Design a scheduled payment system that lets users schedule a future-dated payment and cancel a pending payment before execution. Specify REST/gRPC APIs to schedule, query status, and cancel; the data model and indexing; how jobs are scheduled and executed (e.g., scheduler, message queue, worker fleet); idempotency and deduplication; ordering and time accuracy (time zones, daylight saving, clock drift); failure handling with retries, backoff, and dead-letter queues; consistency and transactional guarantees with the payment gateway; security and compliance (PCI, encryption, PII); scaling, partitioning, and high availability; monitoring, auditing, and alerting; disaster recovery; and SLAs and capacity estimates.

This question evaluates proficiency in designing a reliable, scalable scheduled payment service, testing competencies in distributed systems, API design, scheduling and execution workflows, idempotency and deduplication, time semantics, transactional consistency, security and compliance, and operational monitoring.

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This is a hard difficulty System Design question, commonly asked during Onsite rounds at Roblox.

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Design a scheduled payment system | Roblox Interview Question

System Design: Scheduled Payment Service

Context

You are designing a backend service that allows end users to:

Schedule a payment for a future date/time.
Query the status of any scheduled payment.
Cancel a payment that has not yet executed.

Assume payments are processed through an external payment gateway, and the system must work reliably at scale across multiple regions.

Requirements

Design the system and cover the following areas:

APIs

Specify REST and/or gRPC APIs for:
- Schedule a payment
- Query payment status
- Cancel a pending payment
Include request/response schema, idempotency, and error handling.

Data Model and Indexing

Propose tables/collections and key fields.
Show indexes required for scheduling queries, user lookups, and idempotency.

Scheduling and Execution

Describe how jobs are scheduled and executed (e.g., scheduler, message queue, worker fleet).
Explain the flow from “scheduled” to “executed”, including the role of delay queues and worker coordination.

Idempotency and Deduplication

Prevent duplicate creation of the same scheduled payment.
Ensure exactly-once semantics for payment submission to the gateway.

Time Semantics

Ordering and time accuracy requirements.
Time zones, daylight saving transitions, and clock drift handling.

Failure Handling

Retries with exponential backoff and jitter.
Dead-letter queues and operational procedures.

Consistency and Transactions

Guarantees when interacting with the payment gateway.
State transitions and transactional boundaries.

Security and Compliance

PCI considerations, encryption, and PII handling.
AuthN/Z for APIs and secrets management.

Scale, Partitioning, and High Availability

Sharding/partitioning strategy and horizontal scaling of components.
Leader election, regional failover, and quorum concerns.

Monitoring, Auditing, and Alerting

Metrics, logs, traces; audit trail design; alerting thresholds.

Disaster Recovery

Backups, RPO/RTO targets, and regional recovery strategy.

SLAs and Capacity Estimates

Availability, latency, accuracy SLAs.
Back-of-envelope capacity and cost drivers.

System Design: Scheduled Payment Service

Context

You are designing a backend service that allows end users to:

Schedule a payment for a future date/time.
Query the status of any scheduled payment.
Cancel a payment that has not yet executed.

Assume payments are processed through an external payment gateway, and the system must work reliably at scale across multiple regions.

Requirements

Design the system and cover the following areas:

APIs

Specify REST and/or gRPC APIs for:
- Schedule a payment
- Query payment status
- Cancel a pending payment
Include request/response schema, idempotency, and error handling.

Data Model and Indexing

Propose tables/collections and key fields.
Show indexes required for scheduling queries, user lookups, and idempotency.

Scheduling and Execution

Describe how jobs are scheduled and executed (e.g., scheduler, message queue, worker fleet).
Explain the flow from “scheduled” to “executed”, including the role of delay queues and worker coordination.

Idempotency and Deduplication

Prevent duplicate creation of the same scheduled payment.
Ensure exactly-once semantics for payment submission to the gateway.

Time Semantics

Ordering and time accuracy requirements.
Time zones, daylight saving transitions, and clock drift handling.

Failure Handling

Retries with exponential backoff and jitter.
Dead-letter queues and operational procedures.

Consistency and Transactions

Guarantees when interacting with the payment gateway.
State transitions and transactional boundaries.

Security and Compliance

PCI considerations, encryption, and PII handling.
AuthN/Z for APIs and secrets management.

Scale, Partitioning, and High Availability

Sharding/partitioning strategy and horizontal scaling of components.
Leader election, regional failover, and quorum concerns.

Monitoring, Auditing, and Alerting

Metrics, logs, traces; audit trail design; alerting thresholds.

Disaster Recovery

Backups, RPO/RTO targets, and regional recovery strategy.

SLAs and Capacity Estimates

Availability, latency, accuracy SLAs.
Back-of-envelope capacity and cost drivers.

Design a scheduled payment system

Quick Overview

System Design: Scheduled Payment Service

Context

Requirements

Solution

Comments (0)

Design a scheduled payment system

Quick Overview

System Design: Scheduled Payment Service

Context

Requirements

Solution

Comments (0)