ddb-lambda-chain

DynamoDB → Lambda → DynamoDB chain

A Go zip Lambda (the provided.al2 custom runtime) driven by DynamoDB Streams, chaining three DynamoDB events end to end against the gopherstack mock AWS API.

This mirrors the canonical AWS pattern (Serverless DynamoDB + Lambda) — a DynamoDB stream invoking a Lambda — but wires it into a small chain so you can watch one event cascade through three tables.

Flow

put item ─▶ chain-1 ──stream──▶ λ chain-fn ──put──▶ chain-2 ──stream──▶ λ chain-fn ──put──▶ chain-3
   (hop 1)                       (hop 1→2)                                (hop 2→3, terminal)

One PutItem into chain-1 produces 3 DynamoDB events: the seed insert, then two stream-driven Lambda copies. The Lambda decides the next table from the stream ARN that triggered it (chain-1 → chain-2 → chain-3); chain-3 has no successor, so the chain stops.

What it exercises (real plumbing, not isolated mocks)

• DynamoDB Streams with NEW_IMAGE view type
• Lambda event source mappings (stream → function) with batching
• Go zip Lambda on real Docker (provided.al2, bootstrap entrypoint)
• The Lambda calling DynamoDB back through the gopherstack endpoint (AWS_ENDPOINT_URL) — full round trip

Run

docker compose up --build --abort-on-container-exit

Expected tail:

=== Result: contents of each table ===
--- chain-1 ---  [{ id: order-42, hop: 1, from: seed }]
--- chain-2 ---  [{ id: order-42, hop: 2, from: chain-1 }]
--- chain-3 ---  [{ id: order-42, hop: 3, from: chain-2 }]

SUCCESS: event chained chain-1 -> chain-2 -> chain-3 (3 DynamoDB events).

Files

file	purpose
lambda/main.go	Go handler (events.DynamoDBEvent → PutItem next table)
lambda/go.mod	aws-lambda-go + aws-sdk-go-v2 deps
demo.sh	build+zip Lambda, create tables/streams/ESMs, seed, verify
docker-compose.yml	gopherstack (with Docker socket) + go/aws-cli demo runner

Notes

• gopherstack mounts the host Docker socket so it can launch the Lambda container; the demo image installs awscli + zip and builds the Go binary.
• The handler only reacts to INSERT events, so it never loops on its own writes beyond the intended chain.