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Designing POS Cash-Session Reconciliation in an ERP

ERP

July 20269 min read

Designing POS Cash-Session Reconciliation in an ERP

How I designed opening float, cash-in/out, expected-vs-counted variance, and an append-only audit trail for a real Indonesian carwash POS.

Idempotency Keys That Stop a POS From Double-Charging

Backend

July 20269 min read

Idempotency Keys That Stop a POS From Double-Charging

How I made carwash POS payment settlement safe against double-taps and network retries using idempotency keys, a Postgres unique constraint, and one guard spec test.

Inventory Truth: A Stock Movement Ledger, Not a Column

Backend

July 20269 min read

Inventory Truth: A Stock Movement Ledger, Not a Column

Why I made SUM of an append-only StockMovement ledger the source of truth in my carwash ERP, and treated Product.stockQty as a cache I rebuild.

Testing NestJS Applications: Unit, Integration, E2E Guide

Backend

July 202611 min read

Testing NestJS Applications: Unit, Integration, E2E Guide

A practical walkthrough of testing NestJS apps at three layers — mocked-provider unit tests, real-database integration tests, and supertest-driven end-to-end tests.

Docker Swarm Load Testing: Why More Replicas Didn't Fix Throughput

DevOps

July 202612 min read

Docker Swarm Load Testing: Why More Replicas Didn't Fix Throughput

During my SRE research at Commsult Indonesia, doubling Docker Swarm replicas cut latency but barely moved throughput, until pg_stat_activity revealed a single locked database row was the real bottleneck.

Building a Custom CPU Autoscaler for Docker Swarm

DevOps

July 202610 min read

Building a Custom CPU Autoscaler for Docker Swarm

Docker Swarm has no Kubernetes-style Horizontal Pod Autoscaler, so during my SGU thesis I built one myself: a Bash daemon with asymmetric streak consensus and a cooldown window.

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