Nginx + Varnish Issue

l am having a lot of issue to get a wordpress site to work with varnish. l set the port to 82 in the
domain configuration and ip to 127.0.0.1 l also try my server ip no luck. also l set the varnish to default and it doesn't work l set it to wordpress and same nothing. the only error l got in 3 different servers was

Error 503 Backend fetch failed
Backend fetch failed

Guru Meditation:
XID: 3

Varnish cache server

I guess you should not change any configs manually.
And I would not use Varnish. I believe nginx+PHP-FPM 7.x the best option.

Same issue with Varnish 5.0, Magento 2.2, and nginx.

So in my case, Varnish was immediately reporting "503 backend fetch failed" with the same "no backend connection" error in varnishlog, and it turned out it was due to the probe for health_check.php returning a 404 error.

You have to try to check nginx/Apache logs. Also, try to open your website without Varnish by ports like 8080