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• Payment service and balance ledgerA fintech product lets users pay from a wallet balance. Today a monolith updates a `balances` table in PostgreSQL directly. The mobile app retries requests on poor networks and users are sometimes charged twice. There are a few hundred thousand operations a day, and peak hours carry roughly 5 times the average load. The team wants to move payments into a separate service.
• Notification platformSeveral internal services (orders, payments, marketing) send email, SMS and push notifications. Each service calls the providers directly. When a provider slows down, the order service's response time grows too, some notifications go out twice, and during a marketing campaign critical notifications (such as password resets) are delayed.
• Modernising a legacy platformA bank's internal lending application has run for 12 years: one large Java application, one Oracle database, nightly batch jobs. Releases happen once a month after two weeks of manual testing. The business wants a new online lending product within 6 months. Management proposes to 'rewrite everything as microservices'.