当上游服务器重新启动且未恢复正常时，NGINX 显示“错误网关”

每次当我重新启动上游服务器时，我的 NGINX 显示“坏网关”，这没关系，但后来，当上游服务器重新启动 nginx 时，nginx 不会自动恢复，我需要手动重新启动它（nginx）。

是否有一个选项可以让 nginx 每隔几秒检查一次上游是否恢复正常？

    upstream core {

    server core:3001;
}

server {
    server_name core.mydomain.com corestg.mydomain.com www.core.mydomain.com;

    #listen 80;
    #listen [::]:80;

    gzip on;
    gzip_static on;    
    gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript application/javascript;
    gzip_proxied  any;
    #gzip_vary on;
    gzip_comp_level 6;
    gzip_buffers 16 8k;
    gzip_http_version 1.1;    
     listen 443 ssl http2;
     listen [::]:443 ssl http2;

    resolver 8.8.8.8 8.8.4.4 valid=300s;
    resolver_timeout 5s;

    server_tokens off;
    ssl_certificate /etc/ssl/domain.crt;
    ssl_certificate_key /etc/ssl/domain.rsa; 

    error_log  /var/log/nginx/error.log;
    access_log /var/log/nginx/access.log;

    location / {
        proxy_ssl_session_reuse off;
        proxy_pass http://core;
        proxy_buffers 8 24k;
        proxy_buffer_size 2k;
        proxy_http_version 1.1;
        proxy_ignore_headers X-Accel-Expires Expires Cache-Control;
        proxy_ignore_headers Set-Cookie;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header X-NginX-Proxy true;
#       proxy_set_header Host $http_host;
        proxy_set_header Host $host;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_cache_bypass $http_upgrade;
        proxy_redirect off;
    }
}

看来 NGINX 默认情况下不进行自动恢复。 更改配置部分：

upstream core {
    server core:3001;
}

to:

{
    server core:3001  max_fails=1 fail_timeout=1s;
    server core:3001  max_fails=1 fail_timeout=1s;
}

成功了。重复不是错误。 Nginx 尝试解析第一行，失败时它将尝试第二行（循环）。