Archives pour 09/2020

How To Set Up an Iptables Firewall to Protect Traffic Between your Servers

30/09/2020 Comments off

Source DigitalOcean – Justin Ellingwood


Deploying discrete components in your application setup onto different nodes is a common way to decrease load and begin scaling horizontally. A typical example is configuring a database on a separate server from your application. While there are a great number of advantages with this setup, connecting over a network involves a new set of security concerns.

In this guide, we’ll demonstrate how to set up a simple firewall on each of your servers in a distributed setup. We will configure our policy to allow legitimate traffic between our components while denying other traffic.

For the demonstration in this guide, we’ll be using two Ubuntu 14.04 servers. One will have a WordPress instance served with Nginx and the other will host the MySQL database for the application. Although we will be using this setup as an example, you should be able to extrapolate the techniques involved to fit your own server requirements.


To get started, you will have to have two fresh Ubuntu 14.04 servers. Add a regular user account with sudo privileges on each. To learn how to do this correctly, follow our Ubuntu 14.04 initial server setup guide.

The application setup we will be securing is based on this guide. If you’d like to follow along, set up your application and database servers as indicated by that tutorial.

Setting Up a Basic Firewall

We will begin by implementing a baseline firewall configuration for each of our servers. The policy that we will be implementing takes a security-first approach. We will be locking down almost everything other than SSH traffic and then poking holes in the firewall for our specific application.

The firewall in this guide provides the basic setup that we need. Install the iptables-persistent package and paste the basic rules into the /etc/iptables/rules.v4 file:

sudo apt-get update
sudo apt-get install iptables-persistent
sudo nano /etc/iptables/rules.v4
# Allow all outgoing, but drop incoming and forwarding packets by default

# Custom per-protocol chains
:UDP - [0:0]
:TCP - [0:0]
:ICMP - [0:0]

# Acceptable UDP traffic

# Acceptable TCP traffic
-A TCP -p tcp --dport 22 -j ACCEPT

# Acceptable ICMP traffic

# Boilerplate acceptance policy
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
-A INPUT -i lo -j ACCEPT

# Drop invalid packets
-A INPUT -m conntrack --ctstate INVALID -j DROP

# Pass traffic to protocol-specific chains
## Only allow new connections (established and related should already be handled)
## For TCP, additionally only allow new SYN packets since that is the only valid
## method for establishing a new TCP connection
-A INPUT -p udp -m conntrack --ctstate NEW -j UDP
-A INPUT -p tcp --syn -m conntrack --ctstate NEW -j TCP
-A INPUT -p icmp -m conntrack --ctstate NEW -j ICMP

# Reject anything that's fallen through to this point
## Try to be protocol-specific w/ rejection message
-A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable
-A INPUT -p tcp -j REJECT --reject-with tcp-reset
-A INPUT -j REJECT --reject-with icmp-proto-unreachable

# Commit the changes





If you are implementing this in a live environment do not reload your firewall rules yet. Loading the basic rule set outlined here will immediately drop the connection between your application and database server. We will need to adjust the rules to reflect our operational needs before reloading.

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How To Migrate Iptables Firewall Rules to a New Server

30/09/2020 Comments off

Source: DigitalOcean – Mitchell Anicas


When migrating from one server to another, it is often desirable to migrate the iptables firewall rules as part of the process. This tutorial will show you how to easily copy your active iptables rule set from one server to another.


This tutorial requires two servers. We will refer to the source server, which has the existing iptables rules, as Server A. The destination server, where the rules will be migrated to, will be referred to as Server B.

You will also need to have superuser, or sudo, access to both servers.

View Existing Iptables Rules

Before migrating your iptables rules, let’s see what they are set to. You can do that with this command on Server A:

sudo iptables -S
Example output:
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT

The example rules above will be used to demonstrate the firewall migration process.

Export Iptables Rules

The iptables-save command writes the current iptables rules to stdout (standard out). This gives us an easy way to export the firewall rules to file, by redirecting stdout to a file.

On the Server A, the one with the iptables rules that you want to migrate, use the iptables-save to export the current rules to a file named “iptables-export” like this:

cd ~
sudo iptables-save > iptables-export

This will create the iptables-export file, in your home directory. This file can be used on a different server to load the firewall rules into iptables.

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How To Use ProxySQL as a Load Balancer for MySQL on Ubuntu 16.04

29/09/2020 Comments off


ProxySQL is an open-source MySQL proxy server, meaning it serves as an intermediary between a MySQL server and the applications that access its databases. ProxySQL can improve performance by distributing traffic among a pool of multiple database servers and also improve availability by automatically failing over to a standby if one or more of the database servers fail.

In this guide, you will set up ProxySQL as a load balancer for multiple MySQL servers with automatic failover. As an example, this tutorial uses a multi-primary replicated cluster of three MySQL servers, but you can use a similar approach with other cluster configurations as well.


To follow this tutorial, you will need:

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Categories: Bases de données, Système Tags: ,

How To Create a High Availability Setup with Heartbeat and Floating IPs on Ubuntu 14.04

29/09/2020 Comments off

Source: Digital Ocean – Mitchell Anicas


Heartbeat is an open source program that provides cluster infrastructure capabilities—cluster membership and messaging—to client servers, which is a critical component in a high availability (HA) server infrastructure. Heartbeat is typically used in conjunction with a cluster resource manager (CRM), such as Pacemaker, to achieve a complete HA setup. However, in this tutorial, we will demonstrate how to create a 2-node HA server setup by simply using Heartbeat and a DigitalOcean Floating IP.

If you are looking to create a more robust HA setup, look into using Corosync and Pacemaker or Keepalived.


When completed, the HA setup will consist of two Ubuntu 14.04 servers in an active/passive configuration. This will be accomplished by pointing a Floating IP, which is how your users will access your services or website, to point to the primary, or active, server unless a failure is detected. In the event that the Heartbeat service detects that the primary server is unavailable, the secondary server will automatically run a script to reassign the Floating IP to itself via the DigitalOcean API. Thus, subsequent network traffic to the Floating IP will be directed to your secondary server, which will act as the active server until the primary server becomes available again (at which point, the primary server will reassign the Floating IP to itself).


Note: This tutorial only covers setting up active/passive high availability at the gateway level. That is, it includes the Floating IP, and the load balancer servers—Primary and Secondary. Furthermore, for demonstration purposes, instead of configuring reverse-proxy load balancers on each server, we will simply configure them to respond with their respective hostname and public IP address.

To achieve this goal, we will follow these steps:

  • Create 2 Droplets that will receive traffic
  • Create Floating IP and assign it to one of the Droplets
  • Create DNS A record that points to Floating IP (optional)
  • Install Heartbeat on Droplets
  • Configure Heartbeat to Run Floating IP Reassignment Service
  • Create Floating IP Reassignment Service
  • Test failover

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How To Use psad to Detect Network Intrusion Attempts on an Ubuntu VPS

28/09/2020 Comments off

Source: DigitalOcean – Justin Ellingwood


Being able to detect network activity that may indicate an intrusion attempt can help you take appropriate actions before an event occurs. Intrusion detection systems are available for this specific reason.

Intrusion detection systems are used to log suspicious connections and report when it looks like unusual activity is taking place. Some programs are used purely as a notification system, while others can actively attempt to block traffic that appear to be intent on causing harm.

The psad tool, which stands for port scan attack detection, is a piece of software that actively monitors your firewall logs to determine if a scan or attack event is in progress. It can then alert administrators, or take active steps to deter the threat.

In this guide, we will be exploring how to install and configure psad on an Ubuntu 12.04 VPS. The procedures should be fairly similar on other distributions.

Install psad

The psad intrusion detection system is available in Ubuntu’s default repositories, so it can be easily acquired through apt:

sudo apt-get update
sudo apt-get install psad

In order to configure mail delivery to alert the administrator, you will be asked to configure the postfix mail server.

In most cases, you can select “Internet Site”, and then enter the domain name associated with your server. This will be the domain portion of the name used in the “From” field in emails generated by psad.

Configure IPTables Rules

The way that psad detects activity on your server’s ports is by monitoring the logs produced by a firewall application. Ubuntu ships with the iptables firewall by default, but it is completely unconfigured and is not monitoring or blocking anything by default.

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