Advanced Ha Techniques

Introduction

High Availability (HA) refers to systems that are durable and likely to operate continuously without failure for a long time. Advanced HA techniques ensure that services remain available despite hardware or software failures. In this tutorial, we will cover some advanced methods to achieve high availability in a Linux environment.

Load Balancing

Load balancing is a technique used to distribute workloads evenly across multiple servers or resources. It helps in achieving high availability by ensuring that no single server bears too much load, which could lead to its failure.

Example: Setting up Nginx Load Balancer

First, install Nginx:

sudo apt-get install nginx

Next, configure Nginx as a load balancer:

sudo nano /etc/nginx/sites-available/load_balancer

upstream backend {
    server backend1.example.com;
    server backend2.example.com;
}

server {
    listen 80;

    location / {
        proxy_pass http://backend;
    }
}

Enable the configuration and restart Nginx:

sudo ln -s /etc/nginx/sites-available/load_balancer /etc/nginx/sites-enabled/

sudo systemctl restart nginx

Failover Clustering

Failover clustering involves grouping multiple servers together to work as a single system. If the primary server fails, the secondary server takes over, ensuring zero downtime.

Example: Setting up Pacemaker and Corosync

First, install Pacemaker and Corosync:

sudo apt-get install pacemaker corosync

Configure Corosync:

sudo nano /etc/corosync/corosync.conf

totem {
    version: 2
    transport: udpu
    interface {
        ringnumber: 0
        bindnetaddr: 192.168.1.0
        mcastaddr: 226.94.1.1
        mcastport: 5405
    }
}

Start and enable Corosync and Pacemaker services:

sudo systemctl start corosync

sudo systemctl enable corosync

sudo systemctl start pacemaker

sudo systemctl enable pacemaker

Database Replication

Database replication involves copying data from one database server (master) to another (slave). This ensures data redundancy and high availability.

Example: MySQL Master-Slave Replication

On the master server, edit the MySQL configuration:

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

[mysqld]
server-id = 1
log_bin = /var/log/mysql/mysql-bin.log

Restart MySQL:

sudo systemctl restart mysql

Create a replication user:

mysql -u root -p

CREATE USER 'replica'@'%' IDENTIFIED BY 'password';
GRANT REPLICATION SLAVE ON *.* TO 'replica'@'%';
FLUSH PRIVILEGES;
SHOW MASTER STATUS;

On the slave server, edit the MySQL configuration: