nginxでURIの先頭使ってbackend serverのportを決める

nginx.conf

http {
    map $uri $backend_port {
        include port_map;
    }

    proxy_set_header X-Real-IP       $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host            $http_host;

    server {
        listen       80;
        server_name  example.com;

        if ($request_uri ~ ^/[^/]+/(.*)$) {
            set $new_uri $1;
        }
        location / {
            proxy_pass http://127.0.0.1:$backend_port/$new_uri;
        }
    }
}

port_map

default                   5000;
~^/ikachan(/.*|)$         5001;  # http://example.com/ikachan/hoge       -> http://localhost:5001/hoge
~^/cloudforecast(/.*|)$   5002;  # http://example.com/cloudforecast/fuga -> http://localhost:5002/fuga