Guides, Insights, Software

How to Build a Scalable Unified API Layer for Your SaaS

November 10, 2025 No comments yet

If your SaaS product needs to connect with other platforms, you will eventually face the same problem every modern team faces: too many integrations. Each system has its own API, authentication, and data format. Building and maintaining separate connections for every platform quickly becomes hard to manage.

A unified API layer solves this by acting as one central connection point. You integrate once, and it handles all the vendor APIs behind the scenes.

If you are new to the idea of unified APIs, start by reading What Is a Unified API and How It Simplifies Integration Across Platforms. Once you understand the concept, this guide will show you step by step how to build a scalable version for your own SaaS.

Step 1. Define the Goal

The unified API should act as a single gateway between your SaaS and all external systems. It should:

  • Offer one consistent set of endpoints
  • Handle authentication for each vendor
  • Normalize data so that all systems return the same structure
  • Manage retries, rate limits, and errors
  • Keep logs and performance metrics

Your app should only communicate with this unified API layer.

Step 2. Identify Categories

Group integrations by category. Examples:

  • CRM: Salesforce, HubSpot, Zoho
  • Accounting: QuickBooks, Xero
  • HR: Workday, Gusto, BambooHR
  • Marketing: Google Ads, Meta Ads

Each category will share the same schema, such as “Contact,” “Invoice,” or “Employee.”

Step 3. Basic Architecture

Start with a simple model.

+--------------------+
|     Your SaaS      |
+---------+----------+
          |
          v
   +------+------+
   |  Unified API |
   +------+------+
          |
   -----------------------
   |         |           |
+--v--+   +--v--+     +--v--+
|CRM  |   |HRIS |     |Acct.|
|API  |   |API  |     |API  |
+-----+   +-----+     +-----+

Your unified API sits between your application and all vendor APIs.

Step 4. Normalize Data

Different vendors use different field names. Your unified layer should convert them into one consistent format.

Example for contacts:

VendorFieldNormalized
SalesforceFirstNamefirst_name
HubSpotfirstnamefirst_name
ZohoFirst_Namefirst_name

All connectors should output the same schema.

Step 5. Create Connectors

Each external system gets its own connector module.

A connector handles:

  • Authentication
  • API calls
  • Data mapping
  • Error handling

Example directory:

/connectors
 ├── crm/
 │   ├── salesforce.js
 │   ├── hubspot.js
 │   └── zoho.js
 ├── accounting/
 │   ├── quickbooks.js
 │   └── xero.js
 └── hr/
     ├── bamboohr.js
     ├── workday.js
     └── gusto.js

This modular design lets you add new integrations without changing your main logic.

Step 6. Add an API Gateway

When traffic increases, add a gateway to handle routing, authentication, and rate limits.

+------------------+
|   API Gateway    |
| (Auth, Logging)  |
+--------+---------+
         |
         v
   +-----+-----+
   | Unified API|
   +-----+-----+
         |
         v
   [ Connectors ]

The gateway can be built with Nginx, AWS API Gateway, or Kong.

Step 7. Add Background Jobs

Some operations take longer, like large data syncs or retries. Move them to background jobs using a queue.

Steps:

  1. The client requests /sync/employees.
  2. The unified API enqueues a job.
  3. A worker runs the connector logic.
  4. The job updates the database or sends a webhook when done.

Use tools like AWS SQS, RabbitMQ, or Redis Queue.

Step 8. Use Caching and Webhooks

To reduce API calls:

  • Cache frequent GET requests in Redis.
  • Store normalized data in your database.
  • Use vendor webhooks when possible instead of polling.

When a vendor sends an update, your unified API receives it and refreshes the cached data automatically.

Step 9. Scale the System

As integrations grow, scale horizontally.

  • Deploy multiple API instances behind a load balancer.
  • Add retries and backoff for transient failures.
  • Use circuit breakers when a vendor is unavailable.
  • Track vendor rate limits.
  • Use centralized logs for visibility.
+--------------+
| LoadBalancer |
+------+-------+
       |
  ---------------
  |      |      |
+v+    +v+    +v+
|1|    |2|    |3|   → Unified API instances
+------+-------+

Step 10. Secure Everything

Because the unified API handles third-party access, follow strict security practices:

  • Use HTTPS only
  • Encrypt all credentials
  • Rotate keys and tokens
  • Store secrets in a vault (AWS Secrets Manager or Vault)
  • Restrict access with RBAC

Step 11. Add Observability

Monitor everything to maintain reliability.

Track:

  • Request success rates
  • Latency by vendor
  • Failed jobs
  • Webhook errors
  • API usage per customer

Send metrics to Datadog, Grafana, or CloudWatch dashboards.

Step 12. Full Scalable Architecture

              +-------------------+
              |   SaaS Backend    |
              +---------+---------+
                        |
                        v
                +-------+-------+
                |   API Gateway |
                +-------+-------+
                        |
                        v
                +-------+-------+
                |  Unified API  |
                | Normalization |
                |  Connectors   |
                +-------+-------+
                        |
          ---------------------------------
          |                |              |
   +------v------+  +------v------+  +----v------+
   | CRM Systems |  | HR Systems  |  | Accounting|
   +-------------+  +-------------+  +-----------+
                        |
                        v
             +--------------------+
             | Message Queue Jobs |
             +--------------------+
                        |
                        v
             +--------------------+
             | Cache / Webhooks   |
             +--------------------+

This version supports multiple vendors, background jobs, caching, and load balancing for scalability.

Step 13. Recommended Tech Stack

ComponentTool
API LayerNode.js or Go
GatewayNginx or AWS API Gateway
DatabasePostgreSQL
QueueSQS or Redis
CacheRedis
LogsELK or Datadog
SecretsAWS Secrets Manager

Step 14. Example Flow

Client -> API Gateway -> Unified API -> Connector -> Vendor API
       <- Normalized Response <-

This flow keeps everything consistent and easy to extend.

Step 15. Test and Version

Keep stability by versioning endpoints (for example /v1/contacts).
Test connectors using mock APIs.
If you need sample APIs to test integrations, try this list of 40 Free Testing APIs.

Step 16. Benefits

Building a unified API layer gives your SaaS:

  • Faster integrations
  • Easier maintenance
  • Consistent data
  • Reliable scaling

Adding a new vendor only requires creating a connector, not changing the system.

Summary

A scalable unified API layer simplifies how your SaaS handles external integrations. It centralizes authentication, data models, and monitoring in one place.

If you haven’t yet, check the overview article What Is a Unified API and How It Simplifies Integration Across Platforms to understand the concept before you start building.

Then follow these steps:

  1. Normalize data
  2. Add connectors
  3. Introduce caching and queues
  4. Scale with a gateway and monitoring

This design will keep your SaaS integration layer fast, simple, and ready to grow.

Leave a Reply