Setting up hashnode's blog
No surprise. It took me around 30 mins to figure out how to create a sub-domain for my existing portfolio page. I have my portfolio website domain hosted on NameCheap. If you are using the same hosting provider, then these are the steps to create a sub-domain for your blog page.
My portfolio page: https://jayaganeshkumar.me/
My blog page: blog.jayaganeshkumar.me.
Step-1: Login to your Namecheap account where you hosted your portfolio page.
Step-2: Go to "Domain list" >> Click on "manage" with respect to your domain.
Step-3: Go to the "Advanced DNS" and click on "Add new record" in the "Host Records" section.
Step-4: Now select "A record" in "type" and write "blog" in "host" and write "192.241.200.144" (IP address of hashnode.dev) in "value" section.
Step-5: Save changes and wait until they integrate.
It took me around 10 minutes to integrate the sub-domain. It can even take more time, but the process will be completed within 24 hours. After 24 hours, you can check your blog site by typing "blog." in your browser.