Changes proposed by this PR

This patch adds a new -b/--background option to fly execute. This option tells fly to create the build, and exit just before watching the logs. It also means that outputs can't be retrieved. Instead, the build ID is printed, and logs can then be followed with fly watch.

• added feature with acceptance test
• updated documentation
• left trail in contributors

Rationale

I self-host Gitea and Drone. The application I'm making also needs some worker pool to spawn short-lived processes, and I thought it would be cool to only have one generic job framework to do both. But Drone is not flexible enough for that; besides it has been bought and shut down. I don't want to use frameworks that would lock me in K8S.

So, let's give Concourse a try! CICD works fine, however my jobs are triggered out of nowhere so I can't rely on resource checks to launch them. Although... maybe a custom resource type listing pending jobs with version: every could have somewhat worked, but can't be parallelized... Anyway, I feel spawning one-off tasks fits more to the idea.

I've seen on some pages that ATC's REST API is private, and on some other pages it's somewhat private only because it hasn't been documented yet. Well, my app will communicate through the API for sure, regardless of its privacy! I can't rely on spawning a process and waiting for it, my app can be restarted anytime, and jobs should not depend of that. So I prefer to independently spawn a job, and retrieve its logs.

I thought this workflow could be useful to CLI users too. Build ID is printed so that spawner process can use it (works with Bash and PowerShell).

Note that I don't need to fetch outputs back (yet), but CLI users could benefit from the complete split workflow: fly execute --background + fly watch + to-be-done fly outputs.

Notes to reviewer

I don't master flyIn. It would have been better to test afterwards that fly watch <buildID> would have yield the same outputs as the preceding test, but then test times out. Maybe it's expected that watch keeps running if it's spawned while the build is running too, but I vaguely recall that it exits as soon as the build is completed.

Besides I'm new to Go, so I tried to fit in the code style, but have no idea how idiomatic it is.

Alternative name could have been -d/--daemon (like docker run does), but it implies the process is long-lasting, while it shouldn't.

Release Note

• fly execute gets new -b/--background option to create builds without watching them.