Anatomy of one human

2 min readChapter 04 of 34By Bipin Singh

Before building anything, let's look at a whole "human" — one microservice — from head to toe. Every well-built service has the same body parts, whatever its job. Knowing the map lets you check any service for missing organs.

Every microservice has the same body parts. A missing part — no immune system, no heart monitor, no clear skin — is a design flaw waiting to hurt.

The parts, one by one

Body part	Module	Its single responsibility	Chapter
Senses	Input adapters	Receive stimuli from the outside: requests, events, messages, files, timers	Senses
Skin	Contract and validation	Decide what may enter; reject malformed input early	Senses
Brain	Domain logic	Make decisions and apply business rules	Brain
Memory	Data store	Remember things reliably; nobody else reads it directly	Memory
Voice	Output adapters	Answer callers; announce what happened	Voice and hearing
Ears for others	Subscriptions	Listen to announcements from other humans	Voice and hearing
Hands	Integrations	Act on the outside world safely	Hands
Immune system	Security	Keep out what doesn't belong	Immune system
ID card	Service identity	Prove who this human is to the rest of the world	Immune system
Heart, pulse, diary	Observability	Show how the body is doing, record what happened	Heartbeat and health
DNA	Infrastructure as code	Build an identical body every time	CDK is DNA

A healthy human, a checklist

When you design or review a microservice, walk down the body:

Purpose — can you describe its one job in one sentence?
Senses — which inputs does it accept? Are they documented?
Skin — does it validate every input against a schema?
Brain — is the logic separate from the plumbing (handlers, SDK calls)?
Memory — does it own its data, with nobody else reading its database?
Voice — does it publish events when something important happens?
Hands — do outside calls have timeouts, retries and fallbacks?
Immune system — least-privilege permissions, authentication, encryption?
Heart — logs, metrics, traces, alarms?
DNA — is the whole body defined in code and reproducible?

Key idea

A microservice is not "a Lambda function". It's a whole body: inputs, logic, data, outputs, security, health and the code that builds it. The rest of this section looks at each organ in detail.

How the body is laid out in code

services/
  waiter/                      ← one human
    src/
      senses/                  ← Lambda handlers: API, events, queues (thin)
      skin/                    ← input schemas and validation
      brain/                   ← pure business logic (no AWS calls)
      memory/                  ← repository: reads/writes the service's table
      voice/                   ← event publishing
      hands/                   ← clients for other systems
    infra/
      waiter-dna.ts            ← CDK construct: the body's DNA
    test/

Names like senses/ and brain/ are deliberately playful for teaching — in a real codebase you might call them handlers/, domain/, repository/ and adapters/. The structure is what matters.

Written by Bipin Singh

Senior Full-Stack Engineer · AI & AWS. I design and build serverless systems on AWS — and love explaining them simply.

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