Résultats de la recherche

Mot clé : ‘HAProxy’

Installing A High Availability Web Server Cluster On Ubuntu 12.10 Using HAProxy, HeartBeat And Lampp

13/05/2024 Aucun commentaire

What is the main objective of this entire topology?

high availability web server clusterRedundancy and Load Sharing! Imagine a scenario where your single web server is receiving millions and millions of HTTP requests per second, the CPU load is going insane, as well as the memory usage, when suddenly “crash!”, the server dies without saying good-bye (probably because of some weird hardware out-stage that you certainly won’t have time to debug). Well, this simple scheme might lead you into a brand new world of possibilities

What is this going to solve?

Hardware Failures! We are going to have redundant hardware all over the place, if one goes down, another one will be immediately ready for taking its place. Also, by using load sharing schemes, this is going to solve our High Usage! issue. Balancing the load among every server on our “farm” will reduce the amount of HTTP request per server (but you already figured that out, right?).
Let’s set it up! Firstly, we’re not going to use a domain scheme (let’s keep it simple), make sure your /etc/hosts file looks exactly like the picture below on every machine:
#vi /etc/hosts   haproxy Node1 Node2 Node1 Node2 Web1 Web2 Mysql

Lire la suite…

Categories: Système Tags: ,

Installing a high availability web server cluster on Ubuntu 12.04 LTS using HAProxy, HeartBeat and Nginx

12/05/2024 Comments off

How to set-up a high-availability cluster

Here are a few notes about how to set-up a high-availability web server farm using Ubuntu 12.04 LTS using a whole load of awesome software (HAProxy, HeartBeat, Watchdog and Nginx)

The setup

In my setup I have five virtual machines, these are named and used for the following:-

haproxy1 – Our first proxy (master)/load-balancer (running HAProxy, HeartBeat and Watchdog) [IP address:]
haproxy2 – Our second proxy (failover)/load-balancer (running HAProxy, HeartBeat and Watchdog) [IP address:]
web1 – Our first web server node (running nginx) [IP address:]
web2 – Our second web server node (running nginx) [IP address:]
web3 – Our third web server node (running nginx) [IP address:]

The servers are connected in the following way:-


In my next post I will also explain how to configure the web servers to point to a backend shared storage cluster (using NFS) and a MySQL cluster server to have a truly highly available web hosting platform.

Lire la suite…

Stop DDoS attack with iptables

15/05/2024 Aucun commentaire

stop ddos attack iptablesIn fight against DDoS through the years, i’ve compiled a list of useful iptables commands which may come handy in time of trouble.

Here is how to stop DDoS attack with iptables

To block small SYN floods:
iptables -A INPUT -p tcp --syn -m limit --limit 1/s --limit-burst 3 -j RETURN

To block small UDP floods:
iptables -N udp-flood
iptables -A OUTPUT -p udp -j udp-flood
iptables -A udp-flood -p udp -m limit --limit 50/s -j RETURN
iptables -A udp-flood -j LOG --log-level 4 --log-prefix 'UDP-flood attempt: '
iptables -A udp-flood -j DROP

To limit rate of connections on a port:
iptables -A INPUT -p tcp --dport (port-here) -m state --state NEW -m recent --set --name DDOS --rsource
iptables -A INPUT -p tcp --dport (port-here) -m state --state NEW -m recent --update --seconds 5 --hitcount 5 --name DDOS --rsource -j DROP

Limit connections per ip on a port
iptables -A INPUT -p tcp --syn --dport (port-here) -m connlimit --connlimit-above (limit-here) --connlimit-mask 32 -j REJECT --reject-with tcp-reset

To block an ip using iptables
iptables -A INPUT -s (ip-here) -j DROP

If you use haproxy as load balancer use this to limit concurrent connections:
stick-table type ip size 200k expire 30s store conn_cur
tcp-request connection reject if { src_conn_cur ge 6 }
tcp-request connection track-sc1 src

iptables man page
Haproxy website

Source: Stickpoll

Use a load-balancer as a first row of defense against DDoS

14/05/2024 Aucun commentaire

Source: haproxy.com

We’ve seen recently more and more DOS and DDoS attacks. Some of them were very big, requiring thousands of computers…
But in most cases, this kind of attacks are made by a few computers aiming to make a service or website unavailable, either by sending it too many requests or by taking all its available resources, preventing regular users to use the service.
Some attacks targets known vulnerabilities of widely used applications.

In the present article, we’ll explain how to take advantage of an application delivery controller to protect your website and application against DoS, DDoS and vulnerability scans.

Why using a LB for such protection since a firewall and a Web Application Firewall (aka WAF) could already do the job?
Well, the Firewall is not aware of the application layer but would be useful to pretect against SYN flood attacks. That’s why we saw recently application layer firewalls: Web Application Firewalls, also known as WAF.
Well, since the load balancer is in front of the platform, it can be a good partner for the WAF, filtering out 99% of the attacks, which are managed by script kiddies. The WAF can then happily clean up the remaining attacks.
Well, maybe you don’t need a WAF and you want to take advantage of your Aloha and save some money ;).

Note that you need an application layer load-balancer, like Aloha or OpenSource HAProxy to be efficient.

TCP syn flood attacks

The syn flood attacks consist in sending as many TCP syn packets as possible to a single server trying to saturate it or at least, saturating its uplink bandwith.

If you’re using the Aloha load-balancer, you’re already protected against this kind of attacks: the Aloha includes mechanism to protect you.
The TCP syn flood attack mitigation capacity may vary depending on your Aloha box.

It you’re running your own LB based on HAProxy or HAPEE, you should have a look at the sysctl below (edit /etc/sysctl.conf or play with sysctl command):

# Protection SYN flood
 net.ipv4.tcp_syncookies = 1
 net.ipv4.conf.all.rp_filter = 1
 net.ipv4.tcp_max_syn_backlog = 1024

Note: If the attack is very big and saturates your internet bandwith, the only solution is to ask your internet access provider to null route the attackers IPs on its core network.

Lire la suite…

How To Optimize WordPress Performance With MySQL Replication On Ubuntu 14.04

10/05/2024 Aucun commentaire


In this tutorial, we will teach you how to scale up your WordPress MySQL database server setup using master-slave database replication and the HyperDB plugin for WordPress. Adding more database servers to your environment in this manner allows your WordPress application to read from multiple database servers, increasing read performance.

MySQL replication reaps the most performance benefits for a system that processes frequent reads and infrequent writes, like most WordPress installations. By using a single-master with multiple-slave setup, you can add more slaves to scale your system, until you run out of network bandwidth or your master cannot handle the update load. If you wish, you can add more than one slaves by repeating the « slave » portions of the replication sections of this tutorial.

We are assuming that your setup includes two load balanced WordPress application servers that connect to a separate MySQL database server (see the prerequisites for a tutorial on how to set that up). It is not strictly necessary to have load balanced application servers to follow this tutorial, but your MySQL database server should be separate from your application servers.


Before continuing with this tutorial, you should have completed two tutorials or have a similar environment:

After following those tutorials, to set up WordPress with two load balanced web application servers and a separate database server, you should have four VPSs. Because we will be dealing with several VPSs, for reference purposes, we will call your four existing VPSs the following:

  • haproxy-www: Your HAProxy server for layer 4 load balancing your WordPress web application servers. This is the entry point into your website
  • wordpress-1: Your first WordPress web application server
  • wordpress-2: Your second WordPress web application server
  • mysql-1: Your MySQL server for WordPress

That is, your environment should look something like this:

WordPress and Separate MySQL Database Server

In addition to your current environment, we will require one additional VPS during this tutorial. We will call it:

  • mysql-2: Your slave MySQL database server

Lire la suite…