I would like to set the stage for this article with an opening sentence.
Microservice architecture is not a swiss army knife
Understanding this phrase will make us ready to dive into the world of Microservices and discover its advantages as well as drawbacks. This phrase will help us perceive if Microservices Architecture is the right choice for our next project.
Microservices architecture is a way of architecting software applications involving multiple self-contained services. Each service provides specific business functionality and follows its own development and deployment cycle. This is synonymous to the Lego bricks which can be connected to create different objects. Similarly, multiple microservices can be mashed up to create an application that provides a more concrete value to the end users.
Microservices thus offer a reusable infrastructure which can be used in different contexts, e.g., a Messaging app encapsulates messaging service so it can be used with a Banking App, eCommerce App, Ticketing App, etc. It encapsulates the messaging domain so that other applications don’t have to worry about re-inventing the wheel for the messaging system.
Microservices are genuinely independent of each other; they are loosely coupled without any binary dependency between them. They only use each other’s services defined by messaging protocols or external API contracts.
Each of these services can evolve independently, one thing to keep in mind is that these services need to be evolved in a backward compatible way. If care is not taken, it will create a situation where other microservices need to be deployed in lock-step.
Microservices are small, easily manageable applications; therefore it is easy for engineers to get up to speed and be able to contribute without understanding the overall applications architecture. If the whole system is reasonably complex, this also helps with creating agile teams that focus on particular microservices.
Microservices are easy to test, writing the end to end acceptance or integration tests do not require a pile of data to be set up. Each microservice focuses on its domain; therefore data setup for testing is relatively straight forward.
Each properly crafted microservice has its database, which is chosen based on the requirements for that particular domain. Significant schema changes in one microservice do not affect other microservices. This helps tremendously with fewer down times.
If one microservice is hit with the outage, it does not have a significant impact on the usability of the entire system, as other microservices continue to provide their services. This, however, may not be true in case of a microservice which is central to the system such as Authentication App.
Each microservices can use the technology stack, including development language, frameworks, databases, etc suitable for solving problems for that particular domain.
In terms of security, even though microservices have a larger surface area that needs to be secured, but even in case of a breach, only the data managed by that microservice is at risk. Other microservices are not affected as they either have their separate databases or if they share the same database, they will have a different schema and credentials.
Best of all each service can be deployed on the most optimized hardware for that service. If one service requires more memory whereas others require more CPU, then they can each be deployed on the hardware which fulfills those requirements.
Microservices have a fairly small footprint; therefore it takes less time to build and launch, this helps engineers tremendously, giving them the ability to make changes and get much quicker feedback.
Deployment of microservices is effortless, provided they are enhanced in a backward compatible fashion. So utmost attention should be paid not to make changes which will break the contract with external clients, as it will require external clients to be upgraded in lockstep.
Microservices applications are easy to scale, it is easy to identify highly utilized services and focus on scaling just those services rather than scaling the whole infrastructure.
So far we were focused entirely on the good parts of microservices. However, as I mentioned early, it’s not a one size fits all architecture. It is well suited for some applications but not for others.
One issue is with designing the microservices, as it is difficult to come up with a microservice with well-defined boundaries. If the microservices are not crafted with the correct boundaries, they can drive the application towards a big, and messy dependency web. Where each microservice depends on various other services which in turn depend on more services and so on, microservices need to be modularized based on the business domain or functional boundaries which have minimal dependency on each other.
Transaction management across multiple services is the most challenging part of the microservice architecture. Imagine on an e-commerce website, a customer places an order by calling order management microservice, and payment processing is handled by some other microservice. What will happen if the order is placed successfully, but the payment processing fails. There needs to be appropriate infrastructure in place to reverse the order if the payment fails, which of course would be more challenging to handle compared to transactions handled at the database level.
If we look at the overall application comprising of multiple microservices, there are more moving parts, so a lot more places where things can go wrong.
Debugging an issue in microservices based platforms is also exceptionally difficult. The request has to travel through multiple microservices, so pinpointing the exact location where an error or exception occurred is cumbersome.
Hopefully, the advantages and disadvantages outlined in this article will help the reader decide which architecture to choose when designing an application.