BuildBarn always resolves symlinks to origin files

[castler]

Our build is relying on the fact that symlinked files are actual symlinks.
It turns out that, using Remote Execution, a file that is symlinked via https://bazel.build/rules/lib/actions#declare_symlink is not an actual symlink, but the file itself.

Apparently there is a Bazel flag (https://bazel.build/reference/command-line-reference#flag--incompatible_remote_symlinks), which is enabled by default, that should ensure exactly this. Following this flag we find bazelbuild/bazel#6631, which describes the needed feature is already implemented by Bazel.

A small repository with a reproduction of the issue can be found here: https://github.com/castler/buildbarn_bazel_symlink_issue_repro

The BuildBarn worker was using the native buildDirectories.

[EdSchouten]

Have you inspected the action through bb_browser? If it shows up as a file there instead of a symlink, then there is little that we can do on the Buildbarn side. Buildbarn tries to literally set up things the way it's provided by Bazel.

[castler]

Thanks for the super quick answer!

I did not check with bb_browser yet, but tried to reproduce with another Remote Execution provider (EngFlow) which did not lead to this case.
Thats why I assumed Bazel is doing its part alright.

Edit: Apparently I did something wrong during my initiale reproduction with our RBE providers. This issue is persistent over different providers, thus indicating (as mentioned farther below) that this is a Bazel issue.

[EdSchouten]

Maybe EngFlow always adds an additional level of symlinks to input roots? Then it would coincidentally work there.

[castler]

ACK.

I will double check the action tomorrow with bb_browser

[castler]

So I was somehow unable to really figure out how to operate bb-browser for actions.
I have no clue where to get the necessary hash and byte size for the actions, can you help me on this?

I used the BEP to finde the hash and byte size for the "symlink artifact". When I visit this in bb-browser
I am presented directly the file not any symlink.

[moroten]

I usually look in the bb-scheduler UI within a minute after the action finishes. Alternatively, I alter the action to exit with a non-zero exit code, to get Bazel to display a link to bb-browser.

[EdSchouten]

Bazel master recently added this flag, which may also be of use:
bazelbuild/bazel#15557
By the looks of it, calling Bazel with that flag will cause it to print the bb-browser URL for every action it runs.

[castler]

Thanks, that helped a lot!

So basically the first thing I see is that apparently the "symlink action" is not executed remotely and indeed the input artifact for the next action is then directly the file. I am trying to figure out now if I have to change something on the config, to make the symlinking also happening remotely.

[EdSchouten]

Awesome! Then let me close this issue on this end, because any changes in this area should most likely be done on the Bazel side. Thanks for reaching out!