有时502网关错误，没有登录error_log。如何优化nginx

Question

我有时 - 每天5到6次获得502网关错误，持续时间为30秒到40秒，似乎服务器自动启动，网站又重新启动

可悲的是 - error_log中没有这样的错误日志，显示了这个502网关错误的原因

以下是NGINX配置文件 - 是否有任何更改？

user nobody;
worker_processes 4;

error_log /var/log/nginx/error.log;
pid /var/run/nginx.pid;

events {
worker_connections  1024;
}

http {
include mime.types;
default_type application/octet-stream;

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

tcp_nopush     on;
tcp_nodelay on;

keepalive_timeout  65;
sendfile        on;
client_max_body_size 128M;
types_hash_max_size 2048;
server_names_hash_bucket_size  512;
server_names_hash_max_size 8192;
server_tokens off;

large_client_header_buffers 8 16k;

proxy_buffers 8 16k;
proxy_buffer_size 32k;
proxy_max_temp_file_size 0;

include /etc/nginx/*_maps.conf;

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=cache-pool:10m max_size=2048m;
proxy_cache_key $scheme$host$uri$is_args$args;
proxy_cache_methods GET;
proxy_cache_purge PURGE from all;
proxy_ignore_headers Cache-Control Expires Set-Cookie;
proxy_buffering on;
proxy_cache cache-pool;
proxy_cache_valid 200 3h;
add_header X-Proxy-Cache $upstream_cache_status;
include /etc/nginx/migrated/*.conf;
include /etc/nginx/vhosts/*.conf;
include /etc/nginx/server_main.conf;
}