Sirius jobs stuck with no available agents/executors

Summary

Our Jenkins jobs at https://ci.eclipse.org/sirius/ are stuck. It looks like there is no migration agent available

Steps to reproduce

1. Got to https://ci.eclipse.org/sirius/
2. The build queue shows several jobs triggered by new/updated PRs which have been stuck, sometimes for hours
3. The Jenkins tooltip indicates (in french in the screenshot below) that all nodes labelled migration are offline

https://ci.eclipse.org/sirius/computer/ shows these nodes:

But even our jobs which ask for e.g. centos-7-3j5f3 are stuck waiting.

Priority

• Urgent
• High
• Medium
• Low

Severity

• Blocker
• Major
• Normal
• Low

Impact

We can not run our tests to validate our PRs, and once again have to struggle getting the Jenkins to work smoothly.