74 lines
2.3 KiB
Markdown
74 lines
2.3 KiB
Markdown
# ADR-0030: Service Communication Strategy
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## Status
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Accepted
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## Context
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Services need to communicate with each other in a microservices architecture. All communication must go through well-defined interfaces that support network calls.
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## Decision
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Use a **service client-based communication strategy**:
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1. **Service Client Interfaces** (Primary for synchronous calls):
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- Define interfaces in `pkg/services/` for all services
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- All implementations are network-based:
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- `internal/services/grpc/client/` - gRPC clients (primary)
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- `internal/services/http/client/` - HTTP clients (fallback)
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2. **Event Bus** (Primary for asynchronous communication):
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- Distributed via Kafka
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- Preferred for cross-service communication
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- Event-driven architecture for loose coupling
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3. **Shared Infrastructure** (For state):
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- Redis for cache and distributed state
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- PostgreSQL for persistent data
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- Kafka for events
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## Service Client Pattern
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```go
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// Interface in pkg/services/
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type IdentityServiceClient interface {
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GetUser(ctx context.Context, id string) (*User, error)
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CreateUser(ctx context.Context, user *User) (*User, error)
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}
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// gRPC implementation (primary)
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type grpcIdentityClient struct {
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conn *grpc.ClientConn
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client pb.IdentityServiceClient
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}
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// HTTP implementation (fallback)
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type httpIdentityClient struct {
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baseURL string
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httpClient *http.Client
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}
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```
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## Development Mode
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For local development, multiple services can run in the same process, but they still communicate via service clients (gRPC or HTTP) - no direct in-process calls. This ensures the architecture is consistent.
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## Consequences
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### Positive
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- **Unified Interface**: Consistent interface across all services
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- **Easy Testing**: Can mock service clients
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- **Type Safety**: gRPC provides type-safe contracts
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- **Clear Boundaries**: Service boundaries are explicit
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- **Scalability**: Services can be scaled independently
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### Negative
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- **Network Overhead**: All calls go over network
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- **Interface Evolution**: Changes require coordination
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- **Versioning**: Need service versioning strategy
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- **Development Complexity**: More setup required for local development
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## Implementation
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- All services use gRPC clients (primary)
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- HTTP clients as fallback option
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- Service registry for service discovery
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- Circuit breakers and retries for resilience
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