Detailed description of health check and automatic failure recovery of Nginx server

Nginx server health check and automatic failure recovery detailed description

Introduction:
In today's Internet applications, high concurrency and high availability are very important. In order to ensure the stability of the system, we need to monitor and check the health of the server and automatically perform fault recovery. This article will explain in detail how to use Nginx server for health check and automatic failure recovery, and give relevant code examples.

1. Nginx health check principle
   In the Nginx configuration file, we can define a group of backend servers through the upstream module, and Nginx will allocate requests to different servers according to a certain algorithm. During this process, Nginx can dynamically adjust the distribution of requests by checking the health of the backend server. There are two commonly used health check methods:

1.1 Active health check:
Nginx will periodically send requests to the backend server, and then determine the health of the server based on the returned status code. situation. If the returned status code indicates that the server is normal, Nginx will add the server to the available server list; if the returned status code indicates that the server is abnormal, Nginx will remove the server from the available server list.

1.2 Passive health check:
When Nginx sends a request to the backend server and the connection times out or the request fails, Nginx will determine that the server is an unavailable server and remove it from the list of available servers. When a new request arrives, Nginx will try to connect to other available servers.

2. Nginx health check configuration example
   In the Nginx configuration file, we can enable the health check function through the health_check parameter in the upstream module and configure related health check items. The following is an example configuration:

http {

upstream backend {
    server backend1.example.com;
    server backend2.example.com;
    server backend3.example.com;
    
    # 开启健康检查功能
    health_check;
    
    # 配置健康检查项
    health_check_timeout 3s;
    health_check_interval 10s;
    health_check_http_2xx;
    health_check_http_3xx;
}

server {
    listen 80;
    
    location / {
        proxy_pass http://backend;
    }
}

}

In the above configuration, we define an upstream group named backend and configure There are three backend servers. By setting the health_check parameter to on, the health check function is enabled. The specific configuration of the health check items is as follows:

• health_check_timeout: Set the health check timeout.
• health_check_interval: Set the health check interval.
• health_check_http_2xx: When the returned status code is 2xx (such as 200), it means that the server is normal.
• health_check_http_3xx: When the returned status code is 3xx (such as 301, 302), it means that the server is normal.

3. Nginx automatic failure recovery configuration example
   In addition to health check, Nginx also provides automatic failure recovery function. When a backend server is judged to be unavailable, Nginx will automatically remove it from the list of available servers and perform a health check again after a period of time. If the backend server passes the health check, Nginx will add it to the list of available servers again to achieve automatic failure recovery. The following is an example configuration:

http {

upstream backend {
    server backend1.example.com;
    server backend2.example.com;
    server backend3.example.com;
    
    # 开启健康检查和自动故障恢复功能
    health_check;
    max_fails 3;
    fail_timeout 30s;
    
    # 配置健康检查项
    health_check_timeout 3s;
    health_check_interval 10s;
    health_check_http_2xx;
    health_check_http_3xx;
}

server {
    listen 80;
    
    location / {
        proxy_pass http://backend;
    }
}

}

In the above configuration, we added two parameters, max_fails and fail_timeout, for configuring automatic Fault recovery function.

• max_fails: Set the maximum number of failures within a certain period of time (specified by the fail_timeout parameter). By default, it is 1 time.
• fail_timeout: Set the timeout for failure recovery.

When the number of failures of a backend server reaches the value configured by max_fails, Nginx will remove the server from the list of available servers and perform a health check again after the timeout configured by fail_timeout. . If the server passes the health check, Nginx will add it to the list of available servers again.

Conclusion:
The health check and automatic fault recovery functions of the Nginx server can effectively improve the stability and availability of the system. Through the above configuration examples, we can easily configure Nginx to implement health check and automatic failure recovery functions. I hope this article will help you understand and use the health check and automatic failure recovery functions of the Nginx server.

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