The problem with a question like this, and what Graeme_Grant brings up is that the company wants you to answer these questions, not get strangers on the internet to answer them for you. If you were to use google and research the fundamentals of your issues you bring up yourself that's one thing as that would demonstrate your ability to figure things out and solve problems.
Another comment here, you say
Quote: I tried to found the solution on google but not find any till.
But this isn't a question or answer you can google. if it were, do you think they would hire you? They would just use google to quickly solve their problems. They are looking to hire you
to solve their problems.
But I can guarantee that if you were to get this position, in the near future both you and the company are going to be frustrated because they are going to think you can't perform due to your inability to do the work asked of you, and you are going to get frustrated from not being able to keep up.
In the spirit of helping you help yourself, my suggestion would be to break down your many questions into smaller problems. Don't look at this as a daunting task of 5 problems that you have to solve, start with the first one and only that one.
Quote:Stock Service will run 24/7 hours (i.e need load balance kind of thing).
So you need your servers available 24/7. What all do you think this entails? One server going to cut it? What about idle time issues? What do you think needs to be accomplished here? There is no right or wrong answer as this is an interview question for you. The idea being that the company wants to see what you know...not what I or anyone else here knows. Start by explaining what infrastructure you think you need to server an app 24/7 for different clients (your #2)
Now work your way down the list of bullet points you've laid out, look at each item individually and what it entails. Get all your thoughts for each bullet point together then start to massage those thoughts to fit the big picture of serving an application 24/7 to many different clients that needs to support large volume of transactions.