//0x00—architecture

Architecture

Four patterns that recur across the systems I build — shown as the request or event flow, alongside the code that implements the core decision.

//0x01—Event-Driven Pipeline

Order events publish to Pub/Sub and are consumed asynchronously by a Cloud Run worker — decoupling order-taking from analytics so neither blocks the other.

publish.go

 1 func publishOrderEvent(ctx context.Context, t *pubsub.Topic, o Order) error {
 2     data, _ := json.Marshal(o)
 3     result := t.Publish(ctx, &pubsub.Message{Data: data})
 4     _, err := result.Get(ctx) // confirms publish, not processing
 5     return err
 6 }

//0x02—Multi-Tenant SaaS

Tenant identity resolves from JWT claims before a handler runs. PostgreSQL's search_path scopes every query to that tenant's schema — no per-query tenant_id checks required.

middleware.go

 1 func TenantMiddleware(next http.Handler) http.Handler {
 2     return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 3         claims := claimsFromContext(r.Context())
 4         ctx := withTenantSchema(r.Context(), claims.TenantSchema)
 5         next.ServeHTTP(w, r.WithContext(ctx))
 6     })
 7 }

//0x03—M-Pesa Payment Flow

An idempotency key is generated before the Daraja STK push. The webhook callback is signature-verified, then applied as an atomic upsert — retries and duplicates settle to one payment.

upsert.sql

 1 INSERT INTO payments (idempotency_key, order_id, status, amount)
 2 VALUES ($1, $2, 'completed', $3)
 3 ON CONFLICT (idempotency_key) DO NOTHING
 4 RETURNING id;
 5 -- no row returned => already processed, log and exit

//0x04—Real-Time WebSockets

Kitchen order updates publish to a branch-scoped Redis channel. A WebSocket layer subscribed to that channel fans the update out to every connected display in under 200ms.

kds_hub.go

 1 func (h *Hub) HandleOrderEvent(branchID string, payload []byte) {
 2     channel := "branch:" + branchID + ":orders"
 3     h.redis.Publish(ctx, channel, payload)
 4 }
 5 
 6 // subscriber fans out to all websocket clients on this branch