How to deploy a high-availability architecture in Linux

With the advent of the big data era, more and more companies and organizations are beginning to use Linux operating systems as their server platforms. In order to ensure the availability and stability of applications, high-availability architecture has become an indispensable part of Linux servers. This article will introduce how to deploy a high-availability architecture in Linux.

What is a high availability architecture?

High Availability (HA) refers to a system architecture that can continue to provide services when the system fails. HA can be implemented through a variety of technologies, such as load balancing, redundant backup, failover, etc. For enterprise-level applications, maintaining high availability is critical because it ensures that the application can continue to function normally in the event of unexpected circumstances.

Steps to deploy a high-availability architecture in Linux

1. Network planning

First, you need to plan the network. To ensure high availability, each node in the cluster should be assigned an independent IP address and combined into a virtual IP address. In addition, network storage needs to be configured for the cluster to share data between nodes.

2. Install software

Before installing the software, install the necessary software packages on each node, such as heartbeat, corosync and pcs packages. It can be installed on CentOS using the following command:

sudo yum install corosync pcs pacemaker resource-agents

3. Configure Corosync and Heartbeat

Next, Corosync and Heartbeat need to be configured to enable communication between the two nodes . This is one of the key steps to ensure high availability. Set the node's IP address, channel name, and channel port in the configuration file. During this configuration process, ensure that the following information is configured:

• bindnetaddr: Specifies the network interface address used for communication between nodes.
• mcastaddr: used to specify the multicast address.
• mcastport: used to specify the port number of the multicast channel.

totem {
        version: 2
        secauth: off
        interface {
                ringnumber: 0
                bindnetaddr: 192.168.50.0
                mcastaddr: 226.94.1.1
                mcastport: 5405
        }
        transport: udpu
}

logging {
        to_logfile: yes
        logfile: /var/log/corosync/corosync.log
        to_syslog: yes
}

In the heartbeat configuration file, you need to set the IP address and virtual IP address of the node. Make sure the application serving the virtual IP address is installed.

#设定hacluster集群名称
cluster hacluster
#设定故障探测时间间隔 必须<ping的-send值
keepalive 2
#每次探测(waitting)会加入2秒
deadtime 10
#装备ping用的参数,每次等待10秒
warntime 10
initdead 20
udpport 694
#主服务节点IP，可多行填写
node node1.example.com
node node2.example.com
#关联的主节点为node1，次节点为node2
crm respawn
#virtual_ip是虚拟IP
#Ethernet Bridge 和IP假设设为192.168.0.1/24
primitive virtual_ip ocf:heartbeat:IPaddr2 
        params ip="192.168.0.5" cidr_netmask="24" 
        op monitor interval="10s"
#IP暂停服务后强制迁移
location virtual_ip-primary virtual_ip 
        rule $id="virtual_ip-rule" inf: virtual_ip

4. Configuring the cluster management tool

Install the pcs tool, which is a command line tool used to configure the Pacemaker cluster management software. It can be installed using the following command:

sudo yum install pcs
sudo systemctl enable pcsd.service && sudo systemctl start pcsd.service

Configure the firewall to ensure that the firewall on any node allows communication. On CentOS7, you can use the following command:

sudo firewall-cmd --add-service=high-availability --permanent
sudo firewall-cmd --reload

On each node, create the hacluster user and add it to the pcsd group for future management of the Pacemaker cluster:

sudo useradd hacluster
sudo passwd hacluster
sudo usermod -aG pcsd hacluster

To enable pcsd service, please use the following command:

sudo systemctl enable pcsd
sudo systemctl start pcsd

Use the following command to configure authkey on Pacemaker and copy the authkey to all other nodes using the same options:

sudo pcs cluster auth <node1.example.com> <node2.example.com> -u hacluster -p <password> --force

5. Configure Load Balancing

Install and configure HAproxy, which is a high-availability load balancing tool for TCP and HTTP applications. You can use the following command to install it on CentOS:

sudo yum -y install haproxy
sudo systemctl enable haproxy

In the haproxy configuration file, you need to set the load balancing algorithm, the IP address and port number of the backend server.

global
    log         127.0.0.1 local2
    chroot      /var/lib/haproxy
    pidfile     /var/run/haproxy.pid
    maxconn     4000
    user        haproxy
    group       haproxy
    daemon      # Enables HAProxy in daemon mode

defaults
    log         global
    mode        http
    option      httplog
    option      dontlognull
    retries     3
    option      redispatch
    maxconn     2000
    contimeout  5000
    clitimeout  50000
    srvtimeout  50000

frontend web
    bind *:80
    mode http
    default_backend web-backend

backend web-backend
    mode http
    balance roundrobin
    option httpchk HEAD / HTTP/1.1
Host:localhost
    server node1 10.0.0.2:80 check
    server node2 10.0.0.3:80 check

6. Test high availability architecture

Finally, test high availability. Disconnect one of the nodes and ensure that the virtual IP is automatically transferred to the other node. Confirm that applications on other nodes are running normally under the virtual IP to ensure high availability.

Conclusion

Deploying a high-availability architecture in Linux can ensure the stability and availability of enterprise applications in the face of unexpected failures. Using the HA architecture based on Corosync and Heartbeat, applications can be distributed to different server nodes through virtual IP addresses and load balancing algorithms to ensure their high availability and performance.

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