Building a resilient payment system is crucial for any organization or business that handles financial transactions. Such a system should be designed to ensure secure, efficient, and uninterrupted payment processing, even in the face of unexpected challenges or attacks. Here are some key principles and strategies to consider when building a resilient payment system.

1. Security First

Prioritize the security of your payment system. Implement industry-standard encryption protocols, secure authentication mechanisms, and comply with relevant data protection regulations (e.g., GDPR, PCI DSS). Regularly conduct security audits and penetration tests to identify and address vulnerabilities. Integrate fraud detection and prevention mechanisms into your payment system. Utilize machine learning algorithms to analyze transaction patterns and identify suspicious activities.

2. Monitoring and Logging

Google's site reliability engineering (SRE) book lists four golden signals a user-facing system should be monitored for latency, traffic, errors, and saturation. Monitoring these metrics can help identify when a system is at risk of going down due to overload. Set up comprehensive monitoring and alerting for your payment system. Continuously track system performance, transaction success rates, and potential anomalies. Proactive monitoring helps identify and address issues before they escalate. Recommended using structured logging in a machine-readable format.

3. Load balancing

Implement load balancing mechanisms to distribute incoming payment requests across multiple servers. Load balancers ensure that no single server is overwhelmed with traffic, improving system performance and availability.

4. Use Idempotency keys

To ensure payment or refund happens exactly once, they recommend using Idempotency keys, which track attempts and provide only a single request is sent to financial partners. https://stripe.com/docs/api/idempotent_requests

5. Be Consistent with Reconciliation

Reconciliation ensures that records are consistent with those of financial partners. Any discrepancies are recorded and automatically remediated where possible.

6. Compliance with Industry Standards

Adhere to relevant payment industry standards and regulations. This includes Payment Card Industry Data Security Standard (PCI DSS) compliance, which ensures the secure handling of credit card information.

7. Regular Testing Regularly test your payment system to identify potential weaknesses and areas for improvement. Stay up-to-date with the latest security patches and updates for all components of the system.

8. Disaster Recovery Plan

Develop a robust disaster recovery plan that outlines the steps to be taken in case of system failures, natural disasters, or cyber-attacks. Regularly test the plan to ensure its effectiveness.

9. Data Redundancy and Replication

Back up and replicate critical payment data in geographically dispersed locations. In case of data loss or corruption, having redundant copies ensures you can quickly restore the system.

10. Incident Retros

Retrospective meetings are held within a week after an incident to understand what happened, correct incorrect assumptions, and prevent the same thing from happening again.