Skylight Platform Util does not always detect Alpine Linux/musl

[ryansch]

RbConfig::CONFIG['host_os'] seems to reflect the host OS in use when ruby was compiled. If an alpine linux container is being built on an alpine host then we get linux-musl but if an alpine linux container is being built on a libc host then we get either linux or linux-gnu.

This means that the official ruby:2.3.3-alpine container will report linux-gnu back and install the wrong version of libskylight. Here's a copy of my install.log from inside of a ruby:2.3.3-alpine container:

I, [2017-02-16T16:56:53.004002 #13693]  INFO -- : SKYLIGHT_HDR_PATH=/usr/local/bundle/gems/skylight-1.0.1/ext; SKYLIGHT_LIB_PATH=/usr/local/bundle/gems/skylight-1.0.1/lib/skylight/native/x86_64-linux
I, [2017-02-16T16:56:53.004332 #13693]  INFO -- : [SKYLIGHT] fetching native ext; curr-platform=x86_64-linux; requested-arch=x86_64-linux; version=1.0.1-fcb0e55
I, [2017-02-16T16:56:53.004660 #13693]  INFO -- : [SKYLIGHT] attempting to fetch from remote; uri=https://s3.amazonaws.com/skylight-agent-packages/skylight-native/1.0.1-fcb0e55/skylight_x86_64-linux.tar.gz
I, [2017-02-16T16:56:54.649761 #13693]  INFO -- : [SKYLIGHT] successfully downloaded native ext; out=/usr/local/bundle/gems/skylight-1.0.1/ext/skylight_x86_64-linux.tar.gz

This appears to be the root cause behind #59 and #91.

A more reliable way to detect alpine might be to inspect the contents of /etc/os-release or /etc/alpine-release.

[wagenet]

Huh, that's quite odd and seems like a bug in Ruby. However, unless we want to wait for a fix there I guess we'll have to work around it.

[wagenet]

@ryansch have you verified that it works if we use the musl version instead?

[ryansch]

@wagenet I'll fork and do that now.

[wagenet]

@ryansch thanks!

[wagenet]

FWIW, it seems very odd to me that they're building Ruby against libc when it will be used on a platform without it. I'm not sure how this isn't causing lots of problems elsewhere!

[ryansch]

@wagenet Ruby is being built against musl here but the value of host_os only seems to contain musl when alpine is the actual host os (not to be confused with container os).

[wagenet]

@ryansch hmm... I could have sworn I got this to work when Linux was the host! Definitely something weird going on, but Docker isn't my strong suit :/

[ryansch]

@wagenet I can confirm that rails does start now with the musl version of libskylight installed.

Hack: master...outstand:hardcode-musl

[wagenet]

@ryansch thanks for checking this! I'll try to get a proper fix in place soon.

[ryansch]

@wagenet Do you need a small container to test with?

[wagenet]

Looks like RbConfig::CONFIG['arch'] should be safer. Verifying the value on other platforms.

[ryansch]

@wagenet Doesn't look reliable here.

Edit: I don't see the string 'musl' anywhere inside of RbConfig::CONFIG.

[ryansch]

@wagenet Have a look at the output of ldd --version.

ruby:2.3.3-alpine

ruby:2.3.3

[wagenet]

Ah, I was building Ruby as part of the RUN in my Dockerfile. Looks like on the official Ruby Alpine images there is no mention of musl in all of RbConfig 😞 .

[ryansch]

Exactly. Comparing the Dockerfile vs the APKBUILD didn't show anything obvious.

[wagenet]

I'm thinking of doing this:

      OS = case os = RbConfig::CONFIG['host_os'].downcase
      when /linux/
        if ENV['SKYLIGHT_MUSL'] || `ldd --version 2>&1` =~ /musl/
          "linux-musl"
        else
          "linux"
        end

[wagenet]

I don't love it, but I'm not sure of a better way to handle this.

[ryansch]

@wagenet I think that's the best solution right now.

[wagenet]

Should be fixed in 138bb9a

[wagenet]

@ryansch thanks again for your help here!

[ryansch]

@wagenet And thanks for yours!