Mandatory variable syntax in docker-compose.yml is strictly docker 18.04+

[jamiejackson]

Problem description

Docs don't specify that the mandatory variable syntax, ${MYVAR:?} doesn't work for docker stack until docker version 18.04.

Problem location

https://docs.docker.com/compose/compose-file/#variable-substitution

Suggestions for a fix

Add a note.

---

References:

• "invalid interpolation format" when specifying mandatory variables compose#5683

Closing this ticket due to its age, and the impending refactor. If you think this is in error, feel free to reopen. Thanks!

[docker-robott]

Closed issues are locked after 30 days of inactivity.
This helps our team focus on active issues.

If you have found a problem that seems similar to this, please open a new issue.

/lifecycle locked