feat(aws-lambda): CodeDeploy-managed traffic shifting with smoke tests, canary/linear deployments, and alarm-based rollbacks

[anatolzak]

Summary

Add support for controlled traffic shifting when deploying Lambda functions using AWS CodeDeploy. This gives developers the ability to:

• Validate new versions before any traffic reaches them — run a before-traffic hook that invokes the new version and verifies it works before CodeDeploy shifts traffic
• Gradually shift traffic — canary (send a percentage for a duration, then 100%) or linear (increment by a percentage at regular intervals)
• Automatically roll back on failure — attach CloudWatch alarms that trigger a rollback if error rates or latency spike during the rollout

API

const fn = new sst.aws.Function("Api", {
  handler: "src/api.handler",
  url: true,
  rollout: {
    type: "canary",       // or "linear" or "all-at-once"
    percentage: 10,
    duration: "10 minutes",
    alarms: [errorAlarm.name],
    beforeTraffic: "src/before-traffic.handler",
  },
});

The before-traffic hook uses a new SDK:

import { rollout } from "sst/aws/rollout";

export const handler = rollout.handler(async (event) => {
  const resp = await fetch(Resource.Function.latestUrl);
  await rollout.report(event, resp.ok ? "Succeeded" : "Failed");
});

Features

• Three deployment strategies: all-at-once, canary, linear
• Before/after traffic hooks: validate new versions before shifting traffic, run post-deployment checks after
• CloudWatch alarm integration: automatic rollback if alarms fire during deployment
• SNS notifications: subscribe to deployment lifecycle events (start, success, failure, rollback)
• Conflict handling: configure what happens when a new deploy starts while a rollout is in progress (cancel, rollback, fail)
• Function URL support: url points to the stable alias, latestUrl exposes the latest version for testing
• Works with API Gateway, Router, and other event sources: pass the function directly or use fn.targetArn to route to the stable version
• SST SDK for lifecycle hooks: rollout.handler() for typed events, rollout.report() to report status — no need to use the CodeDeploy SDK directly
• addRollout() for deferred configuration: create the alias upfront, configure the deployment strategy later when you need to reference the function in hook functions