在用 nginx 配置 superset 反向代理，并且使用 map 通过 cookie 分流的时候，遇到十分诡异的问题，访问主页的时候总是被重定向到 upstream 同名的域名

    upstream release {
        server 127.0.0.1:8088 weight=1 max_fails=1 fail_timeout=30s;
    }

    upstream development {
        server 127.0.0.1:8089 weight=1 max_fails=1 fail_timeout=30s;
    }

    map $COOKIE_version $env {
        default	    release;
        release	    release;
        development	development;
    }

server {
    listen       10001;
    server_name  localhost;

    location / {
        proxy_pass http://$env;
        proxy_set_header Upgrade $http_upgrade; 
        proxy_set_header Connection "upgrade"; 
        proxy_http_version 1.1; 
        proxy_connect_timeout 600; 
        proxy_send_timeout 600; 
        proxy_read_timeout 600; 
        send_timeout 600;
        proxy_set_header X-Forwarded-For $remote_addr;
    }
}

结果如下

curl -I http://127.0.0.1:10001/

HTTP/1.1 302 FOUND
Server: nginx/1.17.1
Date: Thu, 15 Aug 2019 07:54:44 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 241
Connection: keep-alive
Location: http://release/superset/welcome // 这里是重定向的 header

搞的我一度以为是不是最新版的 nginx 在 map 和 upstream 的定义上有 bug，但是想了想似乎不可能，然后从结果表现和程序员普遍的行为习惯分析来看（superset代码巨复杂，加上 python 这灵活脚本语言加成，真的不想翻它的代码），应该是代理里读取了 host 这个 header，然后 location，然后看到 nginx proxy 文档里有这句话

Allows redefining or appending fields to the request header passed to the proxied server. The value can contain text, variables, and their combinations. These directives are inherited from the previous level if and only if there are no proxy_set_header directives defined on the current level. By default, only two fields are redefined:

proxy_set_header Host  $proxy_host;
proxy_set_header Connection close;

谜题解开了。

代理配置加上这个，就可以把原本的 Host 传给 superset

proxy_set_header Host       $http_host;

curl -I http://127.0.0.1:10001/

HTTP/1.1 302 FOUND
Server: nginx/1.17.1
Date: Thu, 15 Aug 2019 08:06:47 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 241
Connection: keep-alive
Location: http://127.0.0.1:10001/superset/welcome

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