from the adapters. So how do we “publish” an interface (the port) of a module (the hexagon)? One major appeal of using hexagonal architecture is that it makes your code easier to test. If we wanted to be concrete about it, rather than abstract, we’d say “Call Johnny using the following procedure: Turn on your phone; tap the phone icon; now, tap the following numbers on the screen: 555-5555; tap send….” I won’t bore you with any more details. The name of a package for a port will be: This way ports are grouped by their side (driver/driven), so that we see at a first glance whether the port is driver or driven. You can run the application by running any of the driver adapters, so there will be a package for each driver adapter, containing the source code needed for instantiating the different components of the architecture, wiring them up, and running the driver adapter. The following four interactions between the tests and the application will happen via ports: The tests and the test doubles (such as mocks, fakes, and stubs) drive the application through the ports. to the hexagon. For example, I see two architecture styles we can implement the pattern with: The modular diagram is similar to an UML component diagram. Hexagonal Architecture is a type of architecture that is based on the principle of Ports and Adapters. The adapter is the implementing class of the IUserRepo. Thanks for this nice wrap up. All our UserAdmin object knows about is the Save method on whatever the _userRepo references via the interface. Imagine a hexagon shape with another, larger hexagon shape around it. It publishes (exports) the packages with the ports. Thanks. Now we need to pass this FakeUserRepo adapter to the UserAdmin in our test code like this: You can see that this test code is passing the FakeUserRepo into the UserAdmin class using its constructor. The sides are simply representations in the model for ports. In this example, the Save method uses the IUserRepo interface. My vision of Hexagonal Architecture is modular, with the hexagon at the center, and adapters around it, belonging to no layer, each one attached to a port of the hexagon. Here’s where our adapter comes in. In doing so, you isolate the central logic (the core) of your application from outside concerns. The goal is to make the application easier to test. This is how the message is either handled or passed along. Although hexagonal architecture seems like some vague mystical concept from the ages, it’s actually widespread in modern software development. Download the NDepend Trial and understand your .NET code base technical-debt within a few minutes. Alistair explains that the authors “call [the ada… The whole project is structured in modules. Great article. It’s possible to use dependency injection and other techniques in layered architecture to enable testing. In Java 9, ports are interfaces into packages that the hexagon module publishes to other modules. Photo by Ilnur Kalimullin on Unsplash … Came up when I searched for ‘hexagon’. An adapter depends on the hexagon at one of its ports. An adapter doesn’t know of the others, it just depends on the hexagon, and on the actor whose technology it is adapting (for example a database). Remember that hexagonal architecture is a model for how to structure certain aspects of the application. In hexagonal architecture, a port—much like an interface—is an abstraction. Regarding Java 9 modules, I highly recommend the book “Java 9 Modularity: Patterns and practices for developing maintainable applications”, by Sander Mak & Paul Bakker. I’d add that another advantages Hexagonal Architecture for testing is that we can reuse almost all the in-memory fakes for all the tests. It fits like a glove as the primary port (API of the hexagon) of hexagonal architecture. This is the biggest benefit of hexagonal architecture! Hexagonal Architecture ,also known as Ports and Adapter pattern is an architectural style which promotes and gives structure for achieving separation between actual application / domain logic and various technology concerns and external actors.Alistair Cockburn has a detailed articleon this architecture style and below is short definition from the same article. In this chapter we will see how to organize the source code in modules using Java 9, dependencies between modules (“who knows of whom”), and how to configure those dependencies. A port can represent things like the user, another app, a message bus, or a database. You could even use files and scripts to drive it instead! How would you suggest to implement it? The hexagon module would look like a component where driver ports are “provided interfaces”, and driven ports are “required interfaces”: These two layers would be in fact three, since the startup module can be considered here as another layer on top of the outside layer. Simon is an independent consultant specializing in software architecture, and the author of Software Architecture for Developers (a developer-friendly guide to software architecture, technical leadership and the balance with agility). Cockburn explainsthat t… He writes about topics relevant to technology and business, occasionally gives talks on the same topics, and is a family man who enjoys playing soccer and board games with his children. In Java, we have the default access modifier (package-private), which makes a type visible to just the members in the same package. The bottom line is that you don’t need to rely on external factors to test your application. In the example above, the module host would inject the IUserRepo into the UserAdmin class. But there’s a key difference in the hexagonal model: The UI can be swapped out, too. There are no specific requirements about the core, just that all of the business/application/domain logic lives there. Publisher: O’Reilly. But what does that look like, you ask? We don’t care how you tell Johnny so long as he gets the message. Hexagonal architecture is all about swapping components—specifically, external components. The latter name, Clean Architecture, is used as the name for this architecture in … Unfortunately in my previous experiences in different companies, remain very common that applications are built on top of frameworks and … But the "hexagonal architecture" name stuck, and that's the name many people know it by today. This is because it has the concept of different ports, which can be adapted for any given layer. Before Java 9, a public type was visible to the rest of the world. ). An adapter module for a port, requires the hexagon module, and other modules related to libraries and frameworks, according to the technology that the actor behind the port is using. This is why if we go for the two layers implementation, we should care about protecting visibility between adapters, since a layered architecture allows a component to access other components in the same layer. I’ve already enumerated the advantages of using hexagonal architecture in your design. But the “hexagonal architecture” name stuck, and that’s the name many people know it by today. That’s much easier to notice than if everything were in one .csproj, where I am one “using” statement away from breaking the architecture. The interface is in the language of module A. Alistair Cockburn uses to name the hexagon as the “App” … The outside part is UI, database, messaging, etc. This is quite different from the typical approach to mocking, which tends to multiply test-specific mocks… and bring us in mock hell. So it is not layered “per se”, it is not component-based (modular) “per se”, etc. The hexagon is decoupled from any technology, i.e. You can implement it using any architecture style, as long as it fits the structure and relationship rules of the pattern. Test doubles receive output from the application. Hexagonal architecture was proposed by Alistair Cockburn in 2005. In this post, we’re going to take a look, in detail, at just how hexagonal architecture works. Alistair explains that the authors “call [the adapter] stereotype ‘Interfacers,’ but show examples of them using the GoF pattern ‘Adapter.'”. The adapters aren’t the database and the TCP port; rather, they adapt the message from the port to its destination(s). Tests receive output from the application. At either driver or driven side, the Configurable Dependency Pattern applies as follows, quoting Alistair Cockburn in his “Alistair in the Hexagone” talk: The one who does the triggering has to know the dependency. The pattern definition doesn’t say anything about how to implement the architecture. Hexagonal architecture was proposed by Alistair Cockburn in 2005. This architecture has gone by many names over the years. The example application is called BlueZone, and it is described and designed in Chapter 1. In .NET-land, a web UI would interact with the UserAdmin class through an HTTP endpoint (the port) and ASP.NET Web API (the adapter). So, we have this interface (as a port). Now let’s see the modules and the convention I follow for naming them and their packages. But an adapter shouldn’t be able to access another adapters. I’ve put all the modules in just one GitHub repository, so that you can see and build them all together, but Java 9 allows you to have them in different repositories, compile them apart, and then provide their locations at runtime to choose them dynamically. Any team implementing such a solution will almost certainly require an expert to drive the solution and keep it from evolving the wrong way and accumulating technical debt. So what are ports anyway? We don’t need to, since that’s something that comes with the port. Now we need to make that message talk to something else. Whatever approach you choose, there are some key concepts to consider for fitting Hexagonal Architecture pattern rules, which make it different from Onion: Ports are not a layer themselves. We isolate the boundaries by using Ports and Adapters. Here’s a concrete example using some C# code. For example our framework will "adapt" a SQL "port" to any number of different SQL servers for our application to use. But we would have to change this file and recompile the hexagon, every time we add a new adapter. This is the second article of a series showing how to implement an application according to Hexagonal Architecture, also known as Ports and Adapters pattern, whose author is Dr. Alistair Cockburn. * Depends on all the other modules: hexagon and adapters Include IL Offset into Production Exception Stack Traces. Thirteen years after Alistair’s idea, we commonly use the term “interface” without remembering how the world was without one. "Hexagonal architecture" was actually the working name for the "ports and adapters pattern," which is the term Cockburn settled on in the end. The main theory behind it is decoupling the application logic from the inputs and outputs. ASP.NET Core is a new web framework that Microsoft built on top of .NET Core to shed the legacy technology that has been around since .NET 1.0. My vision of Hexagonal Architecture is modular, with the hexagon at the center, and adapters around it, belonging to no layer, each one attached to a port of the hexagon. As an example, the simplest way in Java to implement a hexagon would be just one class, implementing driver port interfaces, and depending on driven port interfaces (constructor arguments). We will see this later on, at the end of this article series, as an advanced way of execution. The other name of Hexagonal architecture is Ports And Adapters architecture. Our module can use the interface to send messages. Hexagonal Architecture, also called Ports and Adapters Architecture is separating the input-output API from the user interface or other 3rd parties, … So you should have a package for each adapter, and make types in each package not accessible from others, i.e. After all, the main goal of decoupling through ports and adapters is to test-drive the application using software (a test harness). An interface defines how one module communicates with another. By comparison, ASP.NET 4.6 still uses the System.Webassembly that contains all the WebForms libraries and as a result is still broughtinto more recent ASP.NET MVC 5 solutions. Is Artificial Intelligence Assisted Coding the Next Developer Productivity Silver Bullet? The idea behind it is to put inputs and outputs at the edges of your design. It was coined by Alistar Cockburn more than 13 years ago, and this received improvements with the Onion and Clean Architectures. Hexagonal Architecture pattern says nothing about how to structure the source code of the hexagon. There’s a bit of interesting trivia about its origins. DDD bullet points – St. Louis area developer. Hexagonal architecture was a departure from layered architecture. Visual Studio IntelliCode : AI Assisted Coding. I have been using a layered approach for years now serving multiple channels with one core application/domain. Hexagonal architecture is a model or pattern for designing software applications. This architecture divides an application into two parts namely, the inside part and the outside part. But how does this help my code, you’re wondering, and what does it have to do with hexagonal architecture? Exporting a package would be like “publishing” its public types to the outside world. Anything goes so long as the adapter responds accordingly. In this article I will discuss Hexagonal Architecture. I also added a very rudimentary way to check the List. And this was the primary motivation for the creation of hexagonal architecture in the first place. */, /* Apply Configurable Dependency Pattern on driver side: Instantiate a driver adapter, which knows of the driver port of the hexagon. Figure 2: Ports packages in hexagon module. A FakeUserRepo might look like this: This is a fake because it stores the data in memory in the List. This architecture follows the premise of guaranteeing the total abstraction of the domain with respect to all the dependencies we may have (repositories, frameworks, third-party libraries, etc. Improve your .NET code quality with NDepend. The code base of the example application is at BlueZone GitHub repository. The point is to make the core independent of its inputs and outputs. The name hexagonal architecture comes from the way this architecture is usually depicted: We are going to return to why hexagons are used later in this article. The hexagonal architecture was invented by Alistair Cockburn in an attempt to avoid known structural pitfalls in object-oriented software design, such as undesired dependencies between layers and contamination of user interface code with business logic, and published in 2005. This architecture pattern says nothing about the structure inside the hexagon, it can be whatever you want. In C#, they’re interfaces. Alistair chose this flat-sided shape instead of a circle to convey a specific intent about ports. Dependencies are going from User-Side and Server-Side to the Business Logic. The packages it “publishes” (exports) to other modules. But it got me thinking on how to implement transactions. Finally, the adapter is where we want to think about the concrete implementation. Instead, just make the core of the system interact through ports. It’s not as if there are six—and only six—ports in the hexagonal architecture. This architecture principle was created by [1] Alistair Cockburn in 2005. We could be more specific and say more about the technology. Test doubles return input to the application. It’s specifically about dealing with I/O. But the “hexagonal architecture” name stuck, and that’s the name many people know it by today. Hexagonal Architecture (aka Ports and Adapters) is one strategy to decouple the use cases from the external details. (*) bluezone-parent is a maven configuration module, nothing to do with a Java 9 source code module. Modules depend on each other. This provides a few more directions in which you can take your design. A package for a port contains a public interface defining the port operations, and public data types that those operations manage. Let’s say the _userRepo represents module B in our earlier example. The pattern just says that the hexagon offers “ports” to the outside world, for allowing external actors to interact with the hexagon. form of application architecture that promotes the separation of concerns through layers of responsibility One of the reasons for creating this pattern was mainly to delegate the infrastructure and UI part of the project, focus on the business rule and make it functional, in addition to not mixing it up, that is, a business rule in the database or even in the UI part of a project. In Java, this is achieved by using generic types. Measure quality with metrics, generate diagrams and enforce decisions with code rules, right in Visual Studio. Usually, I’d put that on my service, but doing so I’d be putting a infrastructure detail inside of my business. Once the basic structure is defined, I can’t violate the hexagonal architecture unless I add a project reference or a NuGet package inappropriately. Alistair Cockburn changed the terminology from “hexagonal architecture” to “ports and adapters.” Thankfully, hexagonal architecture sort of stuck. In Java 9, a module is a set of packages, that you can compile apart generating a jar file. In our example application, we are going to develop 2 adapters for each port: The root package for the source code of an adapter would be: This module is the entry point to the application. The important thing with this way of naming modules, is that when we see a module name at first glance, we know whether it is business logic or it deals with real world technology, since the first word after the application name is either “hexagon” or “adapter”. io.github.jmgarridopaz.lib.portsadapters module is a library of my own, where I define types regarding hexagonal architecture. no matter the technology of the actor that is behind the port. The inside part is use cases and the domain model it’s built upon. Cockburn had his "eureka moment" about ports and adapters after reading Object Design: Roles, Responsibilities, and Collaborations by Rebecca Wirfs-Brock and Alan McKean. Download the NDepend trial for free and see if your actual architecture matches your design documents. The hexagonal architecture is based on three principles and techniques: Explicitly separate User-Side, Business Logic, and Server-Side. The center hexagon is the core of the application (the business and application logic). Where it leaves you is to write the adapter code into the controller. The test runner, in this case, is the host. make them package-private. * DEPENDENCIES: Hexagon, libs, test framework For example, a driver adapter is a generic class with one type parameter, which is the driver port interface that it uses. A usual way of structuring the hexagon is to split it into two layers: application and domain, following DDD (Domain Driven Design) rules, but this has nothing to do with Hexagonal Architecture. Alistair had his “eureka moment” about ports and adapters after reading Object Design: Roles, Responsibilities, and Collaborations by Rebecca Wirfs-Brock and Alan McKean. This module configures the dependencies between the hexagon and the adapters, applying the Configurable Dependency Pattern at both driven and driver side, following these steps: Here is a hand-drawn diagram I made once about this topic: Figure 3: Dependency Configurator in Startup Module, I offered this picture to Alistair Cockburn, who published it on Twitter: What makes it possible to run a user interface, whatever type of user interface it might be; 2. This is where he really sought to differentiate his approach from layered architecture. Hexagonal architecture is a model ofdesigning software applications around domain logicto isolate it from external factors. The port of the hexagon is either driver or driven, and so will be the adapter. In hexagonal architecture terms, the interface is the port. Module A is the UserAdmin class. More recently, it's been cited as the Onion Architecture or Clean Architecture. The hexagonal architecture, or ports and adapters architecture, is an architectural pattern used in software design. Hexagonal architecture is shared into 3 parts: Hexagon center is an adapter for an actor that interacts with port using a web UI. This is the power of the adapter! The main feature of “Hexagonal Architecture”, as opposed to the common layered architecture style, is that the dependencies between our components point “inward”, towards our domain objects: The hexagon is just a fancy way to describe the core of the application that is made up of domain objects, use cases that operate on them, and input and output ports that provide an interface to the outside world. The different adapters depending on a port stand for different swappable technologies that the actor communicating with the hexagon might use. https://twitter.com/TotherAlistair/status/1122918489558278145. It builds the application and runs it, so it needs access to all modules: hexagon and adapters. And each side of the hexagon represents the ports. It will be a set of Java classes, types, etc implementing the operations defined at driver port interfaces, and calling operations on driven port interfaces. Our UserDatabaseRepository and UserHttpRepository classes are the adapters. In the example application, the name of the hexagon module is. Abstraction just means we don’t know how something does what it does. The UserAdmin class has no idea how the _userRepo does its thing. An adapter is a piece of software playing a role (driver/driven) against a port. Rules about dependencies between modules are easy: Regarding to dependencies, in Java 9 every module has a definition file (module-info.java) where it declares: So let’s see the module-info.java file of the modules: It contains the business logic, including ports. */, “Java 9 Modularity: Patterns and practices for developing maintainable applications”, by Sander Mak & Paul Bakker, https://twitter.com/TotherAlistair/status/1122918489558278145, quoting Alistair Cockburn in his “Alistair in the Hexagone” talk. The core logic of … I start by recalling EBI and Ports & Adaptersarchitectures. Authors: Sander Mak & Paul Bakker. Each port package just publishes the interface defining port operations, and the data types that those operations manage. “Hexagonal != Layers”, by Thomas Pierrain: “The key ring metaphor: A three steps initialization” (pdf, page 11), by Thomas Pierrain. newcomer to F# might be tempted to organize code in classes just like in C# Enter the adapter. This is one of the many forms of DDD(Domain Driven Design Architecture). Hexagonal Architecture is an architectural style that moves a programmer’s focus from conceptual layers to a distinction between the software’s inside and outside parts. Having inputs and outputs at the edge means you can swap out their handlers without changing the core code. This stands for a module containing an adapter for an actor using the in the interaction with the hexagon at port. During my researching on hexagonal architecture, I’ve studied several techniques for implementing the application startup, and I will show them in detail along the next articles in these series. Ports and Adapters Pattern (aka Hexagonal Architecture), by Alistair Cockburn: My conceptual article about Ports and Adapters Pattern (aka Hexagonal Architecture): Alistair in the Hexagone: a talk by Alistair Cockburn about Hexagonal Architecture: “Configurable Dependency Pattern”, by Gerard Meszaros & Alistair Cockburn: “Java 9 Modularity” book. which has 5 packages for its ports (2 driver and 3 driven): Ports are named following the forDoingSomething pattern, saying what they are for, in a technology agnostic way from the application point of view, i.e. But first, let’s talk about why this is desirable. See more ideas about hexagonal architecture, architecture, architecture drawing. For example, the instruction “Tell Johnny to meet me at the bank” is an abstraction. To give you a common scenario of how this works in practice, let’s say we’re using a .NET testing framework such as xUnit. By modules I mean source code subprojects (e.g. The main purpose of architecture is to improve maintainability and reduce how much time one will have to spend maintaining and modifying their code in the long run. The layer between the core and the outer hexagon is the adapter layer. Notice how the UserAdmin only knows about the interface. Now, with modules, a public type is just visible inside its module. The different adapters depending on a port stand for different swappable technologies that the actor communicating with the hexagon might use. It is also possible to declare the modules you want to export a package to, so that you could export a port just to its adapters. https://web.archive.org/web/20180822100852/http://alistair.cockburn.us/Hexagonal+architecture, https://jmgarridopaz.github.io/content/hexagonalarchitecture.html, https://www.youtube.com/watch?v=th4AgBcrEHA&list=PLGl1Jc8ErU1w27y8-7Gdcloy1tHO7NriL, https://web.archive.org/web/20170624023207/http://alistair.cockburn.us/Configurable+Dependency, https://tpierrain.blogspot.com/2016/04/hexagonal-layers.html, https://github.com/tpierrain/hexagonalThis/blob/master/Hexagonal.pdf, io.github.jmgarridopaz.bluezone.hexagon.driver.forparkingcars, io.github.jmgarridopaz.bluezone.hexagon.driver.forcheckingcars, io.github.jmgarridopaz.bluezone.hexagon.driven.forobtainingrates, io.github.jmgarridopaz.bluezone.hexagon.driven.forstoringpermits, io.github.jmgarridopaz.bluezone.hexagon.driven.forpaying, // Implement the driver port operation calling driven ports operations, io.github.jmgarridopaz.bluezone.startup.forparkingcars.test, io.github.jmgarridopaz.bluezone.startup.forparkingcars.webui, io.github.jmgarridopaz.bluezone.startup.forcheckingcars.test, io.github.jmgarridopaz.bluezone.startup.forcheckingcars.cli, /* Finally, the center is the application and domain. Whether an adapter plays different roles: it drives more than one port; or it is driven by more than one port; or it is driven by a hexagon port and it drives a port of another hexagon… it’s up to you, but then you should know that you are not following the SRP (Single Responsability Principle). It’s important to note the use of the term “Interfacers” in that wiki entry because that’s really what it’s all about! Applying Hexagonal Architecture: main principles. Ports are part of the hexagon, they are interfaces that belong to the business logic of the application, i.e. With an abstraction, we only know the high-level details. It’s the left/right asymmetry . The analogy kind of falls apart there. Both of them make an explicit separation of what code is internal to the application, what is external, and what is used for connecting internal and external code. Any logic implementing the driver ports is hidden to other modules. Hexagonal architecture is an architectural style that focuses on keeping the business logic decoupled from external concerns. TL;DR: I think that from a DDD point of view, you're basically right, but in order to be an Hexagonal design, you should be able to register or expose your use-cases in your primary ports: web, console or "usage" as @chris-f-carroll suggests.. This arhictecture also goes under the names ports and adapters (which better explains the central idea behind it) and onion architecture … This makes components exchangeable at any level and facilitates test automation. Hexagonal architecture was proposed by Alistair Cockburn in 2005. Furthermore, Ports & Adaptersarchitecture explicitly identifies three fundamental blocks of code in a system: 1. For other modules to see the public type, you have to export the package the type belongs to. Philippe, that’s the benefit of the architecture: you can use in-memory, or mocks, or the real thing.