当使用index.php文件作为默认页面时，在本地机器的nginx服务器下运行多个路径，502坏网关

I try to setup a website run with different path into nginx.conf, I have 3 locations testing under the nginx conf, one is a node.js web app, one is a php forum, and the last one is phpmyadmin and it works fine. The problem is on my forum app. the index.php file shows 502 bad gateway when I test it, however it works when I use index.html. Below is configuration file, any idea about this setting?

nginx.conf

server {
listen       80;
server_name  localhost;

location / {
    proxy_pass http://nodejs;
}

location /forum {
    root  /parent/path/of/the/folder/;
    index index.php index.html;
        location ~ \.php$ {
        fastcgi_pass   127.0.0.1:9000;
        include        fastcgi.conf;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}


location /phpmyadmin3 {

  root  /usr/local/share;
  index index.php;
  # try_files $uri $uri/ /phpmyadmin/index.php$args$is_args;
        location ~ \.php$ {
        fastcgi_pass   unix:/path/to/.valet/valet.sock;
        include        fastcgi.conf;
        fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}

}

UPDATE

nginx.conf

server {
listen       80;
server_name  localhost;

location / {
    proxy_pass http://nodejs;
}

location /forum {
    root  /parent/path/of/the/folder/;
    index index.php index.html;
}


location /phpmyadmin3 {
  root  /usr/local/share;
  index index.php;
  # try_files $uri $uri/ /phpmyadmin/index.php$args$is_args;
}

location ~ \.php$ {
  fastcgi_pass   unix:/path/to/.valet/valet.sock;
  include        fastcgi.conf;
  fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
}
}