Failover and recovery mechanism in Nginx load balancing solution

Introduction:
For high-load websites, the use of load balancing is to ensure high availability and One of the important means to improve performance. As a powerful open source web server, Nginx's load balancing function has been widely used. In load balancing, how to implement failover and recovery mechanisms is an important issue that needs to be considered. This article will introduce the failover and recovery mechanism in Nginx load balancing and give specific code examples.

1. Failover mechanism
Failover refers to the ability of the system to seamlessly transfer the load to other normal nodes when one or multiple nodes fail. Nginx provides a variety of failover mechanism configuration options. Here are some commonly used methods.

1. Health check-based failover
   Nginx’s upstream module provides a failover mechanism based on active health checks. By regularly sending health check requests to the backend server, the availability of the node can be judged and load balancing can be performed based on the check results. When a node fails, Nginx will automatically forward requests to other normal nodes to achieve failover.

The following is an example of a load balancing configuration based on health check:

upstream backend {
    server backend1.example.com:80;
    server backend2.example.com:80;
    check interval=3000 rise=2 fall=3 timeout=1000;
}

server {
    listen 80;
    server_name example.com;

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

In the above configuration, a health check request will be sent to the backend server every 3 seconds. When there are two consecutive normal responses, the node is considered to be back to normal; when there are three consecutive abnormal responses, the node is considered to be faulty. Nginx will perform load balancing based on node availability and automatically switch to normal nodes.

2. Failover based on active detection
   The stream module of Nginx provides a failover mechanism based on active detection. By periodically sending probe requests to the backend server, the availability of nodes can be detected and load balancing can be performed based on the probe results. When a node fails, Nginx will automatically forward the request to other normal nodes to achieve failover.

The following is an example of a load balancing configuration based on active detection:

stream {
    upstream backend {
        server backend1.example.com:80;
        server backend2.example.com:80;
        check interval=3000 rise=2 fall=3 timeout=1000;
    }

    server {
        listen 80;
        proxy_pass backend;
    }
}

In the above configuration, a detection request will be sent to the backend server every 3 seconds. When there are two consecutive normal responses, the node is considered to be back to normal; when there are three consecutive abnormal responses, the node is considered to be faulty. Nginx will perform load balancing based on node availability and automatically switch to normal nodes.

2. Failure recovery mechanism
Failure recovery refers to the ability of the system to automatically redistribute the load to the node after a node failure is repaired. Nginx provides a variety of configuration options for failure recovery mechanisms. Here are some commonly used methods.

1. Failure recovery based on health check
   Nginx’s upstream module also provides a failure recovery mechanism based on active health check. After the node's availability is restored, Nginx will automatically redistribute requests to the node.

The following is an example of a health check-based failure recovery configuration:

upstream backend {
    server backend1.example.com:80;
    server backend2.example.com:80;
    check interval=3000 rise=2 fall=3 timeout=1000;
}

server {
    listen 80;
    server_name example.com;

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

In the above configuration, when the availability of a node is restored, Nginx will automatically redistribute requests to the node.

2. Weight-based failure recovery
   Nginx’s upstream module also provides a weight-based failure recovery mechanism. By setting different weight values ??for nodes, you can control the load distribution ratio. When the availability of a node is restored, the weight value of the node can be adjusted to gradually return it to normal load status.

The following is an example of a weight-based fault recovery configuration:

upstream backend {
    server backend1.example.com:80 weight=5;
    server backend2.example.com:80 weight=1;
}

server {
    listen 80;
    server_name example.com;

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

In the above configuration, the weight of the backend server backend1 is 5, and the weight of the backend server backend2 is 1. When the availability of backend1 is restored, its weight value can be adjusted so that it gradually returns to 5 to achieve failure recovery.

Conclusion:
This article introduces the failover and recovery mechanism in the Nginx load balancing solution and gives specific code examples. By properly configuring failover and recovery mechanisms, system availability and performance can be improved. In actual applications, the appropriate configuration method can be selected according to specific needs and scenarios to achieve the optimal load balancing effect.

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