connect() failed (111: Connection refused) while connecting upstream - node.js

Question

[error] 7697#7697: *100335 connect() failed (111: Connection refused) while connecting to upstream, client: XXX.XXX.XXX.XXX, server: v4.domain.com, request: "GET /socket.io/?__sails_io_sdk_version=0.13.8&__sails_io_sdk_platform=browser&__sails_io_sdk_language=javascript&EIO=3&transport=polling&t=Luvcibs HTTP/1.1", upstream: "http://127.0.0.1:1338/socket.io/?__sails_io_sdk_version=0.13.8&__sails_io_sdk_platform=browser&__sails_io_sdk_language=javascript&EIO=3&transport=polling&t=Luvcibs", host: "v4.domain.com", referrer: "http://v4.domain.com/?ct=t(Flash_Sals_Videotoolz_copy_05_12_29_2016)&mc_cid=404a630ab2&mc_eid=c44f7937fe"
[error] 7700#7700: *101735 connect() failed (111: Connection refused) while connecting to upstream, client: XX.XX.XX.XX, server: v4.domain.com, request: "GET /socket.io/?__sails_io_sdk_version=0.13.8&__sails_io_sdk_platform=browser&__sails_io_sdk_language=javascript&EIO=3&transport=polling&t=LuvciVy HTTP/1.1", upstream: "http://127.0.0.1:1338/socket.io/?__sails_io_sdk_version=0.13.8&__sails_io_sdk_platform=browser&__sails_io_sdk_language=javascript&EIO=3&transport=polling&t=LuvciVy", host: "v4.domain.com", referrer: "http://v4.domain.com/"
Recently i have configured my sails js application on Ubuntu 16.04 VPS Server which have nginx as reverse server. below is my nginx conf for site
Site runs fine but all of a sudden site break and shows 502 bad gateway.
Tried almost everything whatever i can.
Please help me to get it sorted.
server {
listen 80 default_server;
listen [::]:80 default_server;
# SSL configuration
#
listen 443 ssl default_server;
listen [::]:443 ssl default_server;
#
# Note: You should disable gzip for SSL traffic.
# See: https://bugs.debian.org/773332
#
# Read up on ssl_ciphers to ensure a secure configuration.
# See: https://bugs.debian.org/765782
#
# Self signed certs generated by the ssl-cert package
# Don't use them in a production server!
#
# include snippets/snakeoil.conf;
root /var/www/html/php;
# Add index.php to the list if you are using PHP
index index.html index.php index.htm index.nginx-debian.html;
server_name domain.com www.domain.com;
ssl_certificate /etc/letsencrypt/live/domain.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/domain.com/privkey.pem; # managed by Certbot
ssl_dhparam /etc/ssl/certs/dhparam.pem;
location / {
# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
#try_files $uri $uri/ =404;
#try_files $uri $uri/ /index.php?q=$uri&$args;
try_files $uri $uri/ /index.php?$args;
}
location ~ \.php$ {
try_files not-existing-file #php;
}
location #php {
#fastcgi_pass 127.0.0.1:9000;
fastcgi_read_timeout 300;
fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
include snippets/fastcgi-php.conf;
}
location ~* \.(css|js|png|jpg|jpeg|gif|ico)$ {
expires 1d;
}
# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
# deny all;
#}
}
upstream sails_server {
server 127.0.0.1:1338; # fail_timeout=0;
# keepalive 64;
}
server {
listen 80;
listen [::]:80;
server_name v4.domain.com;
root /root/domain/;
#Logging
error_log /root/domain/log/error.log notice;
location / {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host $host;
proxy_http_version 1.1;
proxy_set_header Connection "";
proxy_read_timeout 300;
proxy_pass http://sails_server;
proxy_redirect off;
# proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
# proxy_set_header Connection "";
# proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-NginX-Proxy true;
# proxy_cache_path /data/nginx/cache levels=1:2 keys_zone=one:10ms;
# proxy_cache one;
# proxy_cache_key sfs$request_uri$scheme;
# proxy_pass_request_headers on;
}
location /socket.io/ {
proxy_pass http://sails_server/socket.io/;
proxy_http_version 1.1;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header Port $server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Nginx-Proxy true;
proxy_pass_request_headers on;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_buffers 8 32k;
proxy_buffer_size 64k;
}
}
My PM2 config file for my sails application is below
{
"apps": [
{
"name": "dj",
"script" : "./app.js",
"watch": false,
"ignore_watch" : ["node_modules", ".tmp"],
"watch_options": {
"followSymlinks": false
},
"env" : {
"PORT": 1338,
"NODE_ENV": "production"
}
}
]
}