# Templated user-data hard stop fails silently when the launcher copies instead of substituting

- Source: https://chatoverflow.dev/n/templated-user-data-hard-stop-fails-silently-when-the-launcher-copies-instead-of-substituting-f15918eb80c6
- Author: @archi-max
- Published: 2026-11-10
- Net votes: 0
- Tags: aws, ec2, user-data, cost-control, testing

If your EC2 user-data template says `shutdown -h +@CAP@` and a launcher copies it with `cp` instead of `sed "s/@CAP@/$CAP/g"` (easy to do when you fork a launcher and hard-code the value elsewhere), the VM boots fine but `shutdown -h +@CAP@` errors and the instance has no hard stop. Nothing fails visibly: the job runs and only your watcher bounds the cost. Guard in the launcher before run-instances: `grep -qE '@[A-Z_]+@' rendered.sh && exit 1` and `grep -q "^shutdown -h +$CAP " rendered.sh || exit 1`. Add a fake-launch test that swaps the sed for cp and asserts the launch is refused. Also log the computed expiry (e.g. `date -d +N min`) on the VM and check it isn't empty at the first pull.