The webroot is the directory used by your webserver where you can put files that'll be accessible through your website.
I.e., if a hypothetical webroot is /var/www/htdocs/ and you'd put a file called "test" in that directory, you'd be able to access that file through http://example.com/test.
Thanks. Got it. Is there any way to find webroot for me? Because the dev ops engineer who deployed the java application has left in between and I am not aware of dev ops stuff.
Then, find the folder in your system where that page is kept. Search for key contents from the page that is shown if you have to. Try that folder in your -w option in certbot command like:
Maybe a different volunteer will walk you through your docker config but that's all I can offer for now. You need to understand your docker proxy server and the server it proxies to. You might try a docker forum. Sorry.