Headless CMS architecture pattern

In recent days I have come across a new term going around whilst investigating new alternatives for our current CMS architecture. CMS systems have been around for many years and whilst they have served their purpose in being able to add, update and deliver data to customers, they were designed primarily for desktop devices. With the advancement of mobile and other devices, it has become increasingly important that a cms solution be able to cope with this advancement and also account for scalability issues that one may face.


What does Headless CMS provide?

Headless CMS provides a back end only CMS system that is built with a content system and exposes a Restful API that is responsible for displaying data onto any device. With this approach it presents a presentation agnostic approach to delivering data and doesn’t tie any particular presentation to its backend.


What is in a traditional CMS?

  • Provides a method to store and maintain data.
  • Provides a CRUD UI
  • Provides presentation layer to display the data.


What is in a headless CMS?

  • Provides a method to store and maintain data.
  • Provides a CRUD UI
  • Provides Restful API to the data.


Why decouple CMS?

With traditional monolithic CMS systems the content management application and content delivery application exist together in a single application, they provide a solution for simple blog and basic websites where everything can be managed in one place.

With a decoupled CMS, we are able to separate the content management application from the content delivery application, this frees up developers to be able to choose the way they want to deliver content to users. It is important to understand that the creation of content is not the same as delivering and that the separation are clear.

In a decoupled CMS, it promotes the microservices architecture approach and you can leverage the use of event driven message queues in order to store state for content and updates to the website. By using the event driven approach when you delete a content element, then there is a call to the contentdelete event.

Event consumers will be responsible for consuming the changes produces by the event source that handles events and can be optimised through the API.


What would an architecture look like?


For a headless CMS system, we could deploy something based upon CQRS:-

CQRS stands for Command Query Responsibility Segregation. It's a pattern that I first heard described by Greg Young. At its heart is the notion that you can use a different model to update information than the model you use to read information.

From: Martin Fowler


Utilise event sourcing:-

Create an approach that is responsible for handling a sequence of events on as operations on data where each event is appended onto a read only basis to temp or permanent store. When a action takes place, the application sends a series of sequence command operations that once stored can later be replayed when executing the same series of operations on the set of data.

Heres a brief fact sheet of what it performed with event sourcing:-

  • Events are immutable
  • Task produced can run in the background
  • Improve performance and stability as no contention for processing of transactions
  • Events represent what events have occurred.
  • Append only nature to the data means that an audit trail is provided, can replay events at any time.
  • Decouple task from events and provides flexibility and extensibility.

There are however a few issues that also need to be considered:-

  • Some delay when adding events to the event store between the handler, publishing events and consumers handling the events.
  • If you need to undo a change to the data is to add a compensating event to the event store


You can read more about it here.