✦ Integration
System integration: getting your business software to talk to each other
System integration is the plumbing that moves data between the separate systems your business already runs - CRM, finance, stock, a portal - so nobody re-types it. Done badly it's a tangle of one-off links; done well it's a small number of predictable connections.
Haystak · 11 August 2026 · Updated 11 August 2026 · 8 min read
System integration is the work of connecting two or more pieces of software so that data created in one place appears, correctly and on time, in another. That might be a new order in your e-commerce site appearing in your finance system, or a customer's address update in your CRM reaching your delivery software without anyone copying and pasting.
Most businesses arrive at this problem gradually. They buy a CRM, then an accounting package, then a stock system, then a portal - each one good on its own, none of them aware the others exist. System integration is how you make the set behave like one system rather than four.
Point-to-point tangle vs a hub
The first integration is easy: connect system A to system B directly. The second is still fine. By the fifth system, you have direct links between most pairs of them, and each new system means several new connections rather than one.
That point-to-point pattern is why integration projects that started cheap end up expensive to touch. Nobody wants to change the CRM's customer record because four other links quietly depend on its exact shape.
| Approach | How it works | Where it goes wrong |
|---|---|---|
| Point-to-point | Each system talks directly to each other system it needs | Connections multiply; one field change breaks several links at once |
| Integration hub / middleware | Each system talks to one central layer, which routes and translates | Costs more to set up; needs someone to own it |
| Shared database | Systems read and write the same data store directly | Fragile, and most modern SaaS products won't allow it anyway |
A hub - sometimes a proper integration platform, sometimes a small custom service we build for exactly this purpose - means each system only has to know how to talk to the hub. Adding a sixth system is one new connection, not five.
Every field needs a source of truth
The question that derails most integration projects is deceptively simple: when the same piece of information exists in two systems, which one is right? Customer address, product price, stock level - pick a system as the single owner for each, and make every other system a reader of that value, not an independent editor.
- One writer per field. If both the CRM and the finance system can edit a customer's payment terms, they will eventually disagree.
- Everyone else reads. Other systems display the value or use it, but changes flow back through the owning system.
- Write it down. A one-page table of field, owning system, and who is allowed to change it settles most arguments before they start.
Sync vs event-driven integration
There are two broad ways to move data between systems, and the choice affects how quickly problems show up and how expensive they are to fix.
- 01Scheduled sync. Every hour, or overnight, a job copies changes across. Simple to build and reason about, but there's a window where the two systems disagree, which matters for stock or pricing.
- 02Event-driven. The source system announces a change the moment it happens (an order placed, a status updated) and the other system reacts immediately, typically via a webhook. Near real-time, but needs more care around retries and ordering.
Most businesses don't need everything in real time. Stock counts and order confirmations usually do; a marketing mailing list update usually doesn't. Matching the method to how much the delay actually costs you keeps the project proportionate.
Error handling and reconciliation
The part of system integration that gets skipped under time pressure is what happens when a transfer fails. A network blip, a system down for maintenance, a record that doesn't validate on the other end - all of these happen regularly, and a good integration expects them rather than being surprised by them.
- Retries with backoff, so a temporary failure doesn't need a human to notice and re-run it.
- A dead-letter queue or error log that someone actually checks, not one that silently fills up.
- Reconciliation reports - a scheduled check that counts and compares totals between systems, catching drift before a customer does.
- Idempotency, so replaying a failed message twice doesn't create a duplicate order or invoice.
What breaks in practice
In our experience, the same handful of things cause most of the pain after go-live, and none of them are exotic.
| What breaks | Usual cause |
|---|---|
| Duplicate customers or orders | No agreed matching key between systems, or retries without idempotency |
| Prices or stock out of step | Sync interval too slow for how fast the value actually changes |
| Integration silently stops working | No monitoring - a vendor changed their API and nobody was watching |
| Fields quietly go blank | A field mapping missed during a vendor's own product update |
Most of these are cheap to prevent and expensive to unpick after the fact, which is why we build monitoring and reconciliation into integration work as standard rather than as an optional extra.
Buying vs building the integration layer
Off-the-shelf integration platforms (iPaaS tools) are a genuinely good answer when you're connecting mainstream SaaS products with well-documented, well-used APIs - they save you building plumbing that already exists. Custom integration earns its keep when a system has no usable API, when the volume or reliability requirements are unusual, or when the logic connecting the systems is itself a piece of business rules rather than a straight data copy.
A short discovery - mapping every system, every field, and who owns it - tells you which situation you're in before anyone commits to a build. If you're weighing that up, our pricing page has a sense of what different scopes of integration project typically involve, or you can talk it through directly.
✦ Where this fits
More on this from us: our system integration services.