[Proposal] Deprecate `onbuild` tags

[yosifkit]

From our docs description of onbuild:

While the onbuild variant is really useful for "getting off the ground running" (zero to Dockerized in a short period of time), it's not recommended for long-term usage within a project due to the lack of control over when the ONBUILD triggers fire (see also docker/docker#5714, docker/docker#8240, docker/docker#11917).

Users are often wanting customization on the order of the onbuild directives (some examples in this search). Since we recommend them only to get started, I think it would be better to just provide an example Dockerfile in the docs for these images.

The following are the onbuild images:

$ bashbrew list --all --uniq | grep onbuild
clojure:onbuild
clojure:alpine-onbuild
django:python3-onbuild
django:python2-onbuild
erlang:19.0.3-onbuild
erlang:18.3.4.3-onbuild
golang:1.6.3-onbuild
golang:1.7.0-onbuild
iojs:1.8.4-onbuild
iojs:2.5.0-onbuild
iojs:3.3.0-onbuild
jruby:9-onbuild
jruby:1.7-onbuild
maven:3.3.9-jdk-7-onbuild
maven:3.3.9-jdk-7-onbuild-alpine
maven:3.3.9-jdk-8-onbuild
maven:3.3.9-jdk-8-onbuild-alpine
maven:3.3.9-jdk-9-onbuild
mono:3.10.0-onbuild
mono:3.12.1-onbuild
mono:3.8.0-onbuild
mono:4.0.5.1-onbuild
mono:4.2.1.102-onbuild
mono:4.2.2.30-onbuild
mono:4.2.3.4-onbuild
mono:4.2.4.4-onbuild
mono:4.4.0.182-onbuild
mono:4.4.1.0-onbuild
mono:4.4.2.11-onbuild
node:0.10.46-onbuild
node:0.12.15-onbuild
node:4.5.0-onbuild
node:5.12.0-onbuild
node:6.4.0-onbuild
pypy:2-5.3.1-onbuild
pypy:3-5.2.0-alpha1-onbuild
python:2.7.12-onbuild
python:3.3.6-onbuild
python:3.4.5-onbuild
python:3.5.2-onbuild
python:3.6.0a3-onbuild
rails:onbuild
ruby:2.1.10-onbuild
ruby:2.2.5-onbuild
ruby:2.3.1-onbuild
sentry:8.6.0-onbuild
sentry:8.7.0-onbuild

[tianon]

I'm +1, but I think we should also probably poke the maintainers of each of these images to see what their thoughts are as well. 👍

[tianon]

I'm still +1 on this after all this time (probably more strongly than before) -- let's cc some maintainers today to see if we get any strong, well-reasoned dissent. I've only seen the onbuild variants cause confusion (especially around what to do when they aren't sufficient), so I think we should axe them.

[tianon]

$ bashbrew list --all --uniq | grep onbuild | cut -d: -f1 | sort -u
clojure
django
erlang
golang
haxe
iojs
jruby
maven
mono
node
pypy
python
rails
ruby
sentry

[tianon]

• clojure:onbuild, cc @Quantisan @cap10morgan
• erlang:onbuild, cc @c0b
• haxe:onbuild, cc @andyli
• jruby:onbuild, cc @cpuguy83
• maven:onbuild, cc @carlossg
• mono:onbuild, cc @directhex
• node:onbuild, cc @chorrell @Starefossen @hmalphettes @jlmitch5 @pesho @retrohacker @mikeal @LaurentGoderre
• sentry:onbuild, cc @mattrobenolt

Please give #2076 (comment) a look and decide whether you have a strong opinion against this. If we don't get good arguments for keeping them (preferably with examples where they've been helpful, but not required), we'll be deprecating onbuild variants.

Concretely, this will mean updating the text in https://github.com/docker-library/docs/blob/20177c318c17c228ae44395feba8fe14f8aa6a3d/.template-helpers/variant-onbuild.md to note that they're deprecated and strongly discouraged, and removing the tags themselves from the "Supported" list of each image over time.

[mattrobenolt]

For Sentry, onbuild is used as the base for https://github.com/getsentry/onpremise

Granted, we could shuffle things around a bit, but I think Sentry's usage of onbuild is a much different story than those of say, python or node, etc. I'm open to accommodating if you want to nuke this concept entirely though. I feel it'd make sense to leave it up to the individual project though.

[cap10morgan]

I am 👍 on getting rid of onbuild variants. They provide so little value for such a short time (of an application's lifecycle) and so easily lead to frustration with their inflexibility that I think they do more harm than good in general.

[chorrell]

I'm 👍 with deprecating onbuild and just providing some example Dockerfiles instead.

[directhex]

Kill it with fire.

[Starefossen]

This is very fine with me 👍🏼 Will solve some common problems!

[tianon]

@mattrobenolt oh, neat! I'm happy to have sentry be an outlier in this case, since you're seeing real value from it (from a functional perspective, that will simply mean we need to leave https://github.com/docker-library/docs/blob/20177c318c17c228ae44395feba8fe14f8aa6a3d/sentry/variant-onbuild.md alone 😄 👍)

As far as general policy goes, I think the consensus seems to be in line with what @yosifkit and I have observed, so if we do go forward with this, we'll simply have a policy that ONBUILD is discouraged and create exceptions for good use cases like sentry's. 👍

[LaurentGoderre]

I also agree and prefer the example Dockerfile

[pesho]

+1 for deprecating -onbuild. A minimal example Dockerfile would better accomplish its purpose, without sacrificing extensibility.

[tracker1]

Kind of sad to see the move to push the -onbuild images out... They've been great, for me in terms of getting a project up/deployed quickly in, for example dokku. I mean, yeah, I can just put all the instructions that would be in -onbuild into the Dockerfile, beyond that, my build is usually a little more complex... that said, the onbuild images have been greatly appreciated.

[carlossg]

I'm 👍 to remove it