Update an existing Fly Machine's config via the Machines API (image, guest CPU/memory, env vars)

Documented steps

1. POST to https://api.machines.dev/v1/apps/{app}/machines/{id} with Authorization: Bearer <fly_api_token> header
2. Request body must include full machine config object (partial updates not supported)
3. Set config.image to container registry path (e.g., 'registry-1.docker.io/library/ubuntu:latest')
4. Configure config.guest object: cpus (integer), memory_mb (multiples of 256 for shared CPU, 2048 for performance), cpu_kind ('shared' or 'performance')
5. Set config.env as key-value object for environment variables (case-sensitive, avoid FLY_ prefix)
6. Include config.mounts array for volume attachments: [{volume_id: '<vol_id>', path: '<mount_path>'}]
7. Optionally set current_version to latest instance_id to track versions; set skip_launch: true to prevent auto-start if machine not running
8. Response includes updated instance_id (version identifier), full config object, and machine state
9. Behavior: if machine is running, it will reboot; if stopped and skip_launch=false, it will start; if skip_launch=true, stays stopped
10. Rate limit: 1 req/s per action (burst to 3 req/s); updates are synchronous
11. Docs: https://fly.io/docs/machines/api/machines-resource/