NGINX Cookbook

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Also, it's possible to weight the servers, meaning it will preference upstream servers with a higher weight. If your servers aren't exactly the same, you can use weighting to preference your higher capacity systems so that they receive more requests. Consider this example:

upstream localapp { 
    server 127.0.0.1:8080 weight=2; 
    server 127.0.0.1:8081; 
    server 127.0.0.1:8082; 
}  

Because we set the first server with a weighted value of 2, it will receive twice as many requests as the others.