Effectors perform an operation of some kind, carried out by a Brooklyn Entity. They can be manually invoked or triggered by a Policy.
Common uses of an effector include the following:
Entities have default effectors, the lifecycle management effectors like start, stop, restart, and clearly more Effectors can be attached to them.
Effectors are highly reusable as their inputs, thresholds and targets are customizable.
An Effector to invoke a command on a node accessible via SSH.
It enables execution of a command in a specific execution director (executionDir) by using a custom shell environment (shellEnv). By default, the specified command will be executed on the entity where the effector is attached or on all children or all members (if it is a group) by configuring executionTarget.
There are a number of additional configuration keys available for the SSHCommandEffector:
| Configuration Key | Default | Description |
|---|---|---|
| command | command to be executed on the execution target | |
| executionDir | possible values: ‘GET’, ‘HEAD’, ‘POST’, ‘PUT’, ‘PATCH’, ‘DELETE’, ‘OPTIONS’, ‘TRACE’ | |
| shellEnv | custom shell environment where the command is executed | |
| executionTarget | ENTITY | possible values: ‘MEMBERS’, ‘CHILDREN’ |
Here is a simple example of an SshCommandEffector definition:
{% highlight yaml %} brooklyn.initializers:
See here for more details.
An Effector to invoke HTTP endpoints.
It allows the user to specify the URI, the HTTP verb, credentials for authentication and HTTP headers.
There are a number of additional configuration keys available for the HTTPCommandEffector:
| Configuration Key | Default | Description |
|---|---|---|
| uri | URI of the endpoint | |
| httpVerb | possible values: ‘GET’, ‘HEAD’, ‘POST’, ‘PUT’, ‘PATCH’, ‘DELETE’, ‘OPTIONS’, ‘TRACE’ | |
| httpUsername | user name for the authentication | |
| httpPassword | password for the authentication | |
| headers | application/json | It explicitly supports application/x-www-form-urlencoded |
| httpPayload | The body of the HTTP request | |
| jsonPath | A jsonPath expression to extract values from a JSON object | |
| jsonPathAndSensors | A map where keys are jsonPath expressions and values the name of the sensor where to publish extracted values |
When a the header HttpHeaders.CONTENT_TYPE is equals to application/x-www-form-urlencoded and the httpPayload is a map, the payload is transformed into a single string using URLEncoded.
{% highlight yaml %} brooklyn.initializers:
See here for more details.
An Effector to add a child blueprint to an entity.
{% highlight yaml %} brooklyn.initializers:
type: org.apache.brooklyn.core.effector.AddChildrenEffector brooklyn.config: name: add_tomcat blueprint_yaml: | name: sample description: Tomcat sample JSP and servlet application. origin: http://www.oracle.com/nCAMP/Hand services: - type: io.camp.mock:AppServer name: Hello WAR wars: /: hello.war controller.spec: port: 80
brooklyn.catalog:
name: catalog-name
type: io.camp.mock.MyApplication
version: 0.9
libraries:
- name: org.apache.brooklyn.test.resources.osgi.brooklyn-test-osgi-entities
version: 0.1.0
url: classpath:/brooklyn/osgi/brooklyn-test-osgi-entities.jar
auto_start: true {% endhighlight %}
One of the config keys BLUEPRINT_YAML (containing a YAML blueprint (map or string)) or BLUEPRINT_TYPE (containing a string referring to a catalog type) should be supplied, but not both.
See here for more details.
Effectors generally perform actions on entities. Each effector instance is associated with an entity, and at runtime it will typically exectute an operation, collect the result and, potentially, publish it as sensor on that entity, performing some computation.
Writing an effector is straightforward. Simply extend AddEffector, providing an implementation for newEffectorBuilder and adding a constructor that consumes the builder or override an existing effector.
{% highlight java %}
public MyEffector(ConfigBag params) { super(newEffectorBuilder(params).build()); }
public static EffectorBuilder newEffectorBuilder(ConfigBag params) { EffectorBuilder eff = AddEffector.newEffectorBuilder(String.class, params); eff.impl(new Body(eff.buildAbstract(), params)); return eff; } {% endhighlight %}
and supply an EffectorBody similar to:
{% highlight java %}
protected static class Body extends EffectorBody { ...
@Override
public String call(final ConfigBag params) {
...
}
} {% endhighlight %}
The following recommendations should be considered when designing effectors:
One effector which executes a command and emits a sensor, and a second effector which uses the previous sensor, if defined, to execute another operation.