Scheduled jobs

You’ll build a classic background job: every morning, remind customers about invoices that are due, and make it robust: it never double-sends, a missed night just runs later, it’s easy to test, and you hear about failures. You’ll use: schedules, flows, mail, alarms.

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The pattern: a sweep, not a timer per item

Don’t create one delayed job per invoice. Run a short schedule that finds whatever is due now, handles it, and marks it. A missed run just means the next run finds a bit more; nothing is lost if a server restarts.

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1. The table

invoices with: customer_email, amount, due_at (datetime), status (open, paid), and reminded_at (datetime, empty by default). Add an index on (status, due_at) so the sweep is fast as the table grows (Indexes).

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2. The template

Mail → Templates: invoice-due from the Invoice design, values invoice.number, invoice.amount, invoice.due_at, pay_url. Publish it.

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3. The flow

Flows → New flow invoice-reminders, with a Manual run trigger (the schedule starts it):

1. SQL query, node id due: find what’s due and not reminded. Using SQL lets you compare dates:
   SELECT id, number, customer_email, amount, due_at
   FROM invoices
   WHERE status = 'open' AND reminded_at IS NULL AND due_at <= $1
   ORDER BY due_at
   LIMIT 200
   
   with params ["{{ input.scheduled_at }}"].
2. For each over {{ steps.due.output }}. Inside its each branch, the current row is item (and its position index):
   • Send email: To {{ item.customer_email }}, Template invoice-due, Data {"invoice": "{{ item }}", "pay_url": "https://app.example.com/pay/{{ item.id }}"}.
   • Update record: table invoices, id {{ item.id }}, data {"reminded_at": "{{ input.scheduled_at }}"}.
3. A Log block after the loop’s done exit: Reminded {{ steps.due.output | length }} invoices.

A For each handles items one at a time, at most 10,000 per run. See Control flow.

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4. The schedule

Schedules → New schedule: The flow receives { "scheduled_at": "…" }. Using scheduled_at instead of “now” means a late run still uses the time it was meant for.

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5. Test it

1. Create two invoices in development: one due yesterday, one due next week.
2. On the schedule, press Run now.
3. Activity → Flow runs: open the run. The due step should have one row, the loop one iteration.
4. Mail activity: one invoice-due message.
5. Run now again: the due step is now empty, because reminded_at is set. That’s the double-send protection working.

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6. Make failures loud

• An alarm on Failed flow runs above 0 over 60 minutes, emailing your team.
• Activity → Overview flags Schedule invoice-reminders failed on its last run.

If a run fails half-way, the invoices already reminded have reminded_at set and the rest don’t, so re-running is safe: press Run now after fixing the cause.

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Variations