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Entity Configuration

Within a blueprint or catalog item, entities can be configured. The rules for setting this configuration, including when composing and extending existing entities, is described in this section.

Basic Configuration

Within a YAML file, entity configuration should be supplied within a brooklyn.config map. It is also possible to supply configuration at the top-level of the entity. However, that approach is discouraged as it can sometimes be ambiguous (e.g. if the config key is called “name” or “type”), and also it does not work in all contexts such as for an enricher’s configuration.

A simple example is shown below:

services:
- type: org.apache.brooklyn.entity.webapp.tomcat.TomcatServer
  brooklyn.config:
    webapp.enabledProtocols: http
    http.port: 9080
    wars.root: https://search.maven.org/remotecontent?filepath=org/apache/brooklyn/example/brooklyn-example-hello-world-webapp/0.12.0/brooklyn-example-hello-world-webapp-0.12.0.war # BROOKLYN_VERSION

If no config value is supplied, the default for that config key will be used. For example, http.port would default to 8080 if not explicitly supplied.

Some config keys also have a short-form (e.g. httpPort instead of http.port would also work in the YAML example above). However, that approach is discouraged as it does not work in all contexts such as for inheriting configuration from a parent entity.

Configuration in a Catalog Item

When defining an entity in the catalog, it can include configuration values like any other blueprint (i.e. inside the brooklyn.config block).

It can also explicitly declare config keys, using the brooklyn.parameters block. The example below illustrates the principle:

brooklyn.catalog:
  items:
  - id: entity-config-example
    itemType: entity
    name: Entity Config Example
    item:
      type: org.apache.brooklyn.entity.software.base.VanillaSoftwareProcess
      brooklyn.parameters:
      - name: custom.message
        type: string
        description: Message to be displayed
        default: Hello
      brooklyn.config:
        shell.env:
          MESSAGE: $brooklyn:config("custom.message")
        launch.command: |
          echo "My example launch command: $MESSAGE"
        checkRunning.command: |
          echo "My example checkRunning command: $MESSAGE"

Once added to the catalog, it can be used with the simple blueprint below (substituting the location of your choice). Because no configuration has been overridden, this will use the default value for custom.message, and will use the given values for launch.command and checkRunning.command:

location: aws-ec2:us-east-1
name: entity-config-example
services:
- type: entity-config-example

For details of how to write and add catalog items, see Catalog, and for a complete reference on the syntax of brooklyn.parameters see that section of the YAML Reference.

Config Key Constraints

The config keys in the brooklyn.parameters can also have constraints defined, for what values are valid. If more than one constraint is defined, then they must all be satisfied. The constraints can be any of:

  • required: deployment will fail if no value is supplied for this config key.
  • regex: ...: the value will be compared against the given regular expression.
  • A predicate, declared using the DSL $brooklyn:object.

This is illustrated in the example below:

brooklyn.catalog:
  items:
  - id: entity-constraint-example
    itemType: entity
    name: Entity Config Example
    item:
      type: org.apache.brooklyn.entity.stock.BasicEntity
      brooklyn.parameters:
      - name: compulsoryExample
        type: string
        constraints:
        - required
      - name: addressExample
        type: string
        constraints:
        - regex: ^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$
      - name: numberExample
        type: double
        constraints:
        - $brooklyn:object:
            type: org.apache.brooklyn.util.math.MathPredicates
            factoryMethod.name: greaterThan
            factoryMethod.args:
            - 0.0
        - $brooklyn:object:
            type: org.apache.brooklyn.util.math.MathPredicates
            factoryMethod.name: lessThan
            factoryMethod.args:
            - 256.0

An example usage of this toy example, once added to the catalog, is shown below:

name: entity-constraint-example
services:
- type: entity-constraint-example
  brooklyn.config:
    compulsoryExample: foo
    addressExample: 1.1.1.1
    numberExample: 2.0

Inheriting Configuration

Configuration can be inherited from a super-type, and from a parent entity in the runtime management hierarchy. This applies to entities and locations. In a future release, this will be extended to also apply to policies and enrichers.

When a blueprint author defines a config key, they can explicitly specify the rules for inheritance (both for super/sub-types, and for the runtime management hiearchy). This gives great flexibilty, but should be used with care so as not to surprise users of the blueprint.

The default behaviour is outlined below, along with examples and details of how to explilcitly define the desired behaviour.

Normal Configuration Precedence

There are several places that a configuration value can come from. If different values are specified in multiple places, then the order of precedence is as listed below:

  1. Configuration on the entity itself
  2. Inherited configuration from the super-type
  3. Inherited configuration from the runtime type hierarchy
  4. The config key’s default value

Inheriting Configuration from Super-type

When using an entity from the catalog, its configuration values can be overridden. For example, consider the entity-config-example added to the catalog in the section Configuration in a Catalog Item. We can override these values. If not overridden, then the existing values from the super-type will be used:

location: aws-ec2:us-east-1
name: entity-config-override-example
services:
- type: entity-config-example
  brooklyn.config:
    custom.message: Goodbye
    launch.command: |
      echo "Sub-type launch command: $MESSAGE"

In this example, the custom.message overrides the default defined on the config key. The launch.command overrides the original command. The other config (e.g. checkRunning.command) is inherited unchanged.

It will write out: Sub-type launch command: Goodbye.

Inheriting Configuration from a Parent in the Runtime Management Hieararchy

Configuration passed to an entity is inherited by all child entities, unless explicitly overridden.

In the example below, the wars.root config key is inherited by all TomcatServer entities created under the cluster, so they will use that war:

services:
- type: org.apache.brooklyn.entity.group.DynamicCluster
  brooklyn.config:
    wars.root: https://search.maven.org/remotecontent?filepath=org/apache/brooklyn/example/brooklyn-example-hello-world-webapp/0.12.0/brooklyn-example-hello-world-webapp-0.12.0.war # BROOKLYN_VERSION
    dynamiccluster.memberspec:
      $brooklyn:entitySpec:
        type: org.apache.brooklyn.entity.webapp.tomcat.TomcatServer

In the above example, it would be better to have specified the wars.root configuration in the TomcatServer entity spec, rather than at the top level. This would make it clearer for the reader what is actually being configured.

The technique of inherited config can simplify some blueprints, but care should be taken. For more complex (composite) blueprints, this can be difficult to use safely; it relies on knowledge of the internals of the child components. For example, the inherited config may impact multiple sub-components, rather than just the specific entity to be changed. This is particularly true when using complex items from the catalog, and when using common config values (e.g. install.version).

An alternative approach is to declare the expected configuration options at the top level of the catalog item, and then (within the catalog item) explicitly inject those values into the correct sub-components. Users of this catalog item would set only those exposed config options, rather than trying to inject config directly into the nested entities.

DSL Evaluation of Inherited Config

When writing blueprints that rely on inheritance from the runtime management hierarchy, it is important to understand how config keys that use DSL will be evaluated. In particular, when evaluating a DSL expression, it will be done in the context of the entity declaring the config value (rather than on the entity using the config value).

For example, consider the config value $brooklyn:attributeWhenReady("host.name") declared on entity X, and inherited by child entity Y. If entity Y uses this config value, it will get the “host.name” attribute of entity X.

Below is another (contrived!) example of this DSL evaluation. When evaluating refExampleConfig, it retrievies the value of exampleConfig which is the DSL expression, and evaluates this in the context of the parent entity that declares it. Therefore $brooklyn:config("ownConfig") returns the parent’s ownConfig value, and the final result for refExampleConfig is set to “parentValue”:

services:
- type: org.apache.brooklyn.entity.stock.BasicApplication
  brooklyn.config:
    ownConfig: parentValue
    exampleConfig: $brooklyn:config("ownConfig")
  
  brooklyn.children:
  - type: org.apache.brooklyn.entity.stock.BasicEntity
    brooklyn.config:
      ownConfig: childValue
      refExampleConfig: $brooklyn:config("exampleConfig")

However, the web-console also shows other misleading (incorrect!) config values for the child entity. It shows the inherited config value of exampleConfig as “childValue” (because the REST api did not evaluate the DSL in the correct context, when retrieving the value! See https://issues.apache.org/jira/browse/BROOKLYN-455.

Merging Configuration Values

For some configuration values, the most logical behaviour is to merge the configuration value with that in the super-type. This depends on the type and meaning of the config key, and is thus an option when defining the config key.

Currently it is only supported for merging config keys of type Map.

Some common config keys will default to merging the values from the super-type. These config keys
include those below. The value is merged with that of its super-type (but will not be merged with the value on a parent entity):

  • shell.env: a map of environment variables to pass to the runtime shell
  • files.preinstall: a mapping of files, to be copied before install, to destination name relative to installDir
  • templates.preinstall: a mapping of templates, to be filled in and copied before pre-install, to destination name relative to installDir
  • files.install: a mapping of files, to be copied before install, to destination name relative to installDir
  • templates.install: a mapping of templates, to be filled in and copied before install, to destination name relative to installDir
  • files.runtime: a mapping of files, to be copied before customisation, to destination name relative to runDir
  • templates.runtime: a mapping of templates, to be filled in and copied before customisation, to destination name relative to runDir
  • provisioning.properties: custom properties to be passed in when provisioning a new machine

A simple example of merging shell.env is shown below (building on the entity-config-example in the section Configuration in a Catalog Item). The environment variables will include the MESSAGE set in the super-type and the MESSAGE2 set here:

location: aws-ec2:us-east-1
services:
- type: entity-config-example
  brooklyn.config:
    shell.env:
      MESSAGE2: Goodbye
    launch.command: |
      echo "Different example launch command: $MESSAGE and $MESSAGE2"

To explicitly remove a value from the super-type’s map (rather than adding to it), a blank entry can be defined.

Entity provisioning.properties: Overriding and Merging

An entity (which extends SoftwareProcess) can define a map of provisioning.properties. If the entity then provisions a location, it passes this map of properties to the location for obtaining the machine. These properties will override and augment the configuration on the location itself.

When deploying to a jclouds location, one can specify templateOptions (of type map). Rather than overriding, these will be merged with any templateOptions defined on the location.

In the example below, the VM will be provisioned with minimum 2G ram and minimum 2 cores. It will also use the merged template options value of {placementGroup: myPlacementGroup, securityGroupIds: sg-000c3a6a}:

location:
  aws-ec2:us-east-1:
    minRam: 2G
    templateOptions:
      placementGroup: myPlacementGroup
services:
- type: org.apache.brooklyn.entity.machine.MachineEntity
  brooklyn.config:
    provisioning.properties:
      minCores: 2
      templateOptions:
        securityGroupIds: sg-000c3a6a

The merging of templateOptions is shallow (i.e. maps within the templateOptions are not merged). In the example below, the userMetadata value within templateOptions will be overridden by the entity’s value, rather than the maps being merged; the value used when provisioning will be {key2: val2}:

location:
  aws-ec2:us-east-1:
    templateOptions:
      userMetadata:
        key1: val1
services:
- type: org.apache.brooklyn.entity.machine.MachineEntity
  brooklyn.config:
    provisioning.properties:
      userMetadata:
        key2: val2

Re-inherited Versus not Re-inherited

For some configuration values, the most logical behaviour is for an entity to “consume” the config key’s value, and thus not pass it down to children in the runtime type hierarchy. This is called “not re-inherited”.

Some common config keys that will not re-inherited include:

  • install.command (and the pre.install.command and post.install.command)
  • customize.command (and the pre.customize.command and post.customize.command)
  • launch.command (and the ``pre.launch.command and post.launch.command`)
  • checkRunning.command
  • stop.command
  • The similar commands for VanillaWindowsProcess powershell.
  • The file and template install config keys (e.g. files.preinstall, templates.preinstall, etc)

An example is shown below. Here, the “logstash-child” is a sub-type of VanillaSoftwareProcess, and is co-located on the same VM as Tomcat. We don’t want the Tomcat’s configuration, such as install.command, to be inherited by the logstash child. If it was inherited, the logstash-child entity might re-execute the Tomcat’s install command! Instead, the install.command config is “consumed” by the Tomcat instance and is not re-inherited:

services:
- type: org.apache.brooklyn.entity.webapp.tomcat.Tomcat8Server
  brooklyn.config:
    children.startable.mode: background_late
  brooklyn.children:
  - type: logstash-child
    brooklyn.config:
      logstash.elasticsearch.host: $brooklyn:entity("es").attributeWhenReady("urls.http.withBrackets")
...

“Not re-inherited” differs from “never inherited”. The example below illustrates the difference, though this use is discouraged (it is mostly for backwards compatibility). The post.install.command is not consumed by the BasicApplication, so will be inherited by the Tomcat8Server which will consume it. The config value will therefore not be inherited by the logstash-child.

services:
- type: org.apache.brooklyn.entity.stock.BasicApplication
  brooklyn.config:
    post.install.command: echo "My post.install command"
  brooklyn.children:
  - type: org.apache.brooklyn.entity.webapp.tomcat.Tomcat8Server
    brooklyn.config:
      children.startable.mode: background_late
    brooklyn.children:
    - type: logstash-child
      brooklyn.config:
        logstash.elasticsearch.host: $brooklyn:entity("es").attributeWhenReady("urls.http.withBrackets")
...

Never Inherited

For some configuration values, the most logical behaviour is for the value to never be inherited in the runtime management hiearchy.

Some common config keys that will never inherited include:

  • defaultDisplayName: this is the name to use for the entity, if an explicit name is not supplied. This is particularly useful when adding an entity in a catalog item (so if the user does not give a name, it will get a sensible default). It would not be intuitive for all the children of that entity to also get that default name.

  • id: the id of an entity (as supplied in the YAML, to allow references to that entity) is not inherited. It is the id of that specific entity, so must not be shared by all its children.

Inheritance Modes: Deep Dive

The javadoc in the code is useful for anyone who wants to go deep! See org.apache.brooklyn.config.BasicConfigInheritance and org.apache.brooklyn.config.ConfigInheritances in the repo https://github.com/apache/brooklyn-server.

When defining a new config key, the exact semantics for inheritance can be defined. There are separate options to control config inheritance from the super-type, and config inheritance from the parent in the runtime management hierarchy.

The possible modes are:

  • NEVER_INHERITED: indicates that a key’s value should never be inherited (even if defined on an entity that does not know the key). Most usages will prefer NOT_REINHERITED.

  • NOT_REINHERITED: indicates that a config key value (if used) should not be passed down to children / sub-types. Unlike NEVER_INHERITED, these values can be passed down if they are not used by the entity (i.e. if the entity does not expect it). However, when used by a child, it will not be passed down any further. If the inheritor also defines a value the parent’s value is ignored irrespective (as in OVERWRITE; see NOT_REINHERITED_ELSE_DEEP_MERGE if merging is desired).

  • NOT_REINHERITED_ELSE_DEEP_MERGE: as NOT_REINHERITED but in cases where a value is inherited because a parent did not recognize it, if the inheritor also defines a value the two values should be merged.

  • OVERWRITE: indicates that if a key has a value at both an ancestor and a descendant, the descendant and his descendants will prefer the value at the descendant.

  • DEEP_MERGE: indicates that if a key has a value at both an ancestor and a descendant, the descendant and his descendants should attempt to merge the values. If the values are not mergable, behaviour is undefined (and often the descendant’s value will simply overwrite).

Explicit Inheritance Modes

The YAML support for explicitly defining the inheritance mode is still work-in-progress. The options documented below will be enhanced in a future version of AMP, to better support the modes described above.

In a YAML blueprint, within the brooklyn.parameters section for declaring new config keys, one can set the mode for inheritance.type and inheritance.runtime (i.e. for inheritance from the super-type, and inheritance in the runtime management hierarchy). The possible values are:

  • deep_merge: the inherited and the given value should be merged; maps within the map will also be merged
  • always: the inherited value should be used, unless explicitly overridden by the entity
  • none: the value should not be inherited; if there is no explicit value on the entity then the default value will be used

Below is a (contrived!) example of inheriting the example.map config key. When using this entity in a blueprint, the entity’s config will be merged with that defined in the super-type, and the parent entity’s value will never be inherited:

brooklyn.catalog:
  items:
  - id: entity-config-inheritance-example
    version: "1.1.0-SNAPSHOT"
    itemType: entity
    name: Entity Config Inheritance Example
    item:
      type: org.apache.brooklyn.entity.machine.MachineEntity
      brooklyn.parameters:
      - name: example.map
        type: java.util.Map
        inheritance.type: deep_merge
        inheritance.runtime: none
        default:
          MESSAGE_IN_DEFAULT: InDefault
      brooklyn.config:
        example.map:
          MESSAGE: Hello

The blueprints below demonstrate the various permutations for setting configuration for the config example.map. This can be inspected by looking at the entity’s config. The config we see for app1 is the inherited {MESSAGE: "Hello"}; in app2 we define additional configuration, which will be merged to give {MESSAGE: "Hello", MESSAGE_IN_CHILD: "InChild"}; in app3, the config from the parent is not inherited because there is an explicit inheritance.runtime of “none”, so it just has the value {MESSAGE: "Hello"}; in app4 again the parent’s config is ignored, with the super-type and entity’s config being merged to give {MESSAGE: "Hello", MESSAGE_IN_CHILD: "InChild"}.

location: aws-ec2:us-east-1
services:
- type: org.apache.brooklyn.entity.stock.BasicApplication
  name: app1
  brooklyn.children:
  - type: entity-config-inheritance-example

- type: org.apache.brooklyn.entity.stock.BasicApplication
  name: app2
  brooklyn.children:
  - type: entity-config-inheritance-example
    brooklyn.config:
      example.map:
        MESSAGE_IN_CHILD: InChild

- type: org.apache.brooklyn.entity.stock.BasicApplication
  name: app3
  brooklyn.config:
    example.map:
      MESSAGE_IN_PARENT: InParent
  brooklyn.children:
  - type: entity-config-inheritance-example

- type: org.apache.brooklyn.entity.stock.BasicApplication
  name: app4
  brooklyn.config:
    example.map:
      MESSAGE_IN_PARENT: InParent
  brooklyn.children:
  - type: entity-config-inheritance-example
    brooklyn.config:
      example.map:
        MESSAGE_IN_CHILD: InChild

A limitations of inheritance.runtime is when inheriting values from parent and grandparent entities: a value specified on the parent will override (rather than be merged with) the value on the grandparent.

Merging Policy and Enricher Configuration Values

A current limitation is that sub-type inheritance is not supported for configuration of policies and enrichers. The current behaviour is that config is not inherited. The concept of inheritance from the runtime management hierarchy does not apply for policies and enrichers (they do not have “parents”; they are attached to an entity).