I added Disqus as the tutorial.
Problem is that Disqus generates discussions duplicated with http / https.
So, discussions exist double for every posts.
How to avoid this duplication?
Discuss will generate discussions based on the address of the page it loads on. I suggest you setup your website, ie. via .htaccess to redirect all http requests to https:
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
Thank you for the reply. 
My website is on Github, and I made Github enforce to redirect http requests to https.
This is Github help link for someone like me.