Hi there,

I've posted this on Stack Overflow and hoping someone can help me here.

I am new to nginx and am trying to configure a reverse proxy to a Shiny Server (Open) that I have successfully implemented on an AWS Lightsail Instance. I am desperate at this point and would appreciate any advice. Here are the pertinent configuration arrangements.

Note that I have a purchased a custom domain from GoDaddy. Assume this is named mydomain.com.au. However, I have changed the name servers to point to Netlify as I deployed my website through the blogdown R package in Netlify.
Lightsail Instance Details

This has a Shiny Server installed and a static IP address assigned. Assume 123.45.67.89 from this point onwards. The firewall details are provided below:

Lightsail instance firewall details

I can successfully access the Shiny Server via http://123.45.67.89:3838 and associated Shiny apps I've deployed. I have a DNS Zone record added in order to link mydomain.com.au to my Shiny Server on the Lightsail instance - see details below:

Record Type: A
Subdomain: shiny.mydomain.com.au
Resolves to: 123.45.67.89 (i.e. static IP address)

Netlify details

I have a DNS record added in Netlify for mydomain.com.au which points to the Lightsail instance static IP address. Below are the details (I'm not sure whether I need a DNS record in Netlify and Lightsail though). Note this this is SSL/TLS certificate enabled and cannot be disabled (it will automatically revert to "https://" even when "http://" is specified).

Name: shiny.mydomain.com.au
TTL: 3600 seconds
Type: A
Value: 123.45.67.89

nginx details

Below are the relevant details of the /etc/nginx/sites-enabled/default file which I modified based on the instructions from this post. The $http_upgrade and $connection_upgrade is stored in the /etc/nginx/nginx.conf file. There is no SSL/TLS certificate from certbot added and I'm not sure whether this is an issue.

server {
listen [::]:80 default_server;

root /var/www/html;

# Add index.php to the list if you are using PHP
index index.html index.htm index.nginx-debian.html;

server_name shiny.mydomain.com.au;

# Reverse proxy to port 3838
location / {
proxy_pass http://localhost:3838/;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;
proxy_read_timeout 20d;
proxy_buffering off;

# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
# try_files $uri $uri/ =404;
}

The nginx configuration test appears to be successful:

sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

The following firewall profiles (from sudo ufw status) are set up - Nginx HTTP, OpenSSH, 3838 and 80. nginx is active and running too with no issues according to sudo service nginx status.
What works?

http://123.45.67.89:3838/ successfully opens the Shiny Server index page.
https://shiny.mydomain.com.au:3838/ successfully opens the Shiny Server index page.

Other information?

Visiting https://shiny.mydomain.com.au:3838 will automatically attempt https://123.45.67.89:443 which ultimately fails and times out. The redirection to 123.45.67.89 appears to work but it does not forward to the 3838 port. Firefox Network monitoring indicates that the Server is nginx.

What might be happening?

At this point (and I am very new to web administration), I think this might be an issue with Netlify forcing HTTPS which cannot be redirect to the Shiny Server port (HTTP?). However, visiting https://shiny.mydomain.com.au:3838 successfully redirects to the Shiny Server index page. I just can't understand why nginx isn't successfully forwarding to the 3838 port without specifying it in the URL based on the default configuration file.
What is the problem?

Loading shiny.mydomain.com.au does not successfully load the Shiny Server index page. It will eventually time out and no page is loaded ("The connection has timed out"). Checking the network monitoring information in Firefox indicates that tries to access 123.45.67.89 but not 123.45.67.89:3838 (i.e. the Shiny Server). It doesn't appear that it is redirecting at all according to the /etc/nginx/sites-enabled/default file.

I have tried changing localhost to 127.0.0.1 to no avail. I have tried following Dean Attali's post and another recent post on setting up Shiny Server too but still no success.

Can someone please help me out on how to get nginx as a reverse proxy to work?

I'm really running out of ideas here. Thanks.