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HAProxy is free, open source software that provides a high availability load balancer and proxy server for TCP and HTTP-based applications that spreads requests across multiple servers. It is written in C and has a reputation for being fast and efficient (in terms of processor and memory usage).


Automatically ban offending traffic

Check these two posts:

Configure haproxy logs to be sent to loki

In the fronted config add the next line:

  # For more options look at
  log-format 'client_ip=%ci client_port=%cp frontend_name=%f backend_name=%b server_name=%s performance_metrics=%TR/%Tw/%Tc/%Tr/%Ta status_code=%ST bytes_read=%B termination_state=%tsc haproxy_metrics=%ac/%fc/%bc/%sc/%rc srv_queue=%sq  backend_queue=%bq user_agent=%{+Q}[capture.req.hdr(0)] http_hostname=%{+Q}[capture.req.hdr(1)] http_version=%HV http_method=%HM http_request_uri="%HU"'

At the bottom of chrisk post is a table with all the available fields.

Programming VIP also has an interesting post.

Use HAProxy as a reverse proxy

reverse proxy is a type of proxy server that retrieves resources on behalf of a client from one or more servers. These resources are then returned to the client, appearing as if they originated from the server itself. Unlike a forward proxy, which is an intermediary for its associated clients to contact any server, a reverse proxy is an intermediary for its associated servers to be contacted by any client. In other words, a proxy is associated with the client(s), while a reverse proxy is associated with the server(s); a reverse proxy is usually an internal-facing proxy used as a 'front-end' to control and protect access to a server on a private network.

It can be done at Web server level (Nginx, Apache, ...) or at load balancer level.

This HAProxy post shows how to translate Apache's proxy pass directives to the HAProxy configuration.

    frontend ft_global
     acl    req.hdr(Host)
     acl path_mirror_foo path -m beg   /mirror/foo/
     use_backend bk_myapp if path_mirror_foo
    backend bk_myapp
    # external URL                  => internal URL
    # =>
     # ProxyPass /mirror/foo/
     http-request set-header Host
     reqirep  ^([^ :]*)\ /mirror/foo/(.*)     \1\ /\2
     # ProxyPassReverse /mirror/foo/
     # Note: we turn the urls into absolute in the mean time
     acl hdr_location res.hdr(Location) -m found
     rspirep ^Location:\ (https?://[0-9]+)?)?(/.*) Location:\ /mirror/foo3 if hdr_location
     # ProxyPassReverseCookieDomain
     acl hdr_set_cookie_dom res.hdr(Set-cookie) -m sub Domain=
     rspirep ^(Set-Cookie:.*)\*) \1\\2 if hdr_set_cookie_dom
     # ProxyPassReverseCookieDomain / /mirror/foo/
     acl hdr_set_cookie_path res.hdr(Set-cookie) -m sub Path=
     rspirep ^(Set-Cookie:.*)\ Path=(.*) \1\ Path=/mirror/foo2 if hdr_set_cookie_path

Other useful examples can be retrieved from drmalex07 or ferdinandosimonetti gists.


Reload haproxy

  • Check the config is alright
    service haproxy configtest
    # Or
    /usr/sbin/haproxy -c -V -f /etc/haproxy/haproxy.cfg
  • Reload the service
    service haproxy reload

If you want to do a better reload you can drop the SYN before a restart, so that clients will resend this SYN until it reaches the new process.

iptables -I INPUT -p tcp --dport 80,443 --syn -j DROP
sleep 1
service haproxy reload
iptables -D INPUT -p tcp --dport 80,443 --syn -j DROP
service haproxy reload

Comparison between haproxy and varnish

In the opensource world, there are some very smart products which are very often used to build a high performance, reliable and scalable architecture.\ HAProxy and Varnish are both in this category.

Since we can’t really compare a reverse-proxy cache and a reverse-proxy load-balancer, I’m just going to focus in common for both software as well as the advantage of each of them.\ The list is not exhaustive, but must only focus on most used / interesting features. So feel free to add a comment if you want me to complete the list.

Common points between HAProxy and Varnish

Before comparing the differences, we can summarize the points in common: * Reverse-proxy mode * Advanced HTTP features * No SSL offloading * Client-side HTTP 1.1 with keepalive * Tunnel mode available * High performance * Basic load-balancing * Server health checking * IPv6 ready * Management socket (CLI) * Professional services and training available

Features available in HAProxy and not in Varnish

The features below are available in HAProxy, but aren’t in Varnish: * Advanced load-balancer * Multiple persistence methods * DOS and DDOS mitigation * advanced and custom logging * web interface * server / application protection through queue management, slow start, etc… * sNI content switching * Named ACLs * Full HTTP 1.1 support on server side, but keep-alive * Can work at TCP level with any L7 protocol * Proxy protocol for both client and server * Powerful log analyzer tool (halog) * <private joke> 2002 website design </private joke>

Features available in Varnish and not in HAProxy

The features below are available in Varnish, but aren’t in HAProxy: * Caching * Grace mode (stale content delivery) * Saint mode (manages origin server errors) * Modular software (with a lot of modules available) * Intuitive VCL configuration language * HTTP 1.1 on server side * TCP connection re-use * Edge side includes (ESI) * A few command line tools for stats (varnishstat, varnishhist, etc…) * Powerful live traffic analyzer (varnishlog) * <private joke> 2012 website design </private joke>


Even if HAProxy can do TCP proxying, it is often used in front of web application, exactly where we find Varnish :).\ They complete very well together: Varnish will make the website faster by offloading static object delivery to itself, while HAProxy can ensure a smooth load-balancing with smart persistence and DDOS mitigation. Basically, HAProxy and Varnish completes very well, despite being “competitors” on a few features, each on them has its own domain of expertise where it performs very well: HAProxy is a reverse-proxy Load-Balancer and Varnish is a Reverse-proxy cache.

To be honest, when, at HAProxy Technologies, we work on infrastructures where Aloha Load balancer or HAProxy is deployed, we often see Varnish deployed. And if it is not the case, we often recommend the customer to deploy one if we feel it would improve its website performance.\ Recently, I had a discussion with Ruben and Kristian when they came to Paris and they told me that they also often see an HAProxy when they work on infrastructure where Varnish is deployed.

So the real question is: Since Varnish and HAProxy are a bit similar but complete so well, how can we use them together???\ The response could be very long, so stay tuned, I’ll try to answer this question in an article coming soon.

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