Design a Order Processing for Slack
Last updated: September 28, 2025
Quick Overview
Design a distributed order processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Slack
System Design
Software Engineer
Slack
September 28, 2025Software Engineer
Onsite
System Design
Medium
42
12
1,192 solved
Design a distributed order processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Slack asks this during the Onsite to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
Partitioning and sharding strategies
Database selection and data modeling
Failure handling and fault tolerance
Load balancing and horizontal scaling
Consistency models and replication
Monitoring, logging, and alerting
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- What happens if one of your database nodes goes down?
- How would you handle a region-wide outage?
- How would you implement rate limiting to protect the system?
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Requirements
Functional Requirements
- Order Creation: Users can create orders via Slack commands or the Slack app.
- Order Tracking: Users can track the status of their orders in real-time.
- **Not...
Capacity Estimation
- Estimated Daily Active Users: 5 million users.
- Orders per User per Day: Average of 0.2 orders/user, leading to a total of 1 million orders/day.
- Peak QPS Calculation: Assuming ...
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