Middleware in the context of distributed applications is software that provides services beyond those provided by the operating system to enable the various components of a distributed system to communicate and manage data. Middleware supports and simplifies complex distributed applications. Here is a list of coding interview questions on Layering & Middleware to help you get ready for your next data structures interview in 2021.
Why is it a good idea for “lower” application layers not to be aware of “higher” ones?
The fundamental motivation is this:
You want to be able to rip an entire layer out and substitute a completely different (rewritten) one, and NOBODY SHOULD (BE ABLE TO) NOTICE THE DIFFERENCE.
The most obvious example is ripping the bottom layer out and substituting a different one. This is what you do when you develop the upper layer(s) against a simulation of the hardware, and then substitute in the real hardware.
Also layers, modules, indeed architecture itself, are means of making computer programs easier to understand by humans.
What Is Middle Tier Clustering?
Middle tier clustering is just a cluster that is used for service the middle tier in a application. This is popular since many clients may be using middle tier and a lot of heavy load may also be served by middle tier that requires it be to highly available.
Failure of middle tier can cause multiple clients and systems to fail, therefore its one of the approaches to do clustering at the middle tier of a application. In general any application that has a business logic that can be shared across multiple client can use a middle tier cluster for high availability.
Why layering your application is important? Provide some bad layering example.
Each component should contain 'layers' - a dedicated object for the web, logic and data access code. This not only draws a clean separation of concerns but also significantly eases mocking and testing the system.
Though this is a very common pattern, API developers tend to mix layers by passing the web layer objects (for example Express req, res) to business logic and data layers - this makes your application dependant on and accessible by Express only. App that mixes web objects with other layers can not be accessed by testing code, CRON jobs and other non-Express callers