nginx 的 upstream timed out 問題

nginx 作為負載服務，表現為網站訪問很慢，有些文件或頁面要等待到60s才會返回，我注意到60s就是超時時間，但是超時后返回狀態是正常值200，網站可以正常打開，就是會一直等待到超時才打開，而且問題出現不定時，不定文件，靜態文件也會出現這個問題。貌似很奇葩是吧，最終查看錯誤信息沒有注意到 IPv6，導致饒了不少彎。

錯誤信息：

[error] 5292#5912: *3059 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 connecting to upstream, client: 66.249.69.219, server: xxx.com, request: "GET /shop/view.jhtml HTTP/1.1", upstream: "http://[::1]:12002/shop/view.jhtml", host: "www.xxx.com"

配置如下：

    upstream zcun_pool {
        server localhost:12001 max_fails=1 fail_timeout=30s;
        server localhost:12002 max_fails=1 fail_timeout=30s;
        server localhost:12003 max_fails=1 fail_timeout=30s;
    }

發現可能是 IPv6 的問題后，改 localhost 為本地 IPv4 即可解決.....這錯誤說起來還真是低級~

    upstream zcun_pool {
        server 127.0.0.1:12001 max_fails=1 fail_timeout=30s;
        server 127.0.0.1:12002 max_fails=1 fail_timeout=30s;
        server 127.0.0.1:12003 max_fails=1 fail_timeout=30s;
    }

網站訪問回復正常。