Moderna · Primly Community

Moderna senior / L5 system design interview, what to expect

infra_ines · 4 replies

Just finished my Moderna senior SWE loop (Cambridge, MA, hybrid role) and wanted to leave a data point since there's almost nothing out there about their system design round specifically.

The system design interview was 60 minutes, one interviewer from their digital health platform team. No collab doc, just a verbal discussion with them sketching on a whiteboard. The prompt was roughly: design a system for tracking clinical trial patient data in real time, across multiple sites, with high reliability requirements. I wasn't expected to know anything about mRNA or clinical workflows but they did push on data consistency, audit trails, and how you'd handle partial writes across distributed nodes.

What they actually cared about: Correctness over throughput. This isn't a "scale to 10M req/s" shop. They care deeply about data integrity in regulated environments. Failure handling. The interviewer kept poking at what happens when a site loses connectivity. Graceful degradation, local buffering, reconciliation on reconnect. Compliance surface. They didn't require you to know 21 CFR Part 11 but they wanted you to think out loud about audit logs, immutability, and access control as constraints. Communication. They said multiple times they want engineers who can explain tradeoffs to non-engineers including clinical ops staff.

I drew a pretty standard event-sourced architecture with a CQRS-ish read path. Felt comfortable with it. The interviewer asked why not just use a transactional DB with a simple API. Good question. The conversation ended up being about operational risk tolerance in a biopharma context vs. typical consumer-facing latency.

Difficulty relative to FAANG: noticeably lower ceiling on algorithmic complexity, but the domain framing adds a layer. You need to think through "what breaks in a regulated setting" not just "what breaks at scale."

Level targeted was senior IC, maybe L5 equivalent. Total loop was 5 rounds: phone screen with recruiter, one coding round, system design, behavioral, and a values/culture round with a senior eng.

Happy to answer specifics.

4 replies

infra_ines

The compliance angle is interesting. Do they ask you to talk through any specific regulatory frameworks or is it more that they want to see you thinking about the problem space? I've done healthcare-adjacent infra before and there's a big difference between "we care about audit logs conceptually" and "we need to demonstrate SOC 2 + HIPAA during the design."

remote_swe_42

More conceptual. Nobody used the words HIPAA or 21 CFR in the room. They just kept asking "what if a regulator needed to audit this" and "how would you prove this write actually happened." So it's more about demonstrating the mindset than having certification knowledge.

jp_newgrad

Was it a virtual or in-person onsite? I'm at the phone screen stage for a different Cambridge role and trying to figure out what the rest looks like.

ae_andre

This matches what I've heard from people at biotech companies broadly. The complexity isn't algorithmic, it's sociotechnical. Who uses this system, what goes wrong when they can't, and how would you explain your choices to someone who has never touched a database. That framing matters a lot in regulated industries.