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"