Using Policies

Exploring and Testing Policies

To see an example of policy based management, please deploy the following blueprint (changing the location details as for the example shown earlier):

name: My Web Cluster

location: localhost


- type: org.apache.brooklyn.entity.webapp.ControlledDynamicWebAppCluster
  name: My Web
    wars.root: # BROOKLYN_VERSION
      brooklyn.example.db.url: >
        "visitors", "brooklyn", $brooklyn:external("brooklyn-demo-sample", "hidden-brooklyn-password"))
  - type: org.apache.brooklyn.policy.autoscaling.AutoScalerPolicy
      metric: webapp.reqs.perSec.windowed.perNode
      metricLowerBound: 0.1
      metricUpperBound: 10
      minPoolSize: 1
      maxPoolSize: 4
      resizeUpStabilizationDelay: 10s
      resizeDownStabilizationDelay: 1m

- type: org.apache.brooklyn.entity.database.mysql.MySqlNode
  id: db
  name: My DB
    creation.script.password: $brooklyn:external("brooklyn-demo-sample", "hidden-brooklyn-password")

The app server cluster has an AutoScalerPolicy, and the loadbalancer has a targets policy.

Use the Applications tab in the web console to drill down into the Policies section of the ControlledDynamicWebAppCluster. You will see that the AutoScalerPolicy is running.

This policy automatically scales the cluster up or down to be the right size for the cluster's current load. One server is the minimum size allowed by the policy.

The loadbalancer's targets policy ensures that the loadbalancer is updated as the cluster size changes.

Sitting idle, this cluster will only contain one server, but you can use a tool like jmeter pointed at the nginx endpoint to create load on the cluster. Download a jmeter test plan here.

As load is added, Apache Brooklyn requests a new cloud machine, creates a new app server, and adds it to the cluster. As load is removed, servers are removed from the cluster, and the infrastructure is handed back to the cloud.

Under the Covers

The AutoScalerPolicy here is configured to respond to the sensor reporting requests per second per node, invoking the default resize effector. By clicking on the policy, you can configure it to respond to a much lower threshhold or set long stabilization delays (the period before it scales out or back).

An even simpler test is to manually suspend the policy, by clicking "Suspend" in the policies list. You can then switch to the "Effectors" tab and manually trigger a resize. On resize, new nodes are created and configured, and in this case a policy on the nginx node reconfigures nginx whenever the set of active targets changes.


This guide has given a quick overview of using the Apache Brooklyn GUI to deploy, monitor and manage applications. The GUI also allows you to perform various Advanced management tasks and to explore and use the REST API (from the Script tab). Please take some time now to become more familiar with the GUI.

Then continue to read through the Operations Guide.

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