HAProxy, or High Availability Proxy, is a popular load balancer for web applications. It’s optimized to perform well under high traffic, both on-premise and in the cloud. It’s scalable and secure by design, ships with major Linux distributions, and supports HTTP/3 over QUIC.
HAProxy is integral to routing TCP/HTTP requests in a distributed architecture. To avoid performance bottlenecks in the overall system, monitoring HAProxy is essential. In this article, we share a comprehensive guide to HAProxy monitoring. We’ll explain its architecture, briefly compare it with Nginx, elaborate why monitoring is essential, and discuss how to monitor key metrics using native tools.
HAProxy is an open-source TCP/HTTP load balancer and reverse proxy. It’s widely used to distribute traffic across multiple servers based on predefined rules and algorithms. This load distribution increases the availability, reliability, and throughput of applications.
HAProxy supports Layer 4 (TCP) and Layer 7 (HTTP) load balancing. It works well with WebSocket and gRPC. It can be used to implement various routing features, such as URL rewriting, IP address load balancing, path-based writing, and rate limiting.
HAProxy also provides SSL termination out-of-the-box, a feature that encrypts/decrypts traffic at the load balancing layer. SSL termination protects against cyberattacks without adding any encryption/decryption overhead to the applications.
You can integrate HAProxy with many third-party applications to extend its capabilities. For example, HAProxy can be natively integrated with NS1, a DNS platform. Since it’s open-source, you can add custom functionality using the Lua scripting language.
HAProxy is used for wide-ranging use cases, including e-commerce, gaming, social media, and streaming services. In e-commerce, for example, HAProxy is deployed as a scalable load balancer to handle high volumes of requests during peak shopping periods. In gaming and streaming, it reduces latency by routing traffic to the nearest server or data center.
HAProxy is known to deliver exceptional performance, reliability, and availability. As per the official website, HAProxy can handle up to 2 million requests over SSL and 100 Gbps of forwarded traffic. These impressive figures can be attributed to its flexible, event-driven architecture.
HAProxy is a non-blocking engine that enables concurrent processing of incoming traffic through a fast I/O layer and a multi-threaded, priority-based scheduler. As its primary objective is forwarding requests to application servers, HAProxy is designed to move data with minimal processing.
A typical HAProxy-powered architecture comprises a frontend and a backend. The frontend contains listening sockets that accept incoming requests from clients. The backend defines a group of application servers that will be assigned requests by the frontend. Decoupling the frontend and backend layers also makes it possible to scale each independently.
Multi-threading allows HAProxy to leverage the maximum computational capacity by binding threads to CPU cores and decreasing the need for inter-CPU communication. HAProxy also uses a cache to store responses in RAM, which ensures that subsequent requests for the cached object aren’t forwarded to the backend.
HAProxy and Nginx are both excellent options for load balancing and reverse proxies. However, there are certain differences between the two solutions that may make you choose one over the other.
Nginx is more than just a load balancer or a reverse proxy. It can also be used as a standalone web server for delivering static or dynamic content. Conversely, HAProxy is predominantly a request-forwarder and can’t be used to serve static or dynamic content.
HAProxy offers a wider range of load balancing algorithms, including least connections, source IP hash, URI hash, header-based, and weighted round robin. Both solutions allow you to enforce rate limiting and SSL termination. However, Nginx offers generic UDP load balancing support, whereas HAProxy doesn’t.
Both web technologies do equally well in the configurability, performance, availability, and security departments. Whether you want to define access control lists (ACLs), increase threads for better throughput, or deploy across cloud and on-premise environments, both Nginx and HAProxy allow you to do so.
To summarize, there is no clear winner in the battle between HAProxy and Nginx. Which one you choose depends on your business use case and protocol requirements. For example, if you need both UDP and TCP load balancing, consider Nginx. If you want to use a specialized routing scheme, HAProxy may be a better choice.
Here are a few reasons why it’s essential to monitor the health and performance of HAProxy:
Periodic monitoring will equip you with the insight necessary to predict malfunctions. For example, if you notice a spike in the memory usage of an instance, you can investigate and take remedial action before HAProxy runs out of memory and crashes.
Monitoring can also help identify misconfigurations. For instance, if you increase the number of threads and notice that CPU and memory utilization rise without improving overall throughput, it's a sign that the thread count was set too high.
When it comes to a complicated, multi-layered system like HAProxy, troubleshooting can prove challenging in the absence of logs and monitoring tools. However, by cross-referencing logged events with crucial metrics, one can contextualize issues quicker.
For example, if the frontend queue depth increases exponentially along with backend latency, it suggests that the application servers are slowing down. Similarly, if a node crashes and the monitoring tool reports high memory usage on the backend, it’s likely that your application logic has memory leaks.
HAProxy serves as the backbone of numerous distributed IT infrastructures, enabling a cluster of application servers to cater to thousands of clients simultaneously. Even minor problems or bottlenecks in HAProxy can significantly impair the overall infrastructure's performance.
For instance, if a listening socket hangs due to overuse, clients may be unable to access their data from the website. It’s therefore crucial to monitor HAProxy’s scalability, performance, and health metrics in the context of the larger system.
Regular monitoring enables the identification of potential security incidents, bugs, or vulnerabilities. For instance, if any security-critical action is performed, or a security control is disabled, the monitoring tool may issue an alert.
Additionally, monitoring allows you to verify the adherence of security best practices across all areas, such as SSL/TLS encryption, rate limiting, access control lists, client fingerprinting, and packet analysis.
HAProxy exposes a range of metrics to monitor the status, performance, and throughput of the frontend, backend, and overall system. These metrics can also be exported as a comma-separated values (CSV) file.
Frontend is the entry point for all requests. Frontend metrics, like the following, clearly show how well an instance handles client connections.
The backend represents the request processing layer of HAProxy. Use the following backend-specific metrics to gauge performance and throughput of your application servers.
Monitoring the following metrics will give you an idea of the overall system’s health, availability, and performance.
HAProxy offers a built-in web-based dashboard, known as the HAProxy Stats page, which displays several key metrics. By default, this dashboard is disabled. To enable it, add the following lines of code to your haproxy.cfg file.
bind :9001 # Listening port. A different port can also be used.
stats enable # This enables the stats page
stats realm Haproxy\ Statistics # A custom title for the stats window
stats uri /stats # A custom URI for the stats page
stats auth Username:Password # Login credentials
Remember to set your own username and password in the last line. After you have done that, restart the HAProxy service. Then you will be able to log into the stats page at: http://[HAProxy-IP]:9001/stats using the defined login credentials.
An alternative way to access the stats is via a UNIX socket interface. To enable the socket interface, add the following line to your haproxy.cfg file, under global settings:
stats socket /run/haproxy/haproxy.sock mode 660 level admin
The HAProxy monitoring plugin offered by Site24x7 is a great tool to monitor HAProxy in real time. The Python-based plugin can be downloaded from GitHub and installed in a few simple steps. You can also visualize the metrics this plugin aggregates on the Site24x7 web client.
Some of the performance metrics you can track using the plugin include:
HAProxy is a leading load balancer and reverse proxy for TCP/HTTP applications. It supports advanced load balancing schemes, scales well in the cloud, offers a diverse routing feature set, and is highly extensible. To maximize its potential, use the information in this article to identify the metrics and tools that are best suited for you to monitor it closely.
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