Aled Sage created BROOKLYN-286:
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Summary: merge config keys map values, where appropriate
Key: BROOKLYN-286
URL: https://issues.apache.org/jira/browse/BROOKLYN-286
Project: Brooklyn
Issue Type: New Feature
Affects Versions: 0.9.0
Reporter: Aled Sage
See the email discussion on [email protected], 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 list.
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.
_*REQUIREMENTS*_
_*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
brooklyn.catalog:
items:
- id: machine-with-env
item:
type:
org.apache.brooklyn.entity.software.base.VanillaSoftwareProcess
brooklyn.config:
shell.env:
ENV1: myEnv1
# Blueprint
location: ...
services:
- type: machine-with-env
brooklyn.config:
shell.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*.
_*provisioning.properties*_
An entity can be configured with provisioning.properties. 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:_*
*_
location:
minCores: 1
templateOptions:
networks: myNetwork
services:
- type: org.apache.brooklyn.entity.machine.MachineEntity
brooklyn.config:
provisioning.properties:
minRam: 2G
templateOptions:
tags: myTag
A user might well expect the VM to be created with the given networks and tags.
However, currently the templateOptions in provisoining.properties 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
https://github.com/apache/brooklyn-server/pull/151.
_*_*provisioning.properties 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
provisioning.properties 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.
brooklyn.catalog:
items:
- id: machine-with-env
version: 1.0.0
item:
type:
org.apache.brooklyn.entity.software.base.VanillaSoftwareProcess
brooklyn.parameters:
- name: shell.env
default:
ENV_IN_DEFAULT: myEnvInDefault
- id: machine-with-env-2
version: 1.0.0
item:
type: machine-with-env
brooklyn.config:
shell.env:
ENV2: myEnv2
launch.command: echo "ENV_IN_DEFAULT=$ENV_IN_DEFAULT,
ENV2=$ENV2"
(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).
services:
- type: org.apache.brooklyn.entity.stock.BasicApplication
brooklyn.config:
shell.env:
ENV_IN_APP: myEnvInApp
brooklyn.children:
- type: machine-with-env
id: machine1
brooklyn.config:
shell.env:
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 ALWAYS and NONE.
_*IMPLEMENTATION*_
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
#getParentInheritance()}
*/
@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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