer.

Scenario 2: Online multiplayer game Real-time game state updates between players and game servers using UDP. Game state is per-session and unique.

• Choose Global Accelerator: No caching is possible. Route UDP traffic over AWS backbone to the nearest game server region. Reduce jitter for better gameplay experience.

Scenario 3: Global SaaS with active-active regions Application is deployed in us-east-1 and eu-west-1. Users should connect to the nearest healthy region. If one region fails, traffic should automatically shift.

• Choose Global Accelerator: Health check-based routing with automatic failover. Two static IPs for firewall whitelisting. CloudFront would not help here because the content is dynamic and region affinity matters.

Interview Notes

Q: Can Global Accelerator improve performance for HTTP applications? Yes. Even for HTTP applications, Global Accelerator reduces latency because traffic is routed over the AWS backbone rather than the public internet. The improvement over CloudFront is most noticeable for dynamic, non-cacheable content — for static or cacheable content, CloudFront’s edge cache is typically faster and cheaper.

Q: What are Anycast IPs, and why does Global Accelerator use them? Anycast is a network addressing scheme where the same IP address is announced from multiple locations. BGP routing directs traffic to the nearest location announcing that address. Global Accelerator uses two Anycast IPs that are advertised from all AWS edge locations. Users always connect to the same IPs; the network automatically routes them to the nearest edge.

Q: Does Global Accelerator work with on-premises servers? Yes. You can add on-premises server endpoints to a Global Accelerator. Traffic travels the AWS backbone from the nearest edge to an AWS region, then exits to your on-premises server via Direct Connect or VPN. This gives public internet users the backbone routing benefit even for hybrid architectures.