响应码为200为什么还是有缓存？

Question

我在虚拟机上练习nginx负载均衡，使用默认的策略，指向两个tomcat

我用chrome浏览器访问
情况1. 在无痕窗口下可以看到轮流在两个tomcat之间切换

情况2. 在普通窗口下，却一直是同一个tomcat(快速多次刷新才偶尔有切换)
我发现响应码多为304，于是使用ctrl+f5刷新，响应码变为200(不是200 from disk cache)，但是效果还是一样

其他情况. url加上随机参数，或者使用IE8访问，可以在两个tomcat之间切换

情况2是仍然有缓存吗？还是别的因素？

---

nginx配置

upstream myserver{
  server 127.0.0.1:8080
  server 127.0.0.1:8081
}

server {
    listen       80;
    server_name  localhost;

    location / {
        proxy_pass http://myserver;
        root   html;
        index  index.html index.htm;
    }
}

普通窗口ctrl+f5的headers

#response headers
Accept-Ranges: bytes
Connection: keep-alive
Content-Length: 13
Content-Type: text/html
Date: Fri, 16 Apr 2021 16:18:19 GMT
ETag: W/"13-1618502968000"
Last-Modified: Thu, 15 Apr 2021 16:09:28 GMT
Server: nginx/1.19.10

#request headers
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Cache-Control: no-cache
Connection: keep-alive
Host: 192.168.116.128
Pragma: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36

无痕窗口的headers

#response headers
Accept-Ranges: bytes
Connection: keep-alive
Content-Length: 13
Content-Type: text/html
Date: Fri, 16 Apr 2021 16:19:53 GMT
ETag: W/"13-1618502946000"
Last-Modified: Thu, 15 Apr 2021 16:09:06 GMT
Server: nginx/1.19.10

#request headers
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Cache-Control: max-age=0
Connection: keep-alive
Host: 192.168.116.128
If-Modified-Since: Thu, 15 Apr 2021 16:09:28 GMT
If-None-Match: W/"13-1618502968000"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36

Answer 1

你请求的地址是静态资源么?

请求缓存
If-Modified-Since: Thu, 15 Apr 2021 16:09:28 GMT

响应可缓存
ETag: W/"13-1618502968000"
Last-Modified: Thu, 15 Apr 2021 16:09:28 GMT

这三行是http控制缓存的头.
不清楚是你的nginx还是tomcat加的.
如果响应If-Modified-Since, Last-Modified两个头匹配, 就会使用缓存

解决
把tomcat的缓存给禁了.