Java – What are the possible causes for Layer 4 and Layer 7 timeouts in HAProxy

Your confusion is reasonable - they are often the same thing. But not always. When you refer to a load balancer you are referring to a very specific thing - a server or device that balances inbound requests across two or more web servers to spread the load. A reverse proxy, however, typically has any number of features:

1. load balancing: as discussed above

2. caching: it can cache content from the web server(s) behind it and thereby reduce the load on the web server(s) and return some static content back to the requester without having to get the data from the web server(s)

3. security: it can protect the web server(s) by preventing direct access from the internet; it might do this through simple means by just obfuscating the web server(s) or it may have some more active components that actually review inbound requests looking for malicious code

4. SSL acceleration: when SSL is used; it may serve as a termination point for those SSL sessions so that the workload of dealing with the encryption is offloaded from the web server(s)

I think this covers most of it but there are probably a few other features I've missed. Certainly it isn't uncommon to see a device or piece of software marketed as a load balancer/reverse proxy because the features are so commonly bundled together.

2019 update:

They are both stable and mature products. HAProxy is dedicated to load balancing and is better at that, whereas nginx is a webserver that can act as a load balancer.

Both:

• HTTPS support
• Websocket support
• Stable, mature and very efficient products
• Can handle 10k connections with minimal or no tuning

HAProxy:

• TCP, TCP-SSL, HTTP and HTTPS load balancing
• More flexibility on health checks and failover conditions
• Basic caching (v1.8 - 2017)
• Customizable log format, to import access logs to kibana/splunk/graylog
• Detailed status page, to see active requests and servers status
• Exportable metrics, to integrate with monitoring solutions (graphite/prometheus/datadog)
• More high-performance oriented. Better indicated to handle 100k connections or 40 GbE interfaces.

Nginx:

• HTTP and HTTPS load balancing (TCP - UDP in paid edition)
• More flexibility on caching
• Customizable log format, to import access logs to kibana/splunk/graylog
• No status page (paid edition only)
• No exportable metrics (paid edition only)
• Can serve local files
• Can serve FastCGI applications (not CGI)

HAProxy is a free software, fully open source. They make money by selling hardware appliance with HAProxy pre-installed.

Nginx is open core and many features are only available in the paid edition. Notably, it's lacking a status page and monitoring metrics that is a big NO NO to operate a load balancer.