Open Stack

Excerpts from Robert Myers's message of 2013-10-29 07:54:59 -0700:
> I'm pulling this conversation out of the gerrit review as I think it needs
> more discussion.
> 
> https://review.openstack.org/#/c/53499/
> 

After reading the comments in that review, it seems to me that you
don't need a client side template for your Heat template.

The only argument for templating is "If I want some things to be
custom I can't have them custom."

You may not realize this, but Heat templates already have basic string
replacement facilities and mappings, which is _all_ you need here.

Use parameters. Pass _EVERYTHING_ into the stacks you're creating as
parameters. Then let admins customize using Heat, not _another_
language.

For instance, somebody brought up wanting to have UserData be
customizable. It is like this now:

UserData:
  Fn::Base64:
    Fn::Join:
    - ''
    - ["#!/bin/bash -v\n",
        "/opt/aws/bin/cfn-init\n",
        "sudo service trove-guest start\n"]

Since you're using yaml, you don't have to se Fn::Join like in json,
so simplify to this first:

UserData:
  Fn::Base64: |
    #!/bin/bash -v
    /opt/aws/bin/cfn-init
    sudo service trove-guest start

Now, the suggestion was that users might want to do a different prep
per service_type. First, we need to make service_type a parameter


Parameters:
  service_type:
    Type: String
    Default: mysql

Now we need to shove it in where needed:

Metadata:
  AWS::CloudFormation::Init:
    config:
      files:
        /etc/guest_info:
          content:
            Fn::Join:
            - ''
            - ["[DEFAULT]\nguest_id=", {Ref: InstanceId},
              "\nservice_type=", {Ref: service_type}, "]"
          mode: '000644'
          owner: root
          group: root

Now, if a user wants to have a different script:

Mappings:
  ServiceToScript:
    mysql:
      script: |
        #!/bin/bash -v
        /opt/aws/bin/cfn-init
        sudo service trove-guest start
    galera:
      script: |
        #!/bin/bash
        /opt/aws/bin/cfn-init
        galera-super-thingy
        sudo service trove-guest start


And then they replace the userdata as such:

UserData:
  Fn::FindInMap:
    - ServiceToScript
    - {Ref: service_type}
    - script

Please can we at least _try_ not to reinvent things!