When we are developing a solution or a system, we are prone to choose a simple solution. Because simple solution is just better than complex solution. However, most of the time, we choose a simple solution inappropriately, and this causes more troubles gradually when the system is growing.
The complexity of a solution, should depend on the complexity of the problem itself, not the other way round. For example, we cannot create an operating system with a single line of programming statement. We also cannot create an operating system with just a single source file. Because an operating system is very complex (managing devices, memory, process, etc), no simple solution can fulfil the requirements.
That is why, most of the time global variables are not encouraged, because they become difficult to be managed when your source code is growing. However, if the problem is simple and global variables can solve the problem efficiently, then the approach will be acceptable.
Our human mind is limited. We cannot process too much information. Hence, if a source file contains a lot of global variables (or similar case like too many parameters in a function), we cannot process the information well. Because it is complex. And when a function is too long, with hundreds line of statements, we cannot remember what was happened in the beginning of the function. However, if we organize the variables and parameters properly, then we can process the source code much better.
As UNIX philosophy, “Do One Thing and Do It Well” (DOTADIW) (so does Microservices), this is what we ought to design our solution. We simplify the solution, not the problem, because problem cannot be changed. As a result, a very complex problem will need a lot of simple solutions or services to be built.
In reality, life form like human is complex, that is why we have multiple systems such as digestive system, respiratory system, circulatory system, etc. And each system is focusing on one task. However, the low life form organism like amoeba is very simple. We cannot expect the biological system of amoeba is workable on a human. Moreover, a large organization will need a very complex management system (not in terms of the software system), comparing to a small organization. You cannot expect the CEO have contact with thousands of employees every day in the large organization. But in a small organization, CEO can contact with every one in the team.
Therefore, if a problem is complex, or the system requirement is complex, we can only “divide and conquer” by breaking down the main problem into sub-problems, then for each sub-problem we solve it with smaller and simpler solution.
Pyramid, tree, or pipeline
When a community is growing, it will end up become a pyramid like hierarchy system. When a file folder is growing, it will end up become tree structure. If the data flow is linear, then pipeline will be the appropriate solution. Therefore, as the system is growing, your information needs to be passed from unit to unit. It is inefficient to convey the message, but it is efficient to be managed.
(But in reality, pyramid hierarchy is troublesome, because human is full of flaws and corruptions.)
Interestingly, by learning ReactJS, uses the pure function method for development helps managing the code much simpler. Because all the input of a function is immutable, or read-only. That means, you will not create a side effect to the parent component or the caller. Similar to microservices, we just need to focus on the functionality of each component.