operate-ecs-services-safelylisted

## When to use - About to **change** a deployed service: edit an env var / task-def field, scale replicas, deploy, recycle an instance. - A service is **down**: load balancer returns 502/503, a deploy is stuck below desired replicas, tasks cycle on the LB health check. - A **scheduled/cron worker** isn't doing its job (jobs not running, nothing processed). ## The one principle **Changing an env var, the replica count, or the image is a full deploy — it rolling-restarts tasks.** The *value* you set is rarely what breaks; the **restart** is, because each fresh task must pass the load-balancer health check before it receives traffic. So "just flip an env" or "just scale to 1" has the blast radius of a production deploy. Treat it as one. ## Before you change anything (checklist) 1. **Read the LIVE value first — never assume a default.** The current replica count, image tag, the actual deployed env/secret value, the LB health-check path. Diagnosing or changing from an assumed value is how "small" changes become outages. 2. **Will the health check survive a fresh restart?** If the health endpoint **hard-fails or blocks on a flaky / non-critical dependency**, fix that *first*. A health probe that gates the load balancer must depend only on what's truly required to serve traffic (e.g. the database) — never on a best-effort dependency (a third-party API, a push provider). Otherwise any restart during that dependency's blip kills every task at once. 3. **Check capacity and co-tena