使用docker和Nginx在.net核心API上获取HTTP 502错误网关

我有两个docker容器，分别运行在我的机器（Linux）上的两个不同的net core API项目

3333:80

和

6666:8088

。我已经在Nginx服务器上部署了它们的前端部分，每个前端在sitesavailable文件夹中都有自己的配置。 问题是，我的第一个容器（API）工作正常，从前端应用程序和邮递员处获得响应，但第二个容器不工作，抛出此错误

HTTP 502坏网关

和错误消息：

recv() failed (104: Connection reset by peer) while reading response header from upstream

这里怎么了？请帮我解决这个问题。以下是我的配置文件： nginx.conf：

user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

events {
    worker_connections 768;
    # multi_accept on;
}

http {

    ##
    # Basic Settings
    ##
    client_max_body_size 50M;   
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    # server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

site1.conf

server {
    listen 80 default_server;

    server_name _;

    root /var/www/app.admin-crm.com;
    index index.html;

    location /api/ {
        proxy_pass      http://127.0.0.1:3333/api/;
        proxy_redirect  off;
        proxy_set_header        X-Real-IP $remote_addr;
        proxy_set_header        X-Forwarded_For $proxy_add_x_forwarded_for;
        proxy_set_header        X-Forwarded_Host $server_name;
        add_header      Access-Control_Allow-Credentials true;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        client_max_body_size    50M;
    }

    location / {
        try_files $uri $uri/ /index.html;
    }
 }

site2.conf：

server {
    listen 8088 default_server;

    server_name _;

    root /var/www/stilaar-web;
    index index.html;

    location /api/ {
        proxy_pass      http://127.0.0.1:6666/api/;
        proxy_redirect  off;
        proxy_set_header        X-Real-IP $remote_addr;
        proxy_set_header        X-Forwarded_For $proxy_add_x_forwarded_for;
        proxy_set_header        X-Forwarded_Host $server_name;
        add_header      Access-Control_Allow-Credentials true;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        client_max_body_size    50M;
    }

    location / {
        try_files $uri $uri/ /index.html;
    }

}