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In step 02 we drew five flat services. Real architectures have boundaries — a VPC, a cluster, a region. iso-topology has two ways to express them:
  1. .d2 nested syntax — auto-translated to iso group
  2. YAML shape: group — for precise placement
We’ll do the .d2 path first because it’s the same source you wrote in step 02 — just one extra brace.

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Wrap the API tier in a VPC

Rewrite services.d2:
Re-render:
The three services inside vpc { … } now sit on a translucent labeled iso panel. Arrows from outside reference parts via dot-notation: vpc.api, vpc.worker, vpc.db.

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Nesting goes deeper

You can nest any number of levels:
iso-topology emits one translucent substrate per level — outer faded, inner stronger. Connectors reference full dot-paths: cluster.region_a.pod -> cluster.region_b.pod.

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YAML equivalent (manual composition)

When you want control over composition that auto-layout can’t give (styled boards, stairs, hero scenes), switch to the YAML DSL. Same primitive — shape: group — but you still don’t compute coordinates: give the group a layout and it arranges the children and sizes its own substrate around them:
mode: row marches the children along the iso x-axis; gap is in cells (1 cell = the canvas gridStep, default 40 world units). Free-standing parts outside a group are positioned the same declarative way with place::
Hand-written offset: {wx, wy} coordinates still work — but treat them as a fine-tune delta on top of place/layout, not the primary mechanism. Every scene in samples/topology is coordinate-free; the langchain-app sample shows grid containers, place chains and auto-sizing in one file. Full grammar: reference/dsl-yaml.md.

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Next step

→ 04-replicas-annotations.md — auto-replicate parts and add screen-space callouts.