How to configure load balancing in nginx

Load balancing is something we need to do for our high-traffic website. Now I will introduce to you the load balancing configuration method on the Nginx server. I hope it will be helpful to students in need. oh.

Load Balancing

First let’s briefly understand what load balancing is. If you understand it literally, it can explain that N servers share the load equally. It will not A situation where a certain server is down due to high load and a certain server is idle. Then the premise of load balancing is that it can be achieved by multiple servers, that is, more than two servers are enough.

Test environment
Since there is no server, this test directly hosts the specified domain name, and then installs three CentOS in VMware.

Test domain name: a.com

A server IP: 192.168.5.149 (main)

B server IP: 192.168.5.27

C server IP ：192.168.5.126

Deployment idea
A server is used as the main server, the domain name is directly resolved to the A server (192.168.5.149), and the A server is load balanced to the B server ( 192.168.5.27) and C server (192.168.5.126).

Domain name resolution

Since it is not a real environment, the domain name is just a.com for testing, so the resolution of a.com can only be done in hosts File settings.

Open: C:WindowsSystem32driversetchosts

Add

192.168.5.149 at the end a.com

Save and exit, then start the command mode and ping to see if Set up successfully

From the screenshot, a.com has been successfully resolved to 192.168.5.149IP

A server nginx.conf settings
Open nginx.conf , the file location is in the conf directory of the nginx installation directory.

Add the following code to the http section

upstream a.com { 
      server  192.168.5.126:80; 
      server  192.168.5.27:80; 
} 
  
server{ 
    listen 80; 
    server_name a.com; 
    location / { 
        proxy_pass         http://a.com; 
        proxy_set_header   Host             $host; 
        proxy_set_header   X-Real-IP        $remote_addr; 
        proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for; 
    } 
}

Save and restart nginx

B and C server nginx.conf settings
Open nginx.confi and add the following code to the http section

server{ 
    listen 80; 
    server_name a.com; 
    index index.html; 
    root /data0/htdocs/www; 
}

Save and restart nginx

Test
When accessing a.com, in order to distinguish which server to turn to for processing, I write an index with different content under servers B and C respectively. .html file to distinguish.

Open the browser to access a.com. Refresh and you will find that all requests are allocated by the main server (192.168.5.149) to server B (192.168.5.27) and server C (192.168.5.126). Achieved load balancing effect.

What if one of the servers goes down?
When a certain server goes down, will access be affected?

Let’s take a look at the example first. Based on the above example, assume that the machine C server 192.168.5.126 is down (since it is impossible to simulate the downtime, so I shut down the C server) and then visit it again.

Access results:

We found that although the C server (192.168.5.126) was down, it did not affect website access. In this way, you won't have to worry about dragging down the entire site because a certain machine is down in load balancing mode.

What if b.com also needs to set up load balancing?
It's very simple, the same as a.com settings. As follows:

Assume that the main server IP of b.com is 192.168.5.149, and the load is balanced to 192.168.5.150 and 192.168.5.151 machines.

Now resolve the domain name b.com to 192.168.5.149 on IP.

Add the following code to nginx.conf of the main server (192.168.5.149):

upstream b.com { 
      server  192.168.5.150:80; 
      server  192.168.5.151:80; 
} 
  
server{ 
    listen 80; 
    server_name b.com; 
    location / { 
        proxy_pass         http://b.com; 
        proxy_set_header   Host             $host; 
        proxy_set_header   X-Real-IP        $remote_addr; 
        proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for; 
    } 
}

Save and restart nginx

at 192.168.5.150 and 192.168 .Set nginx on the 5.151 machine, open nginx.conf and add the following code at the end:

server{ 
    listen 80; 
    server_name b.com; 
    index index.html; 
    root /data0/htdocs/www; 
}

Save and restart nginx

After completing the next steps, you can implement the load balancing configuration of b.com.

Can’t the main server provide services?
In the above examples, we have applied the load balancing of the main server to other servers, so can the main server itself be added to the server list, so that it will not be wasted using a server purely as a forwarding function, and Yes, they are also involved in providing services.

Such as the above case of three servers:

A server IP: 192.168.5.149 (main)

B server IP: 192.168.5.27

C server IP: 192.168.5.126

We resolve the domain name to server A, and then forward it to server B and server C from server A. Then server A only performs a forwarding function. Now we let server A also provide site services.

Let’s analyze it first. If you add the main server to upstream, the following two situations may occur:

1. The main server is forwarded to other IPs, and other IP servers are normal. Processing;

2. The main server forwards it to its own IP, and then goes to the main server to allocate IP. If it is always allocated to the local machine, it will cause an infinite loop.

How to solve this problem? Because port 80 has been used to monitor load balancing processing, port 80 can no longer be used on this server to process access requests for a.com, and a new one must be used. So we added the following code to the main server's nginx.conf:

server{ 
    listen 8080; 
    server_name a.com; 
    index index.html; 
    root /data0/htdocs/www; 
}

Restart nginx and enter a.com:8080 in the browser to see if it can be accessed. The result can be accessed normally

Since it can be accessed normally, we can add the main server to upstream, but the port needs to be changed, as shown in the following code:

upstream a.com { 
      server  192.168.5.126:80; 
      server  192.168.5.27:80; 
      server  127.0.0.1:8080; 
}

由于这里可以添加主服务器IP192.168.5.149或者127.0.0.1均可以，都表示访问自己。

重启Nginx，然后再来访问a.com看看会不会分配到主服务器上。

主服务器也能正常加入服务了。

最后
一、负载均衡不是nginx独有，著名鼎鼎的apache也有，但性能可能不如nginx。

二、多台服务器提供服务，但域名只解析到主服务器，而真正的服务器IP不会被ping下即可获得，增加一定安全性。

三、upstream里的IP不一定是内网，外网IP也可以。不过经典的案例是，局域网中某台IP暴露在外网下，域名直接解析到此IP。然后又这台主服务器转发到内网服务器IP中。

四、某台服务器宕机、不会影响网站正常运行，Nginx不会把请求转发到已宕机的IP上。

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