Event Sourcing in Go: From Zero to Production

Summary

Key Takeaways Event sourcing provides complete audit trail and time-travel debugging capabilities CQRS separation enables independent scaling of reads and writes Snapshots are essential for performance with large event streams Proper event versioning and migration strategies prevent production disasters Event streaming with Kafka enables real-time projections and system integration Why Event Sourcing? Your database shows current state. But how did it get there? Who changed what? When? Why? -- Traditional: Current state only SELECT balance FROM accounts WHERE id = 123; -- Result: 1000 -- Event sourced: Complete history SELECT * FROM events WHERE aggregate_id = 123; -- Shows every deposit, withdrawal, fee, interest We needed audit trail for financial compliance. Event sourcing gave us that plus time travel, debugging superpowers, and perfect scalability. Core Concepts in 5 Minutes Event sourcing stores state changes as a sequence of events rather than overwriting data. Instead of UPDATE statements that destroy history, we append immutable events that tell the complete story. Traditional systems show what IS. Event sourcing shows what HAPPENED. This distinction transforms debugging, auditing, and analytics. When a bug corrupts data, we can replay events to find exactly when and how it occurred. Events are facts about the past - they cannot be changed or deleted. This immutability provides natural audit logging and enables powerful patterns like temporal queries and retroactive fixes. State becomes a left-fold over events. Current balance isn't stored; it's calculated by replaying all deposits and withdrawals. This sounds slow but with snapshots and projections, it's actually faster than traditional systems for many use cases. // Events capture business intent type AccountOpened struct { AccountID string Currency string } type MoneyDeposited struct { AccountID string Amount decimal.Decimal } // State derived from event history func (a *Account) Apply(event Event) { // R...