Details
-
New Feature
-
Status: Resolved
-
Major
-
Resolution: Fixed
-
0.9.0
-
None
Description
See the email discussion on dev@brooklyn.apache.org, 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.
