I'm sorry, things got hectic and I bailed on the discussion. I thought I had a handy link to the bug I was thinking of, but I couldn't find a back-link from the issue I'm watching to the one in docker/docker.
Some day I'm sure .dockerignore will be solid, but my confidence level isn't high enough yet (it's getting there) to base my trust on.
My point was that there are other ways that directory structures and what is visible to COPY could have played out where vigilance is less of a problem. It's usually immediately obvious if a file you actually needed is missing from a build, but less obvious that a file that you categorically did NOT want to be there is absent.
Because the system runs in one of those scenarios and dies conspicuously in the other.
I think but am not 100% certain this is the issue I was thinking of, but it seems the most likely, and it was just fixed in 1.10: https://github.com/docker/docker/issues/17911
Some day I'm sure .dockerignore will be solid, but my confidence level isn't high enough yet (it's getting there) to base my trust on.
My point was that there are other ways that directory structures and what is visible to COPY could have played out where vigilance is less of a problem. It's usually immediately obvious if a file you actually needed is missing from a build, but less obvious that a file that you categorically did NOT want to be there is absent.
Because the system runs in one of those scenarios and dies conspicuously in the other.