feat: add standalone Alb component for shared load balancers

[ekaya97]

Summary

Add a standalone Alb component that can be shared across multiple Service instances. This allows multiple ECS services to share a single Application Load Balancer with path-based routing.

Fixes #6017 #5510

New API

// Create a shared ALB
const alb = new sst.aws.Alb("SharedAlb", {
  vpc,
  listeners: [{ port: 80, protocol: "http" }],
});

// Attach services with routing rules
new sst.aws.Service("Api", {
  cluster,
  loadBalancer: {
    instance: alb,
    rules: [
      {
        listener: "80/http",
        forward: "3000/http",
        conditions: { path: "/api/*" },
        priority: 100,
      },
    ],
  },
});

Features

• Alb component — standalone ALB with HTTP/HTTPS listeners, SSL/TLS, and DNS integration
• Service integration — loadBalancer.instance option for attaching to external ALBs
• Routing rules — path, header, and query string condition-based routing with explicit priorities
• Reference pattern — Alb.get(name, arn) with lazy listener discovery for cross-stack references
• Linkable — implements Link.Linkable, exposes url for SST linking

Files Changed

File	Changes
platform/src/components/aws/alb.ts	New 705-line ALB component
platform/src/components/aws/service.ts	Union-typed loadBalancer prop, ALB attachment logic
platform/src/components/aws/index.ts	Export Alb
platform/package.json	Added @types/node devDependency
platform/vitest.config.ts	Vitest config (fixes @types/node resolution)
platform/test/components/alb.test.ts	10 unit tests
platform/test/components/service-alb.test.ts	9 integration tests
examples/aws-shared-alb/	HTTP example
examples/aws-shared-alb-domain/	HTTPS with custom domain example

Test plan

• Unit tests pass (35 tests total)
• Deployed aws-shared-alb example to AWS — 7/7 tests pass
• Deployed aws-shared-alb-domain example to AWS — 9/9 tests pass (SSL, HTTP→HTTPS redirect)

HTTP Example Test Results

HTTPS Example Test Results

---

🤖 Generated with Claude Code

[nicholasgubbins]

this is super nice @ekaya97

excited to be able to do router.route(${subdomain}.{domain}, sharedAlb.url)

[ekaya97]

@nicholasgubbins

Thanks!

Check out my other PR #6379 - similar kind of extension concerning WAF in Router.

[teodorrd27]

This is so valuable I've monkey patched my existing sst deployment to deploy in production. It'll be great to see this merged. Thanks for your effort. 🙏