Maintain preseeded containers running.

It would be awesome if you could have a minimum number of containers running at any given time (each with a run once strategy).

1. Let’s say you set the minimum number of active “run once” containers to 5. Then even though there are no builds queued up the docker plugin ensures that there’s at least 5 “run once” containers actively running.
2. Then a build comes in and takes up one of the “run once” executors. When the build finishes it deletes the docker container. The result is no there are only 4 “run once” containers actively running.
3. The docker-plugin notices there’s only 4 “run once” instances but it should have 5. It then proceeds to provision 1 additional container so that there are 5 ready to go containers.

In my use case, I have one container image ready to build all types of projects. So any pull requests that come in or main builds that are executed make use of the same container image. It takes time to spin up a new container for each build in the queue. Therefore, it would be nice to have a minimum set of active containers but elastically expand that number as more are needed.

This setting should be available in the Images section and configurable per image that’s referenced. Default should be 0 which is what it currently is today.

[samrocketman]

Not everyone’s needs are the same. There’s a startup cost to a Jenkins agent more than creating a container. Not sure where you got your metric but my experience has been different. If you don’t plan to implement this then fine. Please reopen so someone in the community can get to it (maybe even me).

[samrocketman]

That sounds great @ndeloof.