Nginx 对上游的空响应，尽管上游是健康的

Question

所以我有一个node.js Express应用程序，后端看起来非常健康，但是nginx返回正确的状态代码，但没有响应，响应始终为空

这是我通过SSL使用3个不同子域的3x上游的配置

##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# https://www.nginx.com/resources/wiki/start/
# https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/
# https://wiki.debian.org/Nginx/DirectoryStructure
#
# In most cases, administrators will remove this file from sites-enabled/ and
# leave it as reference inside of sites-available where it will continue to be
# updated by the nginx packaging team.
#
# This file will automatically load configuration files provided by other
# applications, such as Drupal or Wordpress. These applications will be made
# available underneath a path with that package name, such as /drupal8.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##



upstream frontend {
    server web:80;
}
upstream api {
    server backend:4000;
}

upstream manage {
    server admin:5000;
}

server {

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    # root /var/www/html;

    # Add index.php to the list if you are using PHP
    # index index.html index.htm index.nginx-debian.html;
    server_name example.com test.example.com api-test.example.com www.example.com manage-test.example.com; # managed by Certbot

#    if ($subdomain = '') {
#            return 301 https://www.example.com$request_uri;
#    }
    set $upstreamed "frontend";
    if ($host = 'api-test.example.com') {
        set $upstreamed "api";
    }
    if ($host = 'api-manage.example.com') {
        set $upstreamed "manage";
    }
    location / {
        if ($request_method = 'OPTIONS') {
                add_header 'Access-Control-Allow-Origin' '*' 'always';
                add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
                #
                # Custom headers and headers various browsers *should* be OK with but aren't
                #
                add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
                #
                # Tell client that this pre-flight info is valid for 20 days
                #
                add_header 'Access-Control-Max-Age' 1728000;
                add_header 'Content-Type' 'text/plain; charset=utf-8';
                add_header 'Content-Length' 0;
                return 204;
          }
             if ($request_method = 'POST') {
                add_header 'Access-Control-Allow-Origin' '*' 'always';
                add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
                add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range' 'always';
                add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' 'always';
             }
             if ($request_method = 'GET') {
                add_header 'Access-Control-Allow-Origin' '*' 'always';
                add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, PATCH, DELETE, OPTIONS' 'always';
                add_header 'Access-Control-Allow-Headers' 'Authorization,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range' 'always';
                add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' 'always';
             }
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_redirect off;
        proxy_buffering off;
        proxy_pass http://$upstreamed;

    }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/test.example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/test.example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
server {
    if ($host = manage.test.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = api-test.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = test.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = www.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = example.com) {
        return 301 https://www.$host$request_uri;
    } # managed by Certbot


    listen 80 ;
    listen [::]:80 ;
    server_name example.com test.example.com api-test.example.com www.example.com manage-test.example.com;
    return 404; # managed by Certbot
}