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Supporting files are included at skill-relative paths. See UPSTREAM-NOTICE.md for their pinned sources, licenses, hashes, and import changes.

SST v4 for AWS

When to Use

Use this skill when you need sST v4 (Ion) expert for managing AWS resources as code with the Pulumi-backed framework. Use when writing or editing sst.config.ts, building infra/ modules (sst.aws.Function/Bucket/Dynamo/Cron/Service/Router, sst.Secret, sst.Linkable, raw aws.* Pulumi resources), wiring resource links,...

SST v4 (the "Ion" engine) is a Pulumi-backed IaC framework: you describe AWS resources in TypeScript and SST/Pulumi reconciles them into your account. It gives you high-level sst.aws.* components (Function, Bucket, Dynamo, Cron, Service, …) that expand into many underlying resources, plus an escape hatch to any raw Pulumi aws.* resource for the long tail. This skill encodes a production-proven way to author, link, test, deploy, and troubleshoot SST stacks on AWS — distilled from real multi-stack projects that have paid for each lesson with a prod incident.

SST and Pulumi are third-party — verify current syntax with Context7 (resolve-library-id → query-docs for sst or pulumi-aws) when you're unsure about a component's options. Verify AWS-side facts (service limits, model IDs, IAM action names, region availability) with the AWS docs MCP, never from memory. The patterns here are the how; the docs are the what.

When you're invoked

Figure out which mode you're in and jump to the right reference:

Situation	Go to
New project, or adding a resource/module to an existing SST app	Author → references/authoring.md
Wiring one module's output into another (links, SSM, IAM scope)	Author → references/authoring.md § Sharing
Writing tests for infra so changes don't silently break	Test → references/testing.md
Running a deploy, or a deploy just failed	Deploy/Operate → references/deploy-and-troubleshoot.md
Migrating a resource between Pulumi types, renaming a physical name	Deploy/Operate → references/deploy-and-troubleshoot.md § Migrations

Always read the relevant reference before editing — they carry the why behind each rule, which matters more than the rule itself.

Orientation: read the repo before you touch it

SST projects are conventional but not identical. Before editing, build a quick map so your change matches the house style instead of fighting it:

1. sst.config.ts — the app name, home, providers/region, defaultTags, any global $transform (Node runtime pin, bundle fixups), and the order in which run() imports infra/ modules. The import order is the dependency order; respect it.
2. infra/ — one file per domain (storage, functions, api, observability…). This is where resources are declared. Check for an infra/CLAUDE.md — these projects keep IaC-specific rules there, and it's the single most valuable file to read first.
3. infra/tests/ — source-level Vitest assertions that pin resource invariants. If they exist, your change must keep them green and probably needs a new assertion.
4. package.json / .nvmrc — package manager (npm vs pnpm), Node version, and the sst/pulumi versions actually installed.

Run npx sst version to confirm you're on v4/Ion (the $config + .sst/platform/ signature). v2/v3 ("SST Classic", CDK-based) is a different framework — these patterns don't apply there.

The conventions, and which are universal vs tunable

The projects this skill is built from share a deliberate house style. Some of it is universal (true for any SST v4 + AWS project — apply it everywhere); some is project-specific (a sensible default these projects chose — adopt it for consistency, but recognize a project may differ).

Universal — these principles hold for any SST v4 + AWS project:

• Control the Node runtime deliberately, in one place. Don't leave it to whatever the installed SST happens to default to. The idiom is a single global $transform(sst.aws.Function, (args) => { args.runtime ??= "nodejs24.x" }) in run() — ??= is correct here (the transform runs before the component applies its own default, so it fills in only when the user didn't set one). Recent SST already defaults to a current Node runtime, so check the installed default first (Context7); the transform is then version-independence insurance so a future SST downgrade can't silently move your fleet. See references/authoring.md.
• Never interpolate a Pulumi Output<T> into a plain JS template literal. Use $interpolate (or pulumi.interpolate). A bare top-level `${bucket.arn}/*` stringifies the Output to a [Output<T>] placeholder and produces a broken ARN that only fails at deploy time (it type-checks and sst dev runs fine). The fix is $interpolate​`${bucket.arn}/*`. This has caused prod deploy outages. See references/authoring.md § Outputs.
• Migrating a resource between Pulumi types should default to two PRs — Pulumi creates-before-destroys, so for a uniqueness-constrained AWS name (bucket, IAM role, gateway) the old resource still owns it and the create fails with ConflictException. Two sequential deploys (teardown, then recreate) is the conservative default; aliases: / pulumi import / state surgery can bridge identity in some cases but only with a reviewed plan. See references/deploy-and-troubleshoot.md § Migrations.
• Prefer typed sst.aws.* / aws.* resources over the aws.cloudcontrol.Resource escape hatch. CloudControl outputs are stringly-typed and oneOf fields don't patch cleanly. Use it only when no typed resource exists yet, and migrate off it when one ships.

Project-specific defaults — adopt for consistency, but confirm per repo:

• Region ap-northeast-1, home: "aws", and defaultTags carrying Project / Stage / ManagedBy: "sst".
• Stage-gated lifecycle: removal: stage === "prod" ? "retain" : "remove" and protect: stage === "prod" so prod resources survive a stack tear-down and non-prod previews clean up.
• SSM Parameter Store as the out-of-graph contract under a /{app}/{stage}/{domain}/... prefix — for consumers that aren't in the Pulumi graph (CI scripts, sibling apps, operators). For same-app Lambdas, prefer SST link: (it wires a real dependency edge and grants IAM); don't route same-app sharing through SSM. See references/authoring.md § Sharing.
• Lazy await import("./infra/<module>") inside run() so sst dev hot-reload stays light. (For testing, a module export still runs its top-level new sst.aws.* unless it's wrapped in a factory function — see references/testing.md for how to test infra.)
• Source-level Vitest tests on every infra module — a lightweight, house-style regression net asserting on the source text (resource names, index shapes, IAM scopes). It's a deliberate choice, not an SST limit: Pulumi does support runtime mocks (@pulumi/pulumi/runtime) for behavioral graph tests when a module has real logic. Source assertions don't replace a preview-deploy + smoke test. See references/testing.md.
• An observability gate: every new Lambda/queue/schedule gets an alarm and structured logging before merge. Whether you enforce this depends on the project, but it's cheap insurance. See references/deploy-and-troubleshoot.md § Observability.

When you introduce a convention, say which bucket it's in ("this is universal" vs "matching this repo's house style") so the user can override the project-specific ones deliberately.

Working rhythm

1. Orient (above) — map config, modules, tests, tooling.
2. Verify syntax with Context7 / AWS docs MCP if anything is non-obvious. Don't guess at a component's option name.
3. Author the resource/module following references/authoring.md. Match the surrounding file's commenting density and naming — these projects comment the why heavily, and a terse one-liner in a heavily-annotated file reads as a regression.
4. Test — add or update source-level assertions (references/testing.md) and run npx vitest (or the repo's test script). Run npx sst diff and/or tsc --noEmit to catch type and plan errors before deploying.
5. Deploy/operate per references/deploy-and-troubleshoot.md. Confirm the target account with aws sts get-caller-identity before any sst deploy.
6. Clean up any exported state files — they contain account IDs and ARNs and must not linger in /tmp or chat history.

What good looks like

• The change is the smallest diff that satisfies the requirement, in the right infra/ module, wired into run() in dependency order.
• Every Lambda gets the right runtime via the global transform (you didn't hand-set runtime unless intentionally diverging — e.g. a Python function).
• Cross-resource references use link: (in-graph) and/or $interpolate-scoped IAM; outputs other tools consume are published to SSM under the stage prefix.
• New infra has a matching source-level test, and the existing suite stays green.
• You confirmed AWS-side facts via the docs MCP and SST/Pulumi syntax via Context7 rather than relying on recall.
• Anything irreversible (deploy, sst remove, a resource-type migration) was flagged to the user with the account it targets, and migrations were planned as two PRs, not one.

Example

User request:

Use @aws-sst-development for this task: SST v4 (Ion) expert for managing AWS resources as code with the Pulumi-backed framework.

Limitations

• Use this skill only when the task clearly matches its upstream source and local project context.
• Verify commands, generated code, dependencies, credentials, and external service behavior before applying changes.
• Do not treat examples as a substitute for environment-specific tests, security review, or user approval for destructive or costly actions.