Architecture patterns

Patterns are reusable shapes for building Defra services. They are early, exploratory work: starting points for discussion, not agreed designs.

There are two kinds:

Kind	What it covers	Example
Service patterns	The shape of a whole kind of service and how its main building blocks connect	Transactional digital service
Solution patterns	One recurring technical problem inside a service	File upload and scanning

A service pattern usually uses several solution patterns. The worked example shows both together.

Looking for design patterns?

These are architecture patterns: how to build a recurring technical solution. For design patterns - screens, components and user journeys - use the GOV.UK Design System and components and patterns in the Defra Digital Service Manual.

Solution patterns

Each solution pattern explains the problem, a solution that stays inside the guardrails, and when not to use it. Every solution pattern lists:

• the context - the problem and when you will meet it
• the solution, with a diagram
• the guardrails it helps you meet, so you can cite it in your ADRs and evidence
• related artefacts in the cross-government Secure by Design artefact library
• when not to use it

We model this section on the Department for Education's architecture patterns, and reuse their structure so people moving between departments find their way around.

See it all together

The worked example: apply for a licence follows a fictional Defra service through the transactional service pattern, with C4 diagrams, three sample ADRs and an excerpt from a threat model.

Infrastructure

No patterns yet. Propose one if your team has solved a problem others will meet.

Integration

Pattern	Use it when	Status	User experience	Guardrails
Asynchronous submission with an outbox	A user submits something that other systems must process, and you do not want those systems' availability to block the user.	Draft	Written	GR-API-05, GR-API-06, GR-API-02, GR-OPS-04, GR-OPS-02

Security and identity

Pattern	Use it when	Status	User experience	Guardrails
Acting on behalf of an organisation or holding	Users act for a business, a land holding or another person, and the service must check they are allowed to.	Draft	Written	GR-IAM-01, GR-IAM-04, GR-IAM-03, GR-DATA-02, GR-SEC-07
File upload with malware scanning	Users upload documents or images, and the files must be scanned and stored safely before anyone opens them.	Draft	Written	GR-SEC-04, GR-SEC-07, GR-HOST-06, GR-DATA-06, GR-DATA-09, GR-OPS-04

Data

Pattern	Use it when	Status	User experience	Guardrails
Reading from an authoritative source	A service needs shared data - customers, organisations, holdings, locations or species - that another part of Defra owns.	Draft	To be confirmed	GR-DATA-02, GR-DATA-03, GR-DATA-04, GR-API-05, GR-API-07, GR-OPS-04
Publishing open data with metadata	You hold non-personal data that others could use, and want to publish it so it can be found, trusted and reused.	Draft	To be confirmed	GR-DATA-07, GR-DATA-05, GR-DATA-03, GR-DATA-08, GR-DATA-01, GR-SEC-03

Status

Status	Means
Proposed	An idea we want to develop. Comment on it before relying on it.
Draft	Written and usable, but not yet reviewed by the Technical Design Authority.
Endorsed	Reviewed by the TDA. Following it is a straightforward way to meet the guardrails it lists.

User experience

Every pattern has three sections for designers and researchers: what users see, content to design and what to test with users. They link to GOV.UK Design System patterns and components where they exist. The catalogue shows whether a pattern's sections are written or still to be confirmed.

Contribute a pattern

If your team has solved a problem others will meet, write it up. Copy an existing pattern page, keep the same sections, and set its front matter. The contribution guide explains how.