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Golang / GoLang System Architecture and Testing Interview Questions

How do you decide where to draw service boundaries when decomposing a Go monolith into microservices?

Service decomposition is one of the hardest architectural decisions. Decomposing too aggressively creates a 'distributed monolith' — all the complexity of microservices with none of the benefits. Decomposing too conservatively keeps the monolith's disadvantages.

Decomposition Principles
PrincipleDescriptionGo Implication
Domain-Driven DesignSplit by bounded context — User, Order, Inventory are separate domainsEach service owns its schema; no cross-schema JOINs
Single ResponsibilityEach service does one thing well; change one thing without touching othersOne binary per domain; small team ownership
Data OwnershipService owns its data; others access via API — no shared DB tablesSeparate databases or schemas; eventual consistency via events
DeployabilityCan each service be deployed independently?Separate CI/CD pipelines; semantic versioning of gRPC APIs
Failure IsolationDoes one service's failure propagate?Circuit breakers; timeout on every cross-service call
Strangler FigMigrate gradually — route traffic by feature flagProxy in Go; run old+new in parallel
// Anti-pattern: too-fine decomposition (nanoservices)
// UserNameService, UserEmailService, UserAgeService
// → Every user operation requires 3 network calls
// → Synchronous coupling worse than a monolith

// Better: domain-aligned decomposition
// UserService:   manage user profiles and authentication
// OrderService:  manage order lifecycle and payments
// NotifyService: send emails/SMS/push — consumes events from others

// Strangler Fig pattern in Go
func routeToNewService(cfg *Config) http.Handler {
    legacyHandler := newLegacyHandler()
    newHandler    := newModernHandler()

    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Gradually shift traffic using feature flags
        if cfg.Features.IsEnabled("new-user-service") &&
            strings.HasPrefix(r.URL.Path, "/users/") {
            newHandler.ServeHTTP(w, r)
            return
        }
        legacyHandler.ServeHTTP(w, r)
    })
}

What is the 'distributed monolith' anti-pattern in microservices?
According to the Data Ownership principle, how should one service access another service's data?

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