如何配置nginx解决502网关错误？

Question

我在后端有一个nodeJs API，在前端有UI。我在UI和API之间建立了nginx反向代理，并通过SSL建立了连接。

API正在使用8080端口，nginx配置指向API的8080端口。但是访问UI时出现502网关错误。

这是我的Nginx配置文件。

#
# 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.
##

# Default server configuration
#
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 adviceto.me www.adviceto.me;

        location / {
                proxy_pass http://127.0.0.1:8080;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
        }

        # pass PHP scripts to FastCGI server
        #
        #location ~ \.php$ {
        #       include snippets/fastcgi-php.conf;
        #
        #       # With php-fpm (or other unix sockets):
        #       fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
        #       # With php-cgi (or other tcp sockets):
        #       fastcgi_pass 127.0.0.1:9000;
        #}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #       deny all;
        #}

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/adviceto.me/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/adviceto.me/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
}

# Virtual Host configuration for example.com
#
# You can move that to a different file under sites-available/ and symlink that
# to sites-enabled/ to enable it.
#
#server {
#       listen 80;
#       listen [::]:80;
#
#       server_name example.com;
#
#       root /var/www/example.com;
#       index index.html;
#
#       location / {
#               try_files $uri $uri/ =404;
#       }
#}

server {
    if ($host = beta.adviceto.me) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


        listen 80 default_server;
        listen [::]:80 default_server;

        server_name beta.adviceto.me;
    return 404; # managed by Certbot


}

#server {
#    if ($host = beta.adviceto.me) {
#        return 301 https://$host$request_uri;
#    } # managed by Certbot
#    server_name adviceto.me; # managed by Certbot
#    return 404; # managed by Certbot




#    listen [::]:443 ssl; # managed by Certbot
#    listen 443 ssl; # managed by Certbot
#    ssl_certificate /etc/letsencrypt/live/beta.adviceto.me/fullchain.pem; # managed by Certbot
#    ssl_certificate_key /etc/letsencrypt/live/beta.adviceto.me/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 ($host = adviceto.me) {
        return 301 https://$host$request_uri;
    } # managed by Certbot




        listen 80 ;
        listen [::]:80 ;
    server_name adviceto.me;
    return 404; # managed by Certbot


}

这是nginx错误：

connect() failed (111: Connection refused) while connecting to upstream, client: 88.230.230.75, server: adviceto.me

我找不到任何解决方案。您能帮我吗？