1.Tech conference talk
When it fits: Use this when your company paid for the ticket, you are attending a talk that touches a decision your team is about to make, and you will be asked what you learned on Monday.
Retiring a monolith one queue at a time, 2026-11-05
Source: Cascade Platform Summit 2026, Hall C, Portland Speaker(s): Halima Rostova, staff engineer, Ledgerline (payments) Why I'm here: Is an event queue a safer way to split our order service than the API gateway approach we sketched in September? Slides or recording: slides promised on the event site by Nov 12 Related: [[Cascade Platform Summit 2026]], [[Order service split]]
Key points (three, in my words)
- They routed writes through a queue first and moved consumers out one at a time, evidence: 38 consumers extracted over 14 months (slide 9).
- Dual writes were the main source of incidents, evidence: 6 of their 9 sev-2 incidents in year one (slide 15).
- They kept the monolith as the source of truth until each consumer had run in shadow mode for 30 days.
Numbers and quotes to check
- "Shadow mode found more bugs than our test suite did" (slide 17)
- p99 latency on checkout went from 420 ms to 310 ms, source the speaker cited: internal dashboard, not published
What I think
- Shadow mode for 30 days is realistic for us. 14 months is not; we have 6 engineers, they had 40.
- Our order service already emits events for billing, so half the queue exists.
Q&A
- Q: How did you handle ordering guarantees? (attendee from a retailer)
- A: Partition by customer ID, accept out-of-order across customers.
People
- Halima Rostova: asked about their shadow-mode diff tool, follow up via the email on her last slide
- Viktor (SRE at a logistics company, met at lunch): same migration, 4 months in, follow up on LinkedIn
Resources mentioned
- Strangler fig pattern write-up, linked on slide 3
- Their open-source diff tool for comparing shadow outputs
Actions
- Two-page proposal: queue-first split for the order service (@me) @due(2026-11-14)
- Email Halima about the diff tool (@me) @due(2026-11-07)
One-line takeaway
Queue-first works if you budget for shadow mode; the dual-write period is where it hurts.