Setup

Modified following MERN Boilerplate for this assignment:

https://github.com/keithweaver/MERN-boilerplate

Run following command in terminal to install dependencies.

npm install

For running in dev mode:

npm run start:dev

For running in prod mode:

npm start

Lint

npm run lint
npm run lintfix

Middlewares

I've used custom middleware to check payload and queries coming from front-end to make sure server only accepts which we specified for the API. For eg, try sending anything other than pageURL query in /fetch-html service.

Steps/Tech Stack

For scraping, casperjs is used, as Instagram is built using react. Make sure you have phantomjs installed and set as your env variable.
For verifying, do phantomjs -v in your terminal.
When picking stack for this app, I chose MERN as React is quite good to develop apps fast. I've used a boilerplate for setting up the baic skeleton of app but modified it a lot.
To make sure service can only be requested with a specific set number of params or payload or queries, I've build a middleware (read more in middleware section).
In case of serer down, unable to fetch message will be showed to user on submit.
I've not much focused on UI, so you'll find a very basic but functional look of page powered by bootstrap components.

Sample URLs

mukul._jain  #Private handle, will give error
jroman1964   #Will work

Improvement