How do you connect two software systems that were not built to work together?

First check whether either has an API; if so, a small service between them can translate and move data. If not, exchanging files or, as a last resort, reading a database may work. Whatever the route, decide which system is the source of truth for each piece of data.

By Nazar Kashuba · Reviewed

Businesses accumulate systems that each do one job well and do not talk to each other. Connecting them is usually possible; the question is how robustly.

Options, in rough order of preference

  1. API to API. Both offer interfaces. A small service reads from one, converts, and writes to the other.
  2. Webhooks plus API. One announces events and the other is updated.
  3. File exchange. Exports and imports on a schedule, using CSV or similar, when no interface exists.
  4. Database-level access. Reading the other system’s data directly. Fragile and sometimes forbidden by the vendor; use with care.
  5. Manual with support. Sometimes a tool that makes copying quick and safe is enough.

Decisions that matter more than the technology

  • Source of truth. For each type of data, which system is authoritative? Without this, changes overwrite each other.
  • Direction. One-way or two-way. Two-way sync is much harder.
  • Identity. How do you know a customer in one system is the same as in the other?
  • Errors. What happens when a record is rejected? Who is told?
  • Frequency. Instant, hourly or nightly.

Start with one-way and one data type. Prove it, then extend. And keep logs: the day something looks wrong, they are how you find out why.

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