Any plan to support the new ARG command

[djsly]

It would be great if we could provide the maven variables as Docker file build variables.
http://docs.docker.com/engine/reference/builder/#arg

[jgangemi]

if you define the container configuration via the plugin xml, this can already be accomplished. you can also already use maven properties inside a Dockerfile that you have specified as part of the build, but this is very non-portable.

past that, i believe supporting this would require us to parse the Dockerfile to look for these values and re-create a new Dockerfile with everything substituted.

actually...now that i think about this, you could probably accomplish this now provided you were always overriding the value on the command line.

ARG foo=${some.maven.property}

in the above case, the plugin would automatically substitute in the property value and docker would just think a default value was specified and use that. this doesn't work, though, if you wanted to have an actual default value there and only substitute it sometimes.

[djsly]

Our current use case would be around a dockerfile that we manage externally. (not using the auto generated dockerfile feature)

docker build 1.9 provides you with a new docker build flag pass ARG.

so I would see that a new xml attribute could be create

<docker-build-args>
     <docker-build-arg>my_arg=${maven.releaseVersion}</docker-build-arg>
<docker-build-args>

which would translate to the equivalent docker remote API call for

--build-arg my_arg=${maven.releaseVersion}

edit:

from the v1.21 API

POST /build now optionally takes a serialized map of build-time variables.

buildargs – JSON map of string pairs for build-time variables. Users pass these values at build-time. Docker uses the buildargs as the environment context for command(s) run via the Dockerfile’s RUN instruction or for variable expansion in other Dockerfile instructions. This is not meant for passing secret values. Read more about the buildargs instruction

[jgangemi]

hrm - i didn't see that in the api documentation when i looked the first time.

yeah - something like that should definitely be possible then.

[rhuss]

We will consider to support this when we increase the support for external Dockerfiles. Currently these external Dockerfile don't have Maven property substitution (but this is planned for #205)

Luckily we postponed this a bit, because we probably would have chosen the same expression syntax as Docker 1.9 for ARG interpolation (namely ${...}) ;-). So we need sth different for Maven properties if we want to support this as an extension, too. Alternatively we could omit Maven property substitution completely and only use Dockerfile expressions (and feeding in the build-args when building the image).

Docker 1.9 support is planned for 0.14 so it might take a bit, though.

[jgangemi]

my thought here is while we should be accommodating, we shouldn't bend over backwards to support this and the onus should be on the user to do the right thing.

resource filtering in maven is only enabled if you explicitly turn it on, so if someone wants to use the build-args support, they can't run their Dockerfile through maven's resource filtering or they need to use unique property names that won't be known to maven.

they can still turn have a Dockerfile template, we would just recommend they take one approach or the other.

[rhuss]

FYU, my thoughts on the ARG support can be found in #409