Integration Architecture Document

Purpose

The integration architecture ensures that system interconnections are designed consistently, reliably, and securely. It prevents point-to-point spaghetti integration and establishes patterns that teams can follow for new integrations.

When to Use

Create when the solution needs to integrate with two or more external systems. Essential during alpha when integration approaches are being decided, and maintained through beta as integrations are implemented.

How to Build

Start by cataloguing all integration points — every system-to-system connection. For each, document the source, target, data exchanged, direction, frequency, and volume.

Define the integration patterns to be used: synchronous request-response, asynchronous messaging, event-driven, batch file transfer, or API-led connectivity. Justify why each pattern is appropriate for its use case.

Specify the technical standards: API design standards (REST, GraphQL, SOAP), message formats (JSON, XML, Avro), authentication mechanisms (OAuth2, mTLS, API keys), and error handling approaches.

Document the integration infrastructure: API gateways, message brokers, ESBs, or integration platforms. Show how they fit into the deployment architecture.

Define operational concerns: monitoring, alerting, retry policies, circuit breakers, dead letter queues, and reconciliation processes.

Tips

Prefer asynchronous patterns for resilience — synchronous calls create temporal coupling.
Use an API gateway for external-facing integrations to centralise security and rate limiting.
Define clear data contracts (schemas) for each integration and version them.
Plan for failure — every integration will fail at some point. Design retry and fallback strategies.
Document SLAs for each integration point including availability and response time expectations.

Common Mistakes

Not planning for integration failure scenarios and recovery.
Using synchronous calls everywhere, creating brittle chains of dependencies.
Not versioning APIs, making it impossible to evolve without breaking consumers.
Ignoring data transformation requirements between systems with different data models.
Not monitoring integration health, discovering failures only when users report problems.

Government Context

In UK government, integration architecture must consider cross-government platforms (GOV.UK Notify, Pay, Verify, One Login) and departmental APIs published on the API catalogue. The Government Integration Hub and cross-government API standards should be referenced. Data sharing between departments requires Data Sharing Agreements and must comply with the Digital Economy Act 2017 where applicable.