New version warning output leak in quiet mode

[adrienjt]

Expected behavior

Even when I'm running an outdated version of skaffold, skaffold build -q should only return the templated output, e.g.:

registry/org/image -> registry/org/image:tag

This is especially important when skaffold is run by a CI/CD script.

Actual behavior

Running skaffold v0.12.0, skaffold build -q returns the templated output directly followed by the new version warning, e.g.:

registry/org/image -> registry/org/image:tag
There is a new version (0.13.0) of skaffold available. Download it at https://storage.googleapis.com/skaffold/releases/latest/skaffold-darwin-amd64

[r2d4]

Good catch, you're absolutely right. Sent a fix

[adrienjt]

Thank you for the fix @r2d4 . Actually, I would go a step further and say that, even in "not-quiet" mode, the warning should not appear after the requested templated output. A client may want to see the full log and parse the last line(s) for the requested templated output, e.g., an image tag. IMHO, warnings are safer at the very beginning of stdout... at the risk of being overlooked. What do you think?

[r2d4]

I like the idea @adrienjt, however its implemented a bit differently. We send out a request at the start of the command to check for the update. If that command succeeds before the update check returns, we forget about it so that no extra latency is added. If the update check returns before the command exits, we queue it up and possibly print it at the end.

There is an environment variable SKAFFOLD_UPDATE_CHECK=false that you can set to disable it, which helps a bit.

skaffold/pkg/skaffold/constants/constants.go

Line 53 in 62a4fef

UpdateCheckEnvironmentVariable = "SKAFFOLD_UPDATE_CHECK"

[adrienjt]

Thank you for the explanation @r2d4, you're right, I wouldn't want a non-critical feature (really just informational) to block the critical path. The environment variable is a perfectly fine solution, especially because I don't think I would need it as a human, so I'll just set it in my CI/CD scripts. For other users, it would be nice to document those environment variables, not just in the source code.

Another option would be to display the warning between the Docker output and the templated output, if it's ready by that time, which is more or less the same time as at the end.