In practice the same software (Nginx, HAProxy, Traefik) can do both jobs. That is why the two terms are often confused. Conceptually, though, they solve different problems: a reverse proxy is an intermediary, a load balancer is a distributor.
The Conceptual Difference
Every load balancer can be a kind of reverse proxy, but not every reverse proxy is a load balancer. Nginx in front of a single server is not balancing load, but it is acting as a reverse proxy.
The Layer 4 vs Layer 7 Distinction
Layer 7 balancing reads the content: it can say send "/api" requests to this server and "/statik" requests to that one. Layer 4 is faster but unaware of content.
Load Distribution Algorithms
IP hash is used in applications that require session stickiness: the same user always goes to the same server, so session data does not have to be shared.
A Typical Architecture
In real systems the two work together. The layers are arranged like this:
| Layer | Component | Role |
|---|---|---|
| 1 | DNS / Anycast | Routes the user to the nearest region |
| 2 | CDN | Serves static content from the edge |
| 3 | Load balancer (L4) | Distributes traffic within the region |
| 4 | Reverse proxy (L7) | Terminates TLS, applies routing rules |
| 5 | Application servers | Do the actual work |
There is no forward proxy anywhere in this architecture — because it is at the other end of the chain, on the user's side. For the difference, see our forward and reverse proxy article in detail.
Health Checks
This is the clearest point at which a load balancer differs from a reverse proxy: it continuously monitors the health of the servers behind it and removes a faulty one from the pool.
This logic is exactly the same as the one in proxy pool management. In our pool article we described the client-side equivalent of the same pattern.
Why Does It Matter When Collecting Data?
The target site's load balancer may distribute your requests across different servers. This can lead to inconsistent results:
- Different versions: During a staged rollout, some servers may be running the new version.
- Session loss: Without session stickiness, your cookies may not be recognized on a different server.
- Variable response time: There may be performance differences between servers.
- A/B tests: Different requests may see different variants.
To reduce these inconsistencies, it helps to use a sticky session and to send consecutive requests from the same IP.
Summary
A reverse proxy is an intermediary that receives and forwards requests; a load balancer is a component that distributes those requests across multiple servers and monitors their health. The same software can take on both roles, which is why the terms get confused. Layer 4 balancing is fast but content-unaware, while layer 7 balancing is content-aware but more costly. When you collect data, these layers on the target's side can be the hidden cause of inconsistent results and dropped sessions.