How to fix 502 Bad Gateway Error in nginx php

When huge request hits on nginx server it returns 502 bad gateway error. I have tried multiple answer from stackoverflow including this How to fix 502 Bad Gateway Error in production(Nginx)? But nothing works for me. Someone help for me

worker_processes 1; daemon off; user root; events { worker_connections 1024; } http { include /etc/nginx/mime.types; default_type application/octet-stream; sendfile on; keepalive_timeout 330; client_max_body_size 512M; server_tokens off; gzip on; gzip_types application/json; access_log /dev/stdout; error_log /dev/stdout; # Adding proxy timeout proxy_read_timeout 330; proxy_connect_timeout 330; proxy_send_timeout 330; server { listen 80; server_name _; root /var/www/html/public; index index.php index.html index.htm; underscores_in_headers on; access_log /dev/stdout; error_log /dev/stdout; location ~ \.php$ { try_files $uri =404; fastcgi_split_path_info ^(.+\.php)(/.+)$; fastcgi_pass 127.0.0.1:9000; fastcgi_index index.php; fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name; fastcgi_param SCRIPT_NAME $fastcgi_script_name; include /etc/nginx/fastcgi_params; fastcgi_send_timeout 330; fastcgi_read_timeout 330; fastcgi_busy_buffers_size 16k; fastcgi_buffer_size 16k; fastcgi_buffers 4 16k; } location / { # try to serve file directly, fallback to index.php try_files $uri /index.php$is_args$args; } } }