nginx responses 504/502 gateway timeout error at times - node.js

Question

I faced with a problem.
I have 6 express apps running on Node and use Nginx as a reverse proxy, all of them running without a problem for months. But recently, when I'm trying to navigate to the inner page of any of site it returned me 502 or 504 nginx error.
When I try to run apps on ngrok or locally they work correctly but on the production server, I got 504/502 error.
Nginx log says
2019/04/10 16:38:12 [error] 1362#1362: *245 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 37.9.113.120, server: my.server, request: "GET /videos/videoId HTTP/1.1", upstream: "http://127.0.0.1:3000/videos/videoId", host: "www.my.host"
I tried to increment timeouts
proxy_connect_timeout 600;
proxy_send_timeout 600;
proxy_read_timeout 600;
send_timeout 600;
But it didn't help (
Here is my server configuration.
server {
listen x.x.x.x:443 http2;
ssl on;
server_name www.myservername.com;
...(ssl conf here)
location / {
proxy_pass http://localhost:3000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}
}
I dig on StackOverflow similar topics but didn't find a solution. The most strange thing, in this case, is, after some time inner page is available but after I do loading tests and send about 100 requests on production server it stops working for about half or hour
Thanks for the help in advance.

Answer 1

You're listening on 443, using ssl, you must specify your certificates/key :
server {
listen 443 ssl;
server_name www.example.com;
ssl_certificate /var/lib/nginx/ssl/serverssl.crt;
ssl_certificate_key /var/lib/nginx/ssl/serverssl.key;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers HIGH:!aNULL:!MD5;
location / {
proxy_set_header Host example.com;
proxy_pass http://localhost:8192/;
}
}