One customer, kept in step across three systems

The registry already holds 36 customers from day 1, each with a billing number, a primary address and some user addresses. On day 2, 11 records arrive from the three systems. Each one climbs down the ladder and stops at the first rung that finds anyone. One customer found is a match. Two found goes to a person. Nothing found makes a new customer. A name is shown to help people, but the ladder never matches on a name.

The ladder, top rung first

1. Already linked (certain). The record’s own id is already linked to a customer, by an earlier match or a person’s decision.
2. Billing number (certain). The record carries a billing number the registry holds.
3. Primary address (high). The address is exactly one customer’s primary address.
4. User address (high). The address is exactly one customer’s user address.
5. Only customer on the domain (medium). Exactly one customer uses the address’s domain. Free-mail domains never count.

Free-mail domains here: inbox.test. Many unrelated companies use them.

Not run yet. Every record is waiting.

Review queue

Nothing is waiting for a person.

Every change to the registry writes an event to an outbox in the same step as the change, so a change is never saved without its event or sent without being saved. A worker then sends the events to the help desk.

• Each pass claims up to 3 events that are due, skipping any another worker holds, and lets go of the claim before calling the help desk.
• A claim held for 3 minutes by a worker that stopped is taken back.
• The pretend help desk fails every third call. A failed event is tried again after 1, 2 and then 4 minutes, and after 4 failed tries it stops and raises an alert.

Try: run a pass to see the third call fail and wait a minute; run two more to see the stopped worker’s claim taken back; then take the help desk down and keep running passes to see the waits grow until an alert.

Events

• E-1, Claimed

  Beacon: update its seats in the help desk.

  Claimed by worker 2 at minute 0. That worker then stopped.

• E-2, Waiting

  Cobalt: update its plan in the help desk.

  Waiting to be sent.

• E-3, Waiting

  Falcon: update its contact in the help desk.

  Waiting to be sent.

• E-4, Waiting

  Granite: update its seats in the help desk.

  Waiting to be sent.

Worker log

Each pass will appear here.

Billing is the source of truth. Each run reads all 37 billing records and works out a fingerprint of the fields it copies. A target is sent only the records whose fingerprint it has not received, and each target keeps its own, so one target failing never holds the other back. A send that fails all its tries is marked failed and raises an alert; it goes again when the record changes or a full sync sends every record. Billing is never written to.

Try: run it, change billing records and run again; let an agent correct a contact and run again; take the website store down, change billing and run; bring it back and run again (the failed sends wait); then run a full sync.

Not run yet. Neither target has received anything.

Sync log

Each run, note and alert will appear here.

What a signed-in customer sees on the website. The server finds the payment provider’s customer for the sign-in and keeps the answer for 4 minutes, so most loads never wait for the provider. Every button that moves money opens the provider’s own hosted page, so card details never touch the site. It is day 30.

Plans in this invented company: Starter $40 a month, Team $180 a month, Academy $600 a month.