stochastic start failures with possibly erroneous error message?

[Carl Boettiger]

Bug description

Sometimes binder fails to start with the log showing only:

Waiting for build to start...
--build-memory-limit is no longer supported
Check your build engine documentation to set memory limits. Use `docker buildx create` if using the default builder to create a custom builder with appropriate memory limits

Trying again (refreshing the browser page) usually resolves this. However, users (e.g. my students) are often confused by this error message (warning probably, but looks like an error), as nothing in it suggests that the problem might just go away by trying again

How to reproduce

I'm seeing this occasionally on https://github.com/rocker-org/binder, haven't been testing other repos, but only with the central https://mybinder.org/v2/gh/rocker-org/binder/HEAD?urlpath=rstudio launcher.

When I use self-hosted binderhub or fancy profiles, the same repo always builds.

Expected behaviour

Binder starts build

Actual behaviour

Sometimes it works, sometimes it shows the error above.

Your personal set up

So far it always works fine on my personal binderhub, only see this on the mybinder.org launcher. (apologies if there's a different place I should report such bugs!