CDN vs Reverse Proxy vs Load Balancer: What to Use When

Teams often blur the lines between a content delivery network, a reverse proxy, and a load balancer because all three sit “in the path” of requests and can speed things up or make things safer. But they solve different problems, live at different layers, and shine under different traffic and failure patterns. If you pick the wrong one first, you’ll either overpay for features you don’t use or ship an architecture that creaks the moment you see a traffic spike.

The short version: a CDN replicates or caches content near users to shrink latency and offload your origin; a reverse proxy is a smart doorman in front of one or more apps that can terminate TLS, rewrite requests, and shield origins; a load balancer spreads requests across multiple backends and detects when one is unhealthy, often at transport (L4) or application (L7) layer. You’ll usually combine them—CDN at the edge, reverse proxy and load balancer closer to your app—rather than pick exactly one.

Getting the boundaries right lets you answer practical questions with confidence: where to terminate TLS, which box adds headers like X-Forwarded-For, whether to cache or compute at the edge, and how to route by URL path or by TCP port. Below we compare their roles, limits, and common deployment patterns, then give you a simple decision checklist.

Understanding CDN, Reverse Proxy, and Load Balancer

A CDN is a distributed network of edge servers that caches static assets (and sometimes dynamic content) close to users so requests travel fewer network hops and origins serve fewer bytes. With caching, edge servers can serve images, scripts, and even whole HTML responses directly while your origin handles cache misses or purges. Most managed CDNs also provide global reach, edge TLS, HTTP/2 and HTTP/3 support, DDoS absorption, and request shielding in front of your origin.

A reverse proxy sits in front of your application servers and forwards client requests to them. Because it sees full HTTP traffic, it can terminate TLS, normalize and rewrite headers, compress responses, buffer or stream payloads, enforce access control, and centralize things like certificates and rate limits. Think of it as a programmable gateway where you codify policy for all inbound traffic before it touches your app.

A load balancer distributes traffic across multiple upstream targets. Health checks detect and bypass failed nodes. At L4, it balances raw TCP or UDP flows with very low overhead. At L7, it understands HTTP(S), can route by host or path, and supports cookie-based or header-based stickiness. Managed LBs from cloud providers offer zonal or regional high availability and automatic scaling of the balancing plane.

Primary Use Cases

Use a CDN when your bottleneck is distance or egress volume: public websites with many static assets, media delivery, API responses that benefit from short TTL caching, and download distribution. Use a reverse proxy to standardize cross-cutting web concerns: TLS offload, header-based auth, URL rewriting, response compression, or to hide private topology behind a single entry point. Use a load balancer when you need horizontal scale or fault isolation across multiple replicas, zones, or microservices, and you want automatic failover when a node turns unhealthy.

Key Differences That Matter Day to Day

State and cache: CDNs replicate and cache; load balancers do not. Protocol depth: L4 balancers move packets and are protocol-agnostic; L7 balancers and reverse proxies understand HTTP semantics. Policy surface: reverse proxies expose rich policy (rewrites, auth, content rules); L4 balancers expose simpler connection-level knobs. Topology: CDNs live globally at the edge; reverse proxies and LBs usually live in your VPC or data center.

Capabilities and Limits

Performance: CDNs cut latency by serving from a nearby edge and reduce origin CPU and bandwidth by caching. Reverse proxies improve perceived speed with keep-alive, connection pooling to origins, compression, and buffering for slow clients. Load balancers help capacity by fanning out requests across many replicas and by avoiding overloaded or failed nodes.

Security: CDNs front-run volumetric attacks at scale and can block abusive IPs or countries before traffic hits your network. Reverse proxies add TLS termination with modern ciphers, mutual TLS to origins, header normalization to defuse request smuggling, and IP/geo-based allowlists. Load balancers enforce basic network isolation and, at L7, can help with WAF integrations and per-route policies, but they’re not caching or full security layers by themselves.

Reliability: CDNs give you global points of presence and can keep serving cached content during short origin blips. Reverse proxies centralize fail-open/fail-closed behavior and can route around a failed origin pool. Load balancers are the workhorse for health checks and failover; they constantly probe targets and drain connections during deployments so users don’t see errors.

Routing and Session Affinity

Reverse proxies and L7 balancers both handle smart routing. Typical rules route by host header (multi-tenant apps), by URL path (microservices behind one domain), or by header/cookie (canary releases). Session stickiness is easy at L7 (via cookies, headers, or consistent hashing). If you need stickiness for non-HTTP protocols, pick L4 with source-IP hashing or an application-aware strategy higher up.

Observability and Control

All three surfaces produce logs and metrics, but with different scopes. CDNs expose edge hit/miss, cache status codes, and origin errors. Reverse proxies provide detailed request/response logs, upstream timings, and header views to debug policy and rewrites. Load balancers report target health, success rates, and latency percentiles per target group. Centralizing logs from edge, proxy, and LB gives you end-to-end timing to find where time is lost.

Common Deployment Patterns

Edge-first: Internet → CDN → Reverse Proxy (in your network) → App servers. This is the default for public sites: cache what you can at the edge, then apply policy and TLS/control at the proxy, and fan out to a pool via the proxy or a dedicated LB.

Split responsibility: Internet → CDN → L7 Load Balancer → Multiple services. Here the LB does host/path routing to service-specific pools. A lightweight reverse proxy may still sit in front of each service for service-specific logic.

Compute-heavy APIs: Internet → L4 Load Balancer → Reverse Proxy per service → App. If responses are mostly uncachable, you may not need a CDN; or you use the CDN for TLS and DDoS only with caching disabled.

Kubernetes: Internet → Cloud L4 LB → Ingress (reverse proxy) → Services/Pods. The cloud LB exposes a stable IP per cluster or per service; the ingress controller (a reverse proxy) applies HTTP routing and policy.

Blue/Green, Canary, and Failover

Weighted routing at the LB or reverse proxy lets you send a small slice of traffic to a new version, measure, and roll forward. Health checks pull a target out on 5xx spikes. For disaster recovery, keep a warm pool in a second zone or region and flip traffic with DNS or a global LB—just beware of TTLs and caches when you need fast flips.

Cost and Egress

CDNs reduce origin egress bill by serving cache hits at the edge, but you pay per GB at the edge plus request features. Reverse proxies are often inexpensive to run yourself but still consume egress from your network to users via your LB or ISP. Managed LBs charge per hour plus per LCU/NLCU or per-provisioned capacity. Model costs with realistic request mixes (cacheability %, average object size, TLS rates) before choosing.

Decision Guide

If you need global latency reduction or to offload bytes: start with a CDN. If you need HTTP policy, TLS offload, header rewrites, or a single public entry point for many internal services: add a reverse proxy. If you need scale-out and failover across multiple replicas: deploy a load balancer. In practice, most production stacks end up with all three; the trick is placing them so each does the minimum necessary work.

Practical Checklist

Define cacheability rules (what can be cached at edge, for how long, and how to purge), decide where TLS terminates (edge vs proxy vs app), choose LB layer (L4 for raw speed and non-HTTP protocols; L7 for HTTP routing and stickiness), wire health checks and timeouts, standardize headers (X-Forwarded-For, X-Forwarded-Proto, Forwarded), and set clear failure behavior (serve-stale at CDN, retry at proxy, drain at LB). Test with synthetic checks that exercise cache miss, cache hit, and origin fail cases.

Where Each Choice Breaks Down

CDNs don’t help much for highly personalized or long-poll streaming without special features; you may turn off caching and only use edge TLS and DDoS. Reverse proxies don’t replace horizontal scale and can become a bottleneck if you stuff all logic into them. Load balancers won’t compress, rewrite, or cache; they simply move traffic and detect health. Watch for single-box chokepoints and plan capacity and redundancy per layer.