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From "Aled Sage (JIRA)" <>
Subject [jira] [Created] (BROOKLYN-286) merge config keys map values, where appropriate
Date Wed, 01 Jun 2016 18:18:59 GMT
Aled Sage created BROOKLYN-286:

             Summary: merge config keys map values, where appropriate
                 Key: BROOKLYN-286
             Project: Brooklyn
          Issue Type: New Feature
    Affects Versions: 0.9.0
            Reporter: Aled Sage

See the email discussion on, subject "[PROPOSAL] merging config keys",
initially kicked off 25/05/2016, 12:12.

Below is a copy of that initial proposal, which has then been further discussed on the mailing

TL;DR: we should merge config when overriding entities/locations, where it's obvious that
such behaviour is desired. For example, where an entity type defines shell.env, then a new
entity extending this type should inherit and add to those values.


_*shell.env in entities*_

When extending an existing entity type in YAML, it is not possible to extend the set of environment
variables. Instead, if the sub-type declares shell.env it will override the inherited values.

For example, consider the catalog items below:

   # Catalog
      - id: machine-with-env
              ENV1: myEnv1

   # Blueprint
   location: ...
   - type: machine-with-env
          ENV2: myEnv2
        launch.command: echo "ENV1=$ENV1, ENV2=$ENV2"

A user might well expect the launch.command to have myEnv1 and myEnv2. However, it does not
get the ENV1 environment variable. This is a real pain when trying to customize stock blueprints.

We propose that the shell.env map should be *merged*.


An entity can be configured with These are passed to the location
when obtaining a new machine. They supplement and override the values configured on the location.
However, for templateOptions the expected/desired behaviour would be to merge the options.

Consider the blueprint below:_*

      minCores: 1
        networks: myNetwork
   - type: org.apache.brooklyn.entity.machine.MachineEntity
          minRam: 2G
            tags: myTag

A user might well expect the VM to be created with the given networks and tags. However, currently
the templateOptions in will override the existing value, rather than
being merged with it.

We propose that the templateOptions map should be *merged*.

Valentin made a start to fix this in

_*_* in sub-entities*_

A similar argument holds for when extending an entity-type in YAML.

If the super-type declares template options, then any additional declared
on the entity sub-type should be *merged* (including merging the templateOptions map contained
within it).

_*files.preinstall, templates.preinstall, etc*_

The same applies for the map config for: files.preinstall, templates.preinstall, files.install,
templates.install, files.runtime and templates.runtime.

We propose that these maps get *merged* with the value defined in the super-type.

_*Overriding default values*_

For default values in the super-type, we propose that this value *does* get overridden, rather
than merged.

For example, in the blueprint below we suggest that the launch-command in the sub-type should
have ENV2 but not ENV_IN_DEFAULT.

      - id: machine-with-env
        version: 1.0.0
          - name: shell.env
              ENV_IN_DEFAULT: myEnvInDefault
      - id: machine-with-env-2
        version: 1.0.0
          type: machine-with-env
              ENV2: myEnv2
            launch.command: echo "ENV_IN_DEFAULT=$ENV_IN_DEFAULT,

(Interestingly, the current behaviour of machine-with-env is that it gets the value for ENV_IN_DEFAULT
but not for ENV2, so sometime strange is going on with re-defining the shell.env config key!)

_*Extending commands: deferred*_

Another scenario is where a super-type declares a value for `install.command`, and the sub-type
wants to augment this by adding additional commands. Currently that is not possible. Instead
the sub-type needs to use pre.install.command and/or post.install.command. But that leads
to the same problem if a super-type also has a value defined for that key.

Svet suggested we could perhaps introduce something like $brooklyn:super().

Unless we can generalise that approach to also solve the merging of `shell.env` etc, then
I suggest we defer the `install.command` use-case. That can be proposed and discussed in a
different thread.

However, if we can solve these problems with clever explicit use of $brooklyn:super(), then
that could provide an elegant solution to all of these problems!

_*Inheritance from parent entities*_

Things are made yet more complicated by the fact we inherit config from parent entities, in
the entity hierarchy.

We propose that this behaviour is also configurable for the config key, but that the defaults
stay as they are. The existing logic is applied to find the config value that applies to the
given entity. That value is then merged with its super-type, as appropriate.

For example, in the blueprint below... machine1 would get ENV1 and ENV2 (i.e. the ENV1 definition
overrides the ENV_IN_APP definition). However, machine2 would get ENV1 and ENV_IN_APP (i.e.
it inherits ENV_IN_APP from the parent, and this is meged with the super-type).

   - type: org.apache.brooklyn.entity.stock.BasicApplication
          ENV_IN_APP: myEnvInApp
      - type: machine-with-env
        id: machine1
            ENV2: myEnv2
      - type: machine-with-env
        id: machine2

The reasoning behind this is to figure out the inheritance/override rules incrementally. We
leave the parent-inheritance as-is, and just focus on the sub-typing inheritance.

Note that there is already a ConfigInheritance defined on ConfigKey for controlling this kind
of inheritance from the parent. The legal values for ConfigInheritance are currently just


Clearly we do not want to implement this piecemeal. We'll add a way to declare that a config
key should be merged with that value from the super-type.

We'll change the Java ConfigKey code to be:

   public interface ConfigKey {
       * @since 0.10.0
      @Nullable ConfigInheritance getParentInheritance();

       * @since 0.10.0
   @Nullable ConfigInheritance getTypeInheritance();

       * @deprecated since 0.10.0; instead use {@link
      @Nullable ConfigInheritance getInheritance();

We'll add to ConfigInheritance support for MERGE. We'll change the name "ALWAYS" to OVERRIDE
(deprecating the old value).

We'll change EntityConfigMap.getConfig to handle this new merge behaviour. And same for locations,
policies and enrichers.

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