nginx日志的一点理解

1、access.log什么时候打印？

经过测试，观察到access.log是在后端返回响应结果之后才打印的，不过也很好理解，nginx要等后端返回才知道是否处理成功。

2、nginx什么时候出现upstream timed out？

nginx超时时间<接口响应时间，就会出现upstream timed out.

3、nginx什么时候出现no live upstreams？

测试过程日下

后端接口：

@RestController
public class BasicController {

    private static final Logger logger = LoggerFactory.getLogger(BasicController.class);
    @GetMapping("/xxx/test")
    public String hello() throws InterruptedException {
        logger.info("xxxtest");
        Thread.sleep(50000);
        return "success";
    }
}

开启了两个端口8080和8081，启动项目

nginx配置如下：

worker_processes  1;

events {
    worker_connections  1024;
}

http {
    include       mime.types;
    default_type  application/json;

    sendfile        on;
    
    keepalive_timeout  65;

    server {
        listen       80;
        server_name  localhost;
        # 指定前端项目所在的位置
       
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }


        location / {  
            # 设置超时时间  
            proxy_read_timeout 20s;  
            proxy_connect_timeout 20s;  
            proxy_send_timeout 20s;
            proxy_next_upstream error timeout;
            # 其他代理设置（可选）
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;

            proxy_pass http://backend;
        }
    }

    upstream backend {
        server 127.0.0.1:8080;
        server 127.0.0.1:8081;
    }
}

日志如下：

access.log

127.0.0.1 - - [07/Jun/2025:22:53:32 +0800] "GET /xxx/test HTTP/1.1" 502 497 "-" "PostmanRuntime/7.44.0"
127.0.0.1 - - [07/Jun/2025:22:53:50 +0800] "GET /xxx/test HTTP/1.1" 504 497 "-" "PostmanRuntime/7.44.0"

error.log

2025/06/07 22:53:30 [error] 44212#13196: *25 upstream timed out (10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond) while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET /xxx/test HTTP/1.1", upstream: "http://127.0.0.1:8081/xxx/test", host: "localhost"
2025/06/07 22:53:32 [error] 44212#13196: *27 upstream timed out (10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond) while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET /xxx/test HTTP/1.1", upstream: "http://127.0.0.1:8080/xxx/test", host: "localhost"
2025/06/07 22:53:32 [error] 44212#13196: *27 no live upstreams while connecting to upstream, client: 127.0.0.1, server: localhost, request: "GET /xxx/test HTTP/1.1", upstream: "http://backend/xxx/test", host: "localhost"
2025/06/07 22:53:50 [error] 44212#13196: *25 upstream timed out (10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond) while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET /xxx/test HTTP/1.1", upstream: "http://127.0.0.1:8080/xxx/test", host: "localhost"