fix(self-improving-mastra): bind app to 0.0.0.0 so Fargate health check passes

[defangdevs]

Problem

Deploying the self-improving-mastra sample to AWS fails: the app service's container health check never passes, ECS kills and replaces the task in a loop, and defang up exits non-zero with:

deployment failed for service "app": TASK_DEACTIVATING Task failed container health checks

The app logs ✓ Ready and even the ALB target reports healthy — but the ECS container health check (curl -f http://localhost:3000/api/health, run inside the task) never connects.

Root cause

Next.js standalone (output: "standalone" → node server.js) binds its HTTP server to process.env.HOSTNAME. The Dockerfile sets ENV HOSTNAME=0.0.0.0 to bind all interfaces — but on Fargate the container runtime injects its own HOSTNAME (the task's private-DNS hostname, e.g. ip-10-0-97-61.us-west-2.compute.internal), and that runtime value overrides the image ENV. So Next binds only to the task's ENI IP:

• ALB health check → hits the ENI IP → healthy ✅
• ECS container health check → curl localhost → nothing on loopback → fails ❌ → task UNHEALTHY → deploy fails

The startup banner in the failing logs confirms it: - Local: http://ip-10-0-97-61.us-west-2.compute.internal:3000 (a real 0.0.0.0 bind prints http://localhost:3000).

This is Next-standalone-specific — it's the only Next.js sample in the repo using standalone output. The others use next start, which binds 0.0.0.0 regardless of HOSTNAME and is unaffected. The dev service passes the identical check because it fronts Next with Caddy, which binds all interfaces.

Fix

CMD ["sh", "-c", "HOSTNAME=0.0.0.0 exec node server.js"]

Force HOSTNAME=0.0.0.0 at launch so the runtime-injected value can't win, and exec so node replaces the shell — staying PID 1 and receiving ECS's SIGTERM directly for graceful shutdown (no signal-swallowing shell wrapper).

Verification

Reproduced and fixed against the exact failing ECR image:

Condition	Bind	curl localhost:3000/api/health
HOSTNAME=0.0.0.0 (intended)	0.0.0.0:3000	{"ok":true}
HOSTNAME=ip-10-0-… (Fargate)	ENI IP only	connection refused
This fix	0.0.0.0:3000	{"ok":true}

Also confirmed node is PID 1 under the fix and exits 0 promptly on SIGTERM.

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