![]() The first API is Restaurant Management, which defines the Restaurant() operations. With the ISP in mind, another way of looking at the Restaurant Service is that it has two APIs. Perhaps, the same is true of services albeit for different reasons. In other words, a class should have multiple smaller, specialized interfaces rather than one large interface. It states that a client should not be exposed to methods in an interface that it does not use. Applying the interface segregation principleĪn important OO design principle is Interface Segregation Principle (ISP). The Order Service now only consumes a very simple event that contains an outcome and a subtotal.īut on the other hand, the complexity of Restaurant Service’s API has barely changed. It has no knowledge of a menu’s structure. On the one hand, the Order Service is significantly less coupled to the Restaurant Service. The Order Service uses the subtotal from the RestaurantOrderCreated event to calculate the orderTotal. In this version of the architecture, Restaurant Service’s API still defines Restaurant() operations.īut, instead of publishing Restaurant events, it publishes simpler RestaurantOrder events, which contain the outcome of validating and pricing the order. The Order Service is primarily responsible for calculating fees, taxes, yet more fees and the order total. Responsibility for storing, validating the line items and calculating the order subtotal is moved from the Order Service to the Restaurant Service. The second version of the architecture reduces coupling by encapsulating all knowledge of the menu structure within the Restaurant Service. Let’s look at an architecture alternative that has less coupling between the Order Service and Restaurant Service. The Order Service uses the Restaurant events to maintain a CQRS replica of restaurant menus, which it uses to validate and price an orders.īut one drawback, however, is that the Order Service is coupled to the menu structure.Įnhancing the application to support customized burritos requires the Restaurant Service and the Order Service to change in lock step. The Restaurant Service has an API that implements Restaurant() operations and publishes Restaurant events, which contain the restaurant’s menu. There are two versions of the food ordering application. Sometimes, however, a service doesn’t look like an iceberg.Ĭonsider, the takeout Burrito example from my 2021 QCON presentation on design-time coupling. When a service doesn’t look like an iceberg That’s because what’s hidden can be easily changed.Ī service’s API should meet the clients’ needs while hiding much of the implementation. It should be much smaller than the service’s (hidden) implementation. Its API, which consists of operations and published events, is the visible part of the service. One very helpful idea is the Iceberg principle.Ī service should be like an iceberg, mostly below the waterline. Services should be like icebergsĮnsuring that your services are loosely coupled requires careful design. While such an architectural disaster might result in conference talk about why microservices are a bad idea, it could create an existential crisis for your business and is best avoided. If you neglect design-time coupling, you risk creating a distributed monolith, which combines the complexity of the microservice architecture with the friction of a monolith. ![]() What’s more, teams need to spend much less time coordinating their work. In a loosely coupled architecture, changes to a service rarely require other services to be changed in lockstep.Īs a result, it’s easier to make changes. Icebergs, the Interface Segregation Principle and microservicesĪn essential characteristic of the microservice architecture is loose design-time coupling.
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