Composable architecture is a modern approach to web and application engineering that puts emphasis on the use of multiple highly-specialized, modular components to satisfy business requirements. In contrast, a traditional monolithic approach would seek to utilize as few components as possible within a stack, usually at the expense of the applications' specialism and ability to satisfactorily accomplish specific tasks, which are often nuanced.

Traditionally, business decision makers would select software based on its ability to fulfill multiple needs or requirements. The idea was that maintaining a single application, or just a few applications, would result in lower overhead for the business and more predictable experiences.

In short: Monolithic architecture dictates the usage of as few technologies as possible, usually just one, which is responsible for executing a number of tasks and business logic.

Composable architecture, on the other hand, comprises multiple (essentially limitless) modular components which are highly-specialized to execute a particular task. These components are then connected to each other via APIs, allowing them to transfer and consume data between themselves, taking the appropriate action and returning the desired result.

By definition, composable architecture involves significantly more moving parts than a competing monolithic approach. But you'd be forgiven for assuming that composable stacks require greater levels of maintenance: it's actually the opposite which is true.

The beauty of composable architecture is that, while many components are present throughout the stack, each one is isolated and specialized at accomplishing a particular task. In production, this makes composable architecture highly nimble, infinitely more scalable, and thus easier to maintain.

The terms "modular" and "component-based" are frequently associated with composable stacks, and for good reason. These tech stacks boast the ability to deliver powerful experiences and fulfill highly-custom domain logic, whilst allowing businesses to react with more agility to changes in their respective commerce landscape.

Benefits of Composable Architecture

Through greater composability, businesses are able to implement a number of best-in-class components to a tech stack which are independent and highly-specialized. This achieves a few things:

1. It takes out the guesswork

Stacks which have been architected in a composable way are more reliable, specialized, and nimble. This takes out the guesswork for businesses by providing an system which, as a whole, has been designed to satisfy at-the-time requirements, but remains widely customizable at the point of each implementation. Ultimately, this provides a business with the ability to refine or reimplement individual components of the system as requirements and logic changes into the future.

With a composable approach, a business can be sure that the stack will remain constantly adaptable in times where rapid change is required.

2. It reduces dependency headaches

Monolithic systems are tasked with the fulfillment and execution of broad requirements and are most often tightly-interwoven with business operations. This makes for a fragile architecture upon which many expectations rely.

Because code within traditional monolithic systems is so tightly bound, small changes have the ability to inadvertently break other parts of the system, which can have a ripple-effect throughout the whole of its implementation and cause unexpected failure and breakdown. Put simply, the entire application is liable to break due to a single line of untested or poorly executed code.

In contrast, composable architecture denotes the usage of various modular components, each responsible for the execution of a specific task (commonly referred to as microservices). In the event of failure of any one component within a composable stack, the other components remain unaffected, continuing to execute the actions and jobs for which they have been tasked. This modular nature also permits the teams and developers the ability to rapidly identify where issues lie, expediting the time in which they can be resolved.

3. It allows better technology selection for individual components of the stack

With composable architecture, each modular component or microservice can be developed using best-fit technology that either significantly enhances the service's ability to execute its requirements, or vastly expedite its overall development time.

This empowers both businesses and development/implementation teams, as the most appropriate technology can be selected for each specific use-case.

In contrast, a monolithic approach will often aim to satisfy as many requirements as possible within familiar parameters: namely a single (or very few) programming languages, a single server with resources that are shared across the entirety of the system, and a principle development methodology.

This is a poor choice of implementation for various reasons, but namely it does not allow the appropriate selection of technology depending on any particular service or requirement of the many the application may be tasked with.

Programming languages, server environments and development methodology all have their strengths and weaknesses, and a monolithic all-in-one approach isn't able to cater to this demand.

4. It promotes a greater degree of flexibility in terms of microservice implementation and the methods used within

Composable architecture promotes a high degree of flexibility from various angles. 

For decision makers, it allows finer tuning of requirements and business logic for specific and targeted microservices, providing a greater level of focus and demanding more critical thought processes. 

At the same time, decision makers are able to tweak and revise domain logic and requirements for individual components and microservices in the future without the fear of introducing undesired complexities to other areas of the stack or application.

In terms of development, a composable approach provides a fluid and adaptable means of implementation, whereby technology can be selected on a best-fit and per-service/component basis, enabling microservices to best fulfill targeted requirements.

This helps to alleviate situations where inappropriate technology selection is hindering performance and efficiency of a technical implementation.

5. It leads to a healthier tech stack which is less likely to suffer from the perils of technical debt

"Technical debt", or simply "tech debt", is a complication which can arise as a result of mis-management of a tech stack or application architecture. 

The term simply refers to a situation whereby business resources are lost unnecessarily to servicing or employing the use of a software (or indeed an entire stack) on an ongoing basis. 

Such software is usually critical to the business operations, which is the primary reason why organizations find themselves in a position of technical debt.

Such a scenario typically comes about because the stack was either ill-designed for its current purpose, or has been subject to repetitive low-level "life support" for a prolonged period of time, usually in the form of "hacky" quick fixes. 

This is often due to—perhaps quite ironically—a business's reluctance to spend sufficient resources on modernization or adequate maintenance of the stack. 

It can also come about from over-utilization of legacy software/stacks that have not received the necessary modernization over time.

By modularizing a system through the use of microservices and individual components, a system's maintainability as a whole can be drastically improved and made significantly more efficient. 

By breaking up your system's architecture into more manageable, independent services, it becomes possible to target individual components more easily and without wider dependency issues. 

With a composable approach, it's possible to make highly-targeted additions to microservice functionality, update select code or dependencies, conduct reliable testing, and refactor individual components rapidly at will.

This acts to supercharge productivity not just for development teams, but for the wider business as a whole.

As a result, the business is better able to avoid the costly implications of technical debt, which is a common phenomena within monolithic system architectures in particular.

6. It leads to easier maintainability

Similarly to a megastructure, monolithic architectures are highly-involved and cumbersome to maintain. 

They lack the ability to be agile by definition, and have a high number of self-perpetuating dependencies.

This makes them unsustainable for many businesses over the long term, requiring vast amounts of delicately-performed servicing and maintenance in order to ensure smooth operation.

Software or server-side upgrades have the potential to break an entire monolithic system, putting the efficiency of business operations at risk.

In contrast, an alternative approach which leverages composable architecture facilitates an easier maintenance cycle, due to the fact that individual components can be serviced, upgraded, and maintained independently. 

As this occurs in relative isolation, other components within the stack are unaffected. 

This means that specific microservices can be iterated upon and undergo routine maintenance more reliably, whilst significantly improving a development team's ability to pinpoint potential issues and resolve them faster.

The individual codebase of a single microservice will look vastly different than an entire monolithic application, and so it's easy to see how a single microservice could be serviced and maintained much easier on its own.

7. It prevents total breakdown of the wider system

Due to their highly-modular nature, stacks which have been architected in a composable way are naturally less fragile than an alternative monolithic approach.

This provides an array of benefits to disruptive organizations who seek to lead in their space. Notably, though, composable stacks help to ensure a greater level of system-wide stability and predictability.

There are many moving parts in a composable build, but each of these individual components is autonomous and contains relatively less moving parts when compared to the alternative of housing them all within a single service or application.

As a result, systems are more secure and reliable. 

In a worst-case scenario where one component experiences breakdown, the remainder of the stack continues to operate as expected, and the impact of the isolated breakdown is mitigated against significantly.

By contrast, a single line of code within a monolithic architecture can potentially (and often is) responsible for a system-wide breakdown, which can wreak havoc in highly-trafficked production environments.

The modularity of composable architectures works to expedite a developers' ability to pinpoint and subsequently resolve issues and bottlenecks which would have previously been considered zero-day disasters in an alternatively monolithic technical infrastructure.

8. It leads to a stack which is more competent at satisfying nuanced logic and business goals

A key factor that distinguishes good software from great software is its ability to expertly accomplish a given task with efficiency, accuracy, and reliability.

A composable architecture approach to building a tech stack helps businesses to achieve this, through the development and use of highly-specialized, targeted microservices which are purpose-built or selected for their ability to accomplish a specific task.

In the case of purpose-built microservices, each one can be engineered with a narrower set of requirements that fosters appropriate technology selection and methods of implementation. As for external services and tooling, a composable approach to stack or application architecture provides a business with greater flexibility in vendor or technology selection.

This combination of internal, purpose-built microservices and best-in-class external integrations fuels a composable stack's ability to deliver on a more nuanced business logic and complex functionality.

In selecting the best possible technology and means of implementation for each specific component within a composable stack, the system's ability to satisfy business requirements is more achievable and in many cases actually easier to implement.

9. It allows a business to "plug-in" additional components within the stack at will, and to also retire components no longer servicing the company

One of the key differentiators of a composable stack that they possess an innate agility when compared to a more traditional single-service approach. 

A composable stack is not bound by the limits of its current microservices or their implementations, and remains adaptable by design.

Individual components within the architecture can be effectively "switched out" at any time, such as where a particular integration proves to be no longer the most suitable or fails to meet the evolving needs of a business.

The integration of new functionality or integrations isn't confined to the existing capabilities of the stack, and this effectively allows a business to plug in additional components to the stack as the need arises.

This has a particularly positive impact in markets that are highly volatile or frequently evolving, by facilitating the business's ability to react to changes in requirements, business logic, or user preferences.

10. A composable stack allows for better oversight and aids a business to identify individual components which are underperforming

Because they're so modular, a composable approach provides greater transparency and helps to improve understanding of a system. 

It's far easier for a business to determine which components of a stack are underperforming, or indeed over-performing, when they exist as independent microservices or components.

With composable, it's easy to identify where challenges may exist and generally faster to devise and implement solutions aimed at better fulfilling the requirements as intended.

Headless architecture vs Composable architecture

In the context of web, application and systems development, there is a lot of overlap between composable architecture and headless architecture. The two terms come into close contact and will be used frequently together when it comes to software.

Headless-first development will often feature largely as part of a composable web architecture. However, while they're related, they aren't synonyms for the same thing.

In digital, the term "headless" is used to describe a development approach whereby an application's frontend interface is decoupled from backend systems, with the two connected via a series of APIs.

Composable architecture, on the other hand, is more of a system design principle that dictates the usage of individual, modularized components which come together to form a whole system.

All headless implementations by design implement some form of composability: at least two independent components will exist within all headless builds, and these will be connected via APIs. However, to what extent a headless build is truly composable is wholly dependent on its implementation. It's entirely possible for a headless build to be overly-reliant on fewer, less specialized components (less composable), or heavily integrated with a number of highly-specialized, best-in-class components and microservices (more composable) that allow the system to better achieve its requirements as a whole.

How APIs fuel composable architecture

Composable architecture is a forward-thinking systems design principle which involves the use of various highly-specialized modular components to form a tech stack. In composable architecture, these components can either be purpose-built (microservices) or carefully selected third-party frameworks and libraries (integrations). When these individual modules are brought together, they form a complete tech stack which is designed to fulfill business requirements in an efficient and customizable way.

The role of an API is to facilitate the passing of data between two different systems, which is why they form such a critical part of a composable build. APIs fuel the integration between components in a composable tech stack, allowing them to both consume data and return it.

For microservices, APIs can be custom-built and architected to provide specific sets of data, in order that we are returning only what's required—but enough that it is useful to the recipient service. In addition, data can be transformed as required before it's returned through the API in order that it can be consumed as efficiently as possible wherever it's received. Beyond APIs, webhooks will often form a key component to composable architectures too. Webhooks are essentially "notifications" which are dispatched from one service to another, allowing certain actions to take place on receipt of the data.

Composable vs Monolithic architecture

Composability is all about modularization. 

As an approach to engineering of a tech stack, software, or other application, this introduces fluidity and agility. 

A monolithic approach to stack architecture, on the other hand, is best placed where long-term rigidity and its associated predictability is desired. 

However, for most businesses who operate heavily in digital markets, agility is more often required. 

The increasingly heightened pace of innovation in the digital landscape is such that firms who seek to position themselves as disruptive require a high level of agility in order to sustain this.

In an ever-evolving digital landscape, it's never been more important for businesses to be agile and adaptable. 

Regrettably, monolithic application architectures are neither of these things.

While there's certainly a use case for monolithic systems design, it's not best placed for businesses who seek constant innovation and agility, particularly where web-based systems are concerned.