Unable to proxy pass to https backend on nginx

Sun Sep 6 14:15:28 UTC 2020

I am unable to reverse proxy to my https backend. what am i doing wrong? I
am using the same set of cert for the backend and frontend as I am running
them both on the same machine. I got my certificates from zerossl. Here is
the error I get :

curl --cacert /etc/ssl/certs/ca_bundle.crt https://www.ravi.guru

 <html>
 <head><title>502 Bad Gateway</title></head>
   <body>
   <center><h1>502 Bad Gateway</h1></center>
   <hr><center>nginx/1.16.1</center>
   </body>
 </html>
In my /var/log/nginx/error.log I get this:

2020/09/06 01:50:53 [error] 2603#0: *4 upstream SSL certificate verify
error: (2:unable to get > issuer certificate) while SSL handshaking to
upstream, client: 192.168.103.15, server: www.ravi.guru, request: "GET /
HTTP/1.1", upstream: "https://192.168.103.15:8080/", host: "www.ravi.guru"

When I connect to backend directly, all goes well:

curl --cacert /etc/ssl/certs/ca_bundle.crt https://www.ravi.guru:8080

hi

my index.html is a file with an entry "hi"

===============
Here is my config file
===============

  server {
    listen 443 http2  ssl;
    server_name www.ravi.guru;
    ssl_certificate /etc/ssl/certs/certificate.crt;
    ssl_certificate_key /etc/ssl/private/private.key;
    ssl_trusted_certificate /etc/ssl/certs/ca_bundle.crt;
    ssl_protocols           TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers             HIGH:!aNULL:!MD5;

    location / {
        proxy_pass                    https://www.ravi.guru:8080;
        proxy_ssl_certificate         /etc/ssl/certs/certificate.crt;
        proxy_ssl_certificate_key     /etc/ssl/private/private.key;
        proxy_ssl_protocols           TLSv1 TLSv1.1 TLSv1.2;
        proxy_ssl_ciphers             HIGH:!aNULL:!MD5;
        proxy_ssl_trusted_certificate /etc/ssl/certs/ca_bundle.crt;
        proxy_ssl_verify        on;
        proxy_ssl_verify_depth  2;
        proxy_ssl_session_reuse on;
    }
}
server {
listen 8080 http2 ssl;
#listen [::]:443 http2 ssl;

server_name www.ravi.guru;

ssl_certificate /etc/ssl/certs/certificate.crt;
ssl_certificate_key /etc/ssl/private/private.key;
ssl_trusted_certificate /etc/ssl/certs/ca_bundle.crt;
ssl_protocols           TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers             HIGH:!aNULL:!MD5;
root /var/www/ravi.guru/html;

index index.html index.htm index.nginx-debian.html;
}

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,289329,289329#msg-289329