Updated ruby/node images

[shleeable]

run all tests I'm aware of. No regressions found.

Ruby 2.5.1 is a standard release. lots of backport bugfixes. (2018-03-28)
Node 8.12 is a LTS release (2018-09-11)
Alpine is a bonus.

• https://www.ruby-lang.org/en/news/2018/03/28/ruby-2-5-1-released/
• https://nodejs.org/en/blog/release/v8.12.0/

[ladyisatis]

@Gargron Does Ruby 2.5.1 still segfault randomly on Docker? I have reservations about this if the segfault issue has not been fixed. See #6734 and #7257

[shleeable]

@reverite I submitted this PR after a 48 hour testing period with no errors on sidekick for me... but I'll keep an eye open on my docker containers and revert if I notice ANY regression.

I am hoping to get more involved with Mastodon development so I've tried to be careful.

1. I've been running my development Mastodon with ruby 2.5.1 for 4 days.... and I've pushed those changes to my production instance 2 days ago - while that's not a lot of time, as mentioned above, I'll keep my eyes peeled.

2. jemalloc does infact still break on docker with ruby on alpine 3.6 - and as Reduce Sidekiq memory usage 2-4x #7257, I've been planning to build jemalloc into docker because people are using it on non-docker installs, but I need to do additional testing before I PR my branch with that...

https://bugs.ruby-lang.org/issues/13524 states that my issues might be resolved with the move to alpine 3.7

[ladyisatis]

@ashleyhull-versent jemalloc is not compatible with Alpine because jemalloc and musl conflict. I'd say that jemalloc would probably work for debian:stable-slim, but the trade-off would be increased bundle size.

I run Alpine 3.7 on my own instance, and have seen improvements in build times, etc. I think the same would also happen with Alpine 3.8. It's some change in Ruby 2.5 that is segfaulting when running inside Docker, and this does not happen outside of Docker, nor does it happen when running on Ruby 2.4 inside Docker.

[nightpool]

the jemalloc/musl information seems out of date, according to that very link:

With the recent changes to allow interposing malloc, projects that want to use it now can, but it definitely shouldn't be imposed on the vast majority of programs that will only hurt (grow much bigger in memory) from using it.

[shleeable]

This is one of those things... The next stable release 2.5.2 will support alpine 3.8 and sidekick has multiple releases (5.1.3 -> 5.2.2) that could be upgraded as well.

I'm going to wait for everything to fall into place, upgrade and we if still experience the same problems - start to diagnose the issue in more detail.

regarding the malloc stuff, I'm waiting for these blockers to be resolved before I jump down that rabbit hole.. but I'd like to be using jemalloc by default under docker if possible in the future.

Because it took 4 days for this bug to trigger for me on my production instance.. slow and steady.