Add support for env. variables as a YAML key

[pritidesai]

We just verified that we do have support for env. variables in #249 and they can be referenced by using ($) dollar notation like $CLOUDANT_USERNAME and $CLOUDANT_PASSWORD in the following example:

package:
    name: openwhisk-data-processing-cloudant
    namespace: _
    dependencies:
        # binding cloudant package named $CLOUDANT_INSTANCE
        $CLOUDANT_INSTANCE:
            location: /whisk.system/cloudant
            inputs:
                username: $CLOUDANT_USERNAME
                password: $CLOUDANT_PASSWORD 

But we do not support env. variables when they are referenced by the YAML keys for example, $CLOUDANT_INSTANCE in the above sample. We do have such use case as part of openwhisk-data-processing-cloudant repo.

@lionelvillard @mrutkows @paulcastro @krook

[lzbj]

@pritidesai , why need to support the $CLOUDANT_INSTANCE key as env, is it related to the dependency management or package binding issue?

[pritidesai]

The key $CLOUDANT_INSTANCE is being used in multiple components including an actions and a trigger, so would like to avoid hard coding same value throughout the manifest file, for example:

package:
    name: data-processing
    namespace: _
    dependencies:
        # binding cloudant package named $CLOUDANT_INSTANCE
        $CLOUDANT_INSTANCE:
            location: /whisk.system/cloudant
            inputs:
                username: $CLOUDANT_USERNAME
                password: $CLOUDANT_PASSWORD
                host: "$CLOUDANT_USERNAME.cloudant.com"
                url: "https://$CLOUDANT_USERNAME:$CLOUDANT_PASSWORD@$CLOUDANT_USERNAME.cloudant.com"
                dbname: $CLOUDANT_DATABASE
    actions:
        # Action named "write-to-cloudant"
        # Creating action that is manually invoked to write to the database
        write-to-cloudant:
            location:  actions/write-to-cloudant.js
            inputs:
                CLOUDANT_USERNAME: $CLOUDANT_USERNAME
                CLOUDANT_PASSWORD: $CLOUDANT_PASSWORD
                CLOUDANT_DATABASE: $CLOUDANT_DATABASE
        # Action named "write-from-cloudant"
        # Creating action to respond to database insertions
        write-from-cloudant:
            location: actions/write-from-cloudant.js
    sequences:
        # Sequence named "write-from-cloudant-sequence"
        # Creating sequence that ties database read to handling action
        write-from-cloudant-sequence:
            actions: $CLOUDANT_INSTANCE/read, write-from-cloudant
    triggers:
        # Trigger named "image-uploaded"
        # Creating trigger to fire events when data is inserted
        image-uploaded:
            source: $CLOUDANT_INSTANCE/changes
            inputs:
                dbname: $CLOUDANT_DATABASE
    rules:
        # Rule named "echo-images"
        # Creating rule that maps database change trigger to sequence
        echo-images:
            trigger: image-uploaded
            action: data-processing/write-from-cloudant-sequence

@krook @paulcastro

[lzbj]

@pritidesai , I think it's good idea, but you know as our yaml parsers are predefined structures, so I don't know if there is a better way to support this flexible environments parsing in yaml, do you know some libraries support this?

[mrutkows]

@pritidesai If we move forward on this, we need another issue to update the specification itself.