Yes and No.
Yes when we are facing problems that it solves and No when we blindly follow that “trend”.
Once my boss read somewhere about how amazing the Microservices is and instantly he asked the development team to “Let do Microservices”. He’s purely a business man but always want to apply the newest technology. How lucky am I, but also a challenge when to switch a system design to another. Actually it sounds cool to us so it is a quickly agreement between boss and developers. So let do Microservices.
What is Microservices ?
Microservices, clearly said, is a system design approach, I personally don’t count it as a technology. Microservices system itself will be composed from multiple technologies. Each piece of technology solves a business problem or problems emerging inside Microservices itself. The opposite approach to Microservices is called Monoliths – an All In One Big Service, shortly is what mostly systems nowadays are, composed from a single set of a API server and a database. Switching to Microservices, technically, is to divide functions of One Big Service into multiple small services running independently, wire them together and then we can choose fittest technologies for each small service. Each technology here can exist as a programing language, a framework, a software, a third-party service, or a tool.
The simplest form of a Microservices system, we can think it is composed from multiple Monoliths system. Each Monoliths system contains its own server & database and exposes its own API gateway . Monoliths systems communicate to each other by call APIs of others directly or listen to a shared event channels, depends on use cases.
Microservices is NOT a new skill set. Microservices is composed from multiple Monoliths services, so to do Microservices, developers must good at building Monoliths first.
What problems do Microservices solves and NOT solve ?
There is a reason that every bosses want to move to Microservices that is they think it is good. But I think not everyone understand WHAT it is good for. Microservices is NOT a pure better design than other designs. It is an adaptation to overcome problems emerging when a system is growing to big and huge size, in both manner of traffic and logic complexity. So if your system does not suppose to be the next Amazon or Netflix, Monoliths design is fine for you since it is much simpler to set up and maintain. A few thousand users with few hundred connection per second is in capability of mostly technologies nowadays, such as Spring or Node, Ruby on Rail or PHP, etc. But it is hard to estimate the threshold because each system has different features and the best way to find out it maximum capability is to do the stress test – basically to send as much as possible requests then analyze the response time. When you know your system capability, you will have a reference in number to decide when to move to Microservices. Microservices is a journey, only carry on when you are well prepared.
Microservices does NOT magically increase the system load threshold, unless the services are divided and designed appropriately. Remind that I/O processes take the main part in the delaying time between request & response. Normally, in Monoliths design, all services are on the same memory and it is the fastest way for services to cooperate to each other. But if we blindly deploy services to multiple different places to make it look like Microservices, there will be more I/O time since services have to send more requests to others that it depends on, then performance of the system will go down significantly. This may be the most common mistake when creating a Microservices system. Microservices is NOT to fan out all services to multiple servers. We must calculate to identify the bottleneck in the system before deciding to move some related services to an independent server. And it also is NOT simply to deploy current service’s source code to other server. The new server may have some beneficial points, such as a greater processing power that accelerates the service, or it is to redesign the service with other technologies that have some benefits the service needs.
A good example for redesigning the service is to separate the READ and WRITE data into two services for the same domain object (same table), the purpose is to support a large of concurrent reading/writing data with low latency. Assume that we are having a Monoliths system but after a period of growing, we have a very huge data amount and complex data schema on a SQL database so that every time a query is issued, it freeze the whole system for a few seconds. This is bad and we want to improve. That moment, we may come to this solution: We will divide the service in READ & WRITE aspect. The READ data service may use a NoSQL database as a persistence storage but with fast reading speed to reduce user’s waiting time. The WRITE data services may use an in-memory database such as H2 to proceed data updating as fast as possible, then gradually synchronize in memory data to the persistence storage of the READ service. Those two services should run on different machine to be able to maximize resource usages. And this is a truly story of Microservices. If we simply deploy another identical service on another server to handle more traffic by routing traffic by IP or by zone, it is the term of Load Balancing.
Microservices is NOT to reduce development cost. In fact it increases. Firstly, we need more machines to run independent services, as well as more machines to run other monitor tools. Microservices is an architectural design approach, it is the view of the whole system, NOT on how each service coding solution. It does NOT magically reduce bugs. You may read here for more understanding about the source of bugs. But when services are divided well, it does enhance the boundary between services, so that can help developers to avoid using wrong components as well as to avoid creating too much cross-cutting concern components with many hidden logic. Microservices brings the real need of DevOps positions, who will take responsibility to deploy multiple services as quick as possible to ensure lowest down time between deployment. They obviously will have to create some CI/CD system to automate the deployment process, calculate system load and create/install monitor tools to keep track how services are doing with other. When a bug happens inside a Microservices system, it is more complicated to fix than in Monoliths since now there are more than 1 places to figure out what is the truth source of a bug. Developers also always have to set up an identical system on their local machine for developing and testing. A system of multiple services requires stronger machine for developers. Too many services system can be somehow impossible to deploy on a single machine and we may need some Mocking technique to create fake API gateways on behalf services. Writing automation tests gets harder too, etc. And many many behind the scene works like these will disturb developers when switching to Microservices. More work, more job, more salary.
Microservices is NOT to freely apply latest technology. I bet that your team won’t want to work in a tech-soup. Agree that Microservices open us an ability to mix multiple technologies to make use of their advantages. But remember that it does require us to understand their advantages before applying, or your system will get more complexities without any significant benefit and crying is coming soon. Microservices is NOT only about technology, it’s also about human. It may depends on how your team is organized, what their skills are, what they are good at. Because learning some new things does take time and if you are in rush, let do with tools that you are familiar. Example we are about to create a small service to handle Employee’s documents in 1 month and we are having only 1 thousand employees. Our developers are experts at Java but Go is the new language and it is on trending. You may hear somewhere that “Go is faster” but here is the point, your developers will build that new service faster with Java than Go and that one thousand users is not the limitation to have to switch from Java to Go.
Microservices is NOT to create boundaries between teams. It is to create the boundary between services that your teams are creating only, technical boundaries only. The more developers know about other services, the more chances they find out problems early and the less communication cost between teams. Don’t use the architectural design as a political tool inside an organization. One developer can work for multiple services depends on his/her ability. Those people usually act as an important bridge between services. I know that some managers want to divide teams to rule easier, but I feel it is not a good way to create an organization: people will go to work with doubts and envies because much or less, all services are necessary at some points but at each moment, some are important than others. Non-boundary teams also activate cross-checking that can push teams move forward, also reduce job security. No sharing, no checking between employees will gradually hint a few ones to think that they are irreplaceable. It is a toxic thinking for an organization.
So when to go Microservices ?
Microservices do not help to reduce costs, not help to improve performance, not help to be “better”, so why do it is on trending ? Because it is from big tech companies, and people tend to believe what come from big boys always “better”. We easily blindly copy without diving deep to understand why they do that. With big tech companies, they hit the limitation of technologies and a single Monoliths system can’t help them anymore so they have to use multiple Monoliths to solve problems. And the result is a system that they named Microservices. Technology changes everyday and who know what will come in next few years. We see many frameworks, languages, platforms come as “better” options then die. So the key point to decide to move to Microservices is to know the limitation of current system by testing the load well.
Another reason we might need the Microservices is to implement many projects at the same time. Example we need to build a Pricing Engine module in the same time with an ERP module to manage employees, we might assign them for 2 teams since the business logic of modules does not depend on other. Each team can develop their own service on separated server so the deployments of each service is independent too. If 2 modules is built into 1 Monoliths service, an issue happening on a module may block the whole deployment process to prevent risks happening on production environment. So the key point when dividing services for teams is the dependency between services. They should be loosely coupled. It means each service can act as a separated product without knowing or need existence of other services.
When each service is truly independent, it can be reused too. Example your companies has multiple projects but using the same employees for all projects, so to avoid duplicating features like authentication, employee manager, or full text search service, etc, we can carving them to separated services that can be reused by different projects.
One scenario that you can find out your system look like Microservices, is when to rewriting the legacy system with up-to-date technology. Rewriting the whole system is time consuming so we usually have to rewrite module by module. Each rewritten module can be deployed at a separated server and on the way of rewriting the legacy system, you are using Microservices.