Rackspace Auto Scale Control Panel User Guide - Creating Scaling Policies


In the previous section (Creating Scaling Groups), you learned how to set the parameters for scaling policies through scaling group configuration. In this section we will discuss the Auto Scale current policy options and how group configurations affect policy execution. A scaling policy determines what actions are taken, on your scaling group and when they are taken. You can create scaling policies for an existing scaling group at any time by returning to the group configuration page. Typically, you will want at least two policies, one to scale up and one to scale down. You can create up to 1000 policies per group.

There are two parts to creating scaling policies:

Once you have set up your Auto Scale, you may be interested in Next Steps.

Create a Scaling Policy

  1. On the Create Scaling Group page, click Create Policy.

    A dialog box opens with policy options.

  2. In the dialog box that appears, select the following values:
    • Name: Specify a name for the policy, for example, “Scale up by 10 on Fridays at 5p.m.”
    • Scale Trigger: For Rackspace Auto Scale version 1, the only option is Recurring Schedule. This option means that servers will scale up or down on a set, recurring schedule (for example, every day at 6 p.m.). Depending on whether or not you selected Scheduled (cron) or Scheduled (repeating), specify the schedule as follows:
      • Scheduled (repeating): Specify how often the policy will occur and when.
      • Scheduled (once): Specify when the policy will occur.
      • Scheduled (cron): Enter a cron expression. You can click Cron Expression Helper to open a new tab to a Cron expression helper and generate a cron expression; use the tabs at the top if necessary. Then copy the expression into Auto Scale.
      • Webhook URL: Specify that the policy will use a webhook. You must create and configure the webhook using the Auto Scale API. For details on doing this, see the Auto Scale API Developer's guide, Webhooks chapter.
    • Amount: Select Scale Up or Scale Down, enter an integer, and select Servers or Percent. If you specify Scale Up by 2 Servers, the policy will add two servers to your scaling group when the policy is triggered. If you specify Scale Up by 2 Percent, the policy will add servers to equal the equivalent of two percent of your current scaling group, whatever size it is. See Scale Up by Percentage Policy for a visual explanation.
    • Cooldown Period: The policy cooldown, like the group cooldown, prevents a policy from being executed too frequently. For schedule-based policies, we advise leaving this value empty or setting it to 0 (zero).

      Two examples of scaling policies are shown in the following screen captures. The first shows a scale up policy using a cron expression. The second shows a scale down policy using a set, monthly, schedule.

  1. Click Save.
    The dialog box closes and the scaling policy that you created is added to the list of scaling policies on the Create Scaling Group page.

 

Test Your Configuration

After you create a scaling group, in addition to checking the status and animated gifs showing deployment, you can test your configuration by changing the minimum number of entities for the group and watching the new server or servers being added.

Next Steps

Now that you have created a scaling group and policy, following are some next steps that you might take:

     


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