2 min lesson
System-design mock
Use "System-design mock" to tell the cases apart, then choose a response for each one.
Step 1 of 2
The design round is your home turf as a Core Services EM and the way to waste it is to ramble. Run a timed 45-minute mock on a system you'll actually own and force yourself to lead with opinions the JD explicitly asks for.
Pick exactly one prompt and commit. Switching designs mid-interview reads as indecision and the panel would rather see you go deep than tour three shallow sketches.
OAuth/OIDCOpenID Connect. The modern single sign-on standard, built as an identity layer on top of OAuth 2.0. Where SAML is XML and enterprise-legacy, OIDC is JSON and what newer tools implement first. Press Enter for the full definition. login, token issuance, refresh.
Session vs token, rotation, revocation.
RBACRole-Based Access Control. Granting permissions by role rather than configuring each person individually. Press Enter for the full definition. and enterprise SSOSingle Sign-On. One company login (usually via SAML or OIDC) instead of a separate password per tool. Press Enter for the full definition./SAMLSecurity Assertion Markup Language. The XML-era enterprise standard that powers single sign-on: your identity provider vouches for you to each app. Older than OIDC but still what many enterprise tools speak. Press Enter for the full definition. at the edges.
At-least-once delivery with retries.
DLQ, idempotency, signing, ordering.
Fan-out and throughput at 1M+ DAU scale.
Long-running LLM workflows, streaming.
Queueing, backpressure under bursty load.
State, cost and latency trade-offs.
Interactive diagram. Step through it with the Next and Previous controls below, or Tab to a region to read its detail.
The semantics+SLO step is the gate - skip it and the rest reads as junior altitude.
Learn more
Advanced table
What you must state explicitly
What you must state explicitlyThe non-negotiables
- Dimension
- Delivery semantics
- Weak (vague)
- “We'll retry failed deliveries.”
- Strong (the bar)
- At-least-once with idempotency keys; consumers dedupe; exactly-once is a consumer-side illusion, not a transport guarantee.
- Dimension
- Reliability target
- Weak (vague)
- “It should be highly available.”
- Strong (the bar)
- 99.9% delivery within 60s; error budget spent triggers a freeze; DLQ alert at >0.1% over 5 min.
- Dimension
- Service contract
- Weak (vague)
- “The API sends events.”
- Strong (the bar)
- Versioned event schema, signed payloads, documented retry/timeout behavior, backward-compatible additions only.
- Dimension
- Scale awareness
- Weak (vague)
- “It'll handle the load.”
- Strong (the bar)
- Names the hot path, the sharding key, the cache layer and where the database becomes the bottleneck first.
| Dimension | Weak (vague) | Strong (the bar) |
|---|---|---|
| Delivery semantics | “We'll retry failed deliveries.” | At-least-once with idempotency keys; consumers dedupe; exactly-once is a consumer-side illusion, not a transport guarantee. |
| Reliability target | “It should be highly available.” | 99.9% delivery within 60s; error budget spent triggers a freeze; DLQ alert at >0.1% over 5 min. |
| Service contract | “The API sends events.” | Versioned event schema, signed payloads, documented retry/timeout behavior, backward-compatible additions only. |
| Scale awareness | “It'll handle the load.” | Names the hot path, the sharding key, the cache layer and where the database becomes the bottleneck first. |
Score your recording: if you only landed the left column, you designed at junior altitude.