Custom dockerfiles and build contexts

[simonferquel]

This adds the possibility to specify a custom build context and
Dockerfile for docker components. This makes it easier for adding duffle
compatibility in existing projects.
E.G.: We can now add a simple duffle.json file in the existing
docker/app code base that builds the invocation image from the same
Build context as before, but with a different Dockerfile

duffle.json at the root of my docker-app workspace:

{
    "name": "app",
    "parameters": {
        "k8s_namespace": {
            "defaultValue": "default",
            "type": "string"
        },
        "app_package":{
            "type": "string"
        },
        "settings": {
            "type": "string",
            "destination":{
                "path": "/root/docker-app.settings"
            }
        }
    },
    "credentials": {
        "kubeconfig": {
            "path": "/root/.kube/config"
        }
    },
    "components": {
        "cnab":{
            "name": "cnab",
            "builder" : "docker",
            "configuration":{
                "context": ".",
                "dockerfile": "cnab/Dockerfile",
                "registry": "docker"
            }
        }
    }
}

[radu-matei]

Any particular reason why this is not exposed as the rest of the fields here?

[simonferquel]

it is just that I don't see why it should be exposed... Any particular reason any of these fields should be exposed ? :)

[radu-matei]

At some point in the future we want to vendor out the Duffle build packages for other tools - and those tools might want to to something different with the build context.

[radu-matei]

Could we add this as a constant side by side with the Dockerignore file?

[simonferquel]

we should yes

[radu-matei]

This looks great - there is one thing that might cause some confusion - consider the following component:

[components]
    [components.cnab]
        name = "cnab"
        builder = "docker"
        configuration = { registry = "microsoft", dockerfile = "Dockerfile2" }

The config file (duffle.toml in this case) is at the root of my application - but the dockerfile entry in the config expects a a file relative to the component directory, not relative to the application directory.
This means in a file at the root of the application, I'm putting one property which is relative to the component directory - which is not that intuitive.

[radu-matei]

This looks great - however, there are a couple of small nits, plus the comment about paths that are relative to the application/ component directory, on which I'd like to have a discussion.

Thanks!

[simonferquel]

The rational here is:

• the dockerfile is always relative to the docker build context
• the default docker build context dir is ${COMPONENT_NAME}
• context dirs are relative to the application directory

Does it make sense ? or should we find something less confusing ?

[radu-matei]

Regarding the relative paths - I'm ok with merging this as is, with the mention that we should document this (once we have a doc for building, that is..).

So once the conversations above get resolved, I'll LGTM this and we can merge.

Thanks for the contribution!

[technosophos]

So we're just a few small changes away from being able to merge this, right?

[simonferquel]

rebased, fixed and pushed. PTAL @radu-matei @technosophos