Load balancing software spreads incoming traffic across several servers so that no single machine takes the whole load, and you can get it three ways. You can run an open source proxy yourself, buy a commercial application delivery controller, or switch on a managed service from your cloud provider.
The idea's older than most of the products. IETF RFC 1794, DNS Support for Load Balancing, came out in April 1995 and discusses using DNS to spread load across clusters of machines. That paper is about DNS and not about anything you'd buy today, but it makes a useful point: the concept was settled decades ago, so what you're choosing between now isn't the idea. It's who operates it, who you call at 3am, and how you get billed.
Open source proxies: free to run, yours to look after
Four of the nine sit in this group, and the table below marks them. None of them needs a sales call, and that's a real advantage when you want to try something tonight. The trade is that you operate them. You're installing, patching, watching and upgrading, so 'free' only describes the licence and not the hours.
These projects don't describe themselves the same way. HAProxy calls itself reliable and high performance. Traefik leans on easy and dynamic. Envoy's site now highlights load balancing tuned for AI inference traffic. Those are their own words, but they give you a decent clue about who each one's talking to.
Commercial ADCs: more in the box, more to buy
ADC stands for application delivery controller, and it's the category name for a balancer that's grown into something bigger. F5, NetScaler, A10 and Barracuda all bundle load balancing with security and support, which is the reason to buy one. If you want one company to ring when something breaks, this is the group that offers it.
The thing to test here is how much of that bundle you'd use. A bigger suite is only better value if you were going to need the security features anyway. If you already have a firewall and an application security tool you like, you may be buying the same protection twice. Ask each vendor to separate what's included from what's an add-on, and get it in writing.
Cloud managed: a line on your bill, not a product you install
AWS Elastic Load Balancing is the example on this list. There's nothing to install or patch, and it's charged by usage on your AWS bill. That's easy to start with, and it's why many teams never look further. The catch is that it only makes sense when your workload's already there. It also means the bill moves with your traffic, so look at the usage rates before a busy period and not after. If you're still picking somewhere to run things, our cloud server hosting list covers that first decision.
The balancing methods, in plain words
Whichever group you choose, you'll meet the same small set of methods. NGINX documents them clearly, and the descriptions below follow its docs:
- Round-robin: requests go to each server in turn. It's the default if you don't specify anything.
- Least-connected: the next request goes to the server with the fewest active connections, which helps when some requests take much longer than others.
- Least-time: picks the server with the lowest average response time and the lowest number of active connections.
- Weighted: you give some servers a bigger share by setting server weights, handy when your machines aren't the same size.
Its docs also describe passive health checks: if a server's response fails with an error, that server gets marked as failed for a while. Ask any vendor how theirs behaves when a server goes bad, because that's the moment you're paying for all this.
All nine at a glance
Listed alphabetically, in no particular order of merit.
| Tool | Group | How the vendor puts it |
|---|---|---|
| A10 Thunder ADC | Commercial ADC | Application delivery and load balancing |
| AWS Elastic Load Balancing | Cloud managed | Load balancing inside AWS, charged by usage |
| Barracuda Load Balancer | Commercial ADC | Load balancer sold as part of application protection |
| Envoy | Open source proxy | Open source proxy with load balancing |
| F5 BIG-IP | Commercial ADC | Security, availability and performance across hybrid and multi-cloud |
| HAProxy | Open source proxy | TCP and HTTP load balancer |
| NetScaler | Commercial ADC | Application delivery and security |
| NGINX | Open source proxy | Documents round-robin, least-connected, least-time and weighted balancing |
| Traefik | Open source proxy | Reverse proxy and load balancer for HTTP and TCP |
A10 Thunder ADC
Best for: Teams shopping for a dedicated application delivery controller; the vendor claims high-performance load balancing for application availability.
AWS Elastic Load Balancing
Best for: Workloads already running on AWS, where it's a managed service charged by usage on your AWS bill.
Barracuda Load Balancer
Best for: Buyers who want balancing and application protection from one vendor, since it's sold with security features.
Envoy
Best for: Platform engineers running AI services, as its site highlights load balancing tuned for AI inference traffic (a project claim).
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F5 BIG-IP
Best for: Large estates across hybrid and multi-cloud, sold as a family of application services and not a single box, the vendor says.
HAProxy
Best for: Operators wanting a dedicated TCP and HTTP balancer they run themselves; it calls itself reliable and high performance.
NetScaler
Best for: Enterprises wanting application delivery and security together; the vendor says the world's largest companies prefer it, so ask for references.
NGINX
Best for: Readers who like clear documentation, because its own docs set out each balancing method alongside health checks.
Traefik
Best for: Small platform teams; it describes itself as easy, dynamic and full-featured, and works as a reverse proxy for HTTP and TCP.
Short advice on where to begin
If you've got engineers who enjoy this sort of thing and you want control, start with an open source proxy. If you're already all-in on one cloud and just want traffic spread with the least fuss, use the managed balancer you've already got and don't overthink it. If you're a larger business with compliance people and a need for someone to call, that's when a commercial ADC earns its place. Don't buy one because it feels safer, though. Buy it because you can name the features you'd use.
And if what you're after is routing and managing API traffic and not only spreading load, have a look at our API gateways list. Those tools overlap with some proxies here, but they're solving a different problem.
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Quick answers on load balancers
What's the difference between a load balancer and an ADC?
A load balancer spreads traffic across servers. An application delivery controller does that too and adds more on top, usually security and other application services, with vendor support behind it.
Is open source load balancing software free?
The software's free to run, but you still operate it. Installing, patching and monitoring all take time, so count those hours when you compare it with a managed service or a commercial product.
Which balancing method should I start with?
Round-robin is the simple starting point, and it's fine when your servers are alike and requests are short. Move to least-connected when some requests take far longer than others.
