Understanding Tier Configuration and Personalization

Intended for use with Cassatt Active Response V5.0.

Tiers are the main organizing mechanism in Cassatt Active Response for delivering shared resources. Tiers bring together images, networks, SLAs, policies, and monitoring collectors to provide a business service. This article provides guidance and best practices for:

• Preparing for tier creation
• Configuring tier settings
• Personalizing image instances on nodes
• Testing and tier activation

Preparing for tier creation

Configuring tiers is a balancing act—you must look at all tiers with their applications, all resources, and all SLAs so Cassatt Active Response handles flux to meet your needs. Before creating a tier, consider the following questions for each application running in your data center.

• What is the priority of the tier?
• Does the application impose hardware requirements that are different from the base image hardware requirements?
• How frequently is the application used?
• How many employees need access?
• Is usage steady over time, or does it fluctuate?
• Are usage cycles predictable?
• What level of availability is required?
• What networks do your applications require?

Prerequisites

Before creating tiers, make sure you:

• Create images for your business applications.
  See Understanding Image Creation and Capture.
• Configure networks (if using networks other than the Cassatt Active Response network). Most applications do not require special networking, but Cassatt Active Response supports many common networking scenarios for applications requiring specific network topologies (for example, the private interconnect required to run Oracle 10g RAC). You can also specify networks for a tier when you want to isolate the tier with firewall, or you want the tier to use specific IP addresses. See Understanding Cassatt Active Response Network Manager.
• Check blueprints to understand tier settings specific to your application.

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Configuring tier settings

This section describes each page in the New Tier wizard, and best practices for configuring tier settings. Although this section follows the page order of the wizard, several of the settings may need to be considered together.

Properties page

The Properties page contains these settings:

• Base image
• Email alerts
• Node failure rules
• Node harvesting

Base image

After a base image is captured, it is displayed in the Cassatt Active Response Controller in the Images tab. For example:

You can change base image properties to your heart's content until the point when you allocate nodes or activate the tier. After image instances are running in a tier, many of the base image properties are read-only. So, it's a good idea to refine your base image before activating the tier.

On the first page of the Tier mini-wizard, you assign a base image to a tier using a drop-down menu. At the end of tier creation, Cassatt Active Response creates image instances from the base image. For example:

Email alerts

You can choose to get email alerts whenever tiers are in critical and warning states. In both cases, Cassatt Active Response always tries to bring the tier back to normal; however, if your hardware reserves are stretched, and you if you've chosen to manually control some settings, you may need to keep a closer watch on resources. The bottom line is, the more you automate, and the more reserves you have, the less you need to be concerned about monitoring Cassatt Active Response, even when tiers are in critical or warning states.

Commas can be used to separate multiple email addresses in the Email Address text box.

Node failure rules

• Reboot on Failure – Your selection for this setting depends on the software running in the tier. For example, a reboot may be sufficient to restore normal operation when applications fail. Cassatt Active Response cannot automatically reboot nodes that do not have power controllers; select Off when your hardware requires a manual reboot.
• Automatic Move to Maintenance Pool – If you select On, Cassatt Active Response automatically moves failed application nodes from the tier to the maintenance pool. If two nodes fail after running the same image instance, Cassatt Active Response automatically disables that image instance so you can diagnose the problem. Meanwhile, Cassatt Active Response replaces the node—if a replacement is available—to keep the tier working at the operational target level. If you select Off, Cassatt Active Response disables the node, but leaves it in the tier so you can diagnose it with its current image instance.

Node harvesting

When resources are limited, nodes fail, or priorities change, Cassatt Active Response handles the unexpected with the Tier Priority and Allow Harvest settings. With Allow Harvest = On, Cassatt Active Response can appropriate application nodes from one tier when another tier is below its operational target (whether through a node failure or because you increased the operational target).

• Tier priority – if you are using node harvesting, you'll need to know your applications and set priorities across all tiers. Consider these definitions:
  
  
  • High – Availability and performance are crucial.
  • Medium – A drop in service level is acceptable to keep the high-priority tiers at optimal performance.
  • Low – Application is nonessential; significant drops in performance are acceptable. Note: Some level of availability is ensured; Cassatt Active Response never harvests tiers below minimum.
• Allow harvest – when a tier requires a node, Cassatt Active Response searches the free pool for a suitable replacement; if an appropriate node is not available in the free pool, Cassatt Active Response looks for suitable nodes in tiers that have node harvesting turned on. Cassatt Active Response then harvests nodes from tiers with:
  
  
  • A lower tier priority than the tier in need, or
  • An equal tier priority if the tier is deactivated, or the tier has more nodes than its minimum.

As you can imagine, the logic to handle every harvesting scenario is a bit more complex. For details on the logic behind node harvesting, see the sidebar Node harvesting logic.

To see an animated node harvesting example (that doesn't require any special software to run), see the sidebar Node harvesting animation.

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Requirements page

The Requirements page contains these settings:

• Node requirements
• Hardware requirements
• Custom attributes
• Tier dependencies
  

Node requirements

There are only three settings for node requirements, but careful attention must be given to these values.

• Operational target – preferred number of application nodes you want Cassatt Active Response to attempt to start and maintain in the tier.
• Minimum nodes – minimum number of application nodes required for the tier to provide service (the application to function).
• Maximum nodes – number of image instance "slots" to create for the tier.

The following graphic shows a tier running in a normal state, with image instances and node allocations based on target, minimum, and maximum.

Let's look at each setting in more detail.

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Operational target: what you should know

The operational target determines how many application nodes Cassatt Active Response attempts to run in each tier at any given time. Cassatt Active Response successfully keeps all tiers at their operational targets—as long as you have sufficient hardware The Controller lists fully allocated tiers with the normal status.

Whenever there isn't sufficient hardware to keep a tier at its operational target, Cassatt Active Response lists the tiers with the critical or warning status. In either case, the tier is operating below its operational target and is not fully compliant with its SLAs.

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Minimum nodes: what you should know

The minimum nodes setting is generally the absolute minimum required for the application to function. It can also be used to ensure a level of service that's above the absolute minimum required for the application to function. For example, if you have an agreement with a business unit that you will always supply a minimum level of performance for a set number of users, and you know that six nodes of the type specified for the tier are required to meet that service level, you can set your minimum to six.

Minimum nodes is the simplest capacity parameter to set. You can raise or lower the minimum nodes for a tier at any time.

Maximum nodes: what you should know

In general, the number you specify for maximum nodes will reflect the most nodes you foresee using for the tier, given maximum load. Although you could encounter an application with a practical maximum, you more likely will use the maximum to determine the number of image instances for Cassatt Active Response to create for the tier.

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Hardware requirements

Hardware requirements are set on the base image. However, you can set hardware requirements on the tier—which takes precedence over the hardware requirements set in the base image. This feature is used primarily for tweaking a tier. For example, an image may be configured for local disk. When you get real hardware in the tier, you may find that this is unnecessary and choose to turn off local disk for the tier.

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Custom requirements

Custom attributes are set on the base image. However, you can use custom attribute settings on a tier whenever you want hardware go to a specific tier. For example, say you purchased new IBM hardware that you wanted to go in a specific tier, you would set a custom attribute on the tier and the IBM node.

Cassatt Active Response allocates node with custom attributes last because they have the highest "cost." However, when resources are constrained, Cassatt Active Response does allocate nodes with custom attributes to tiers that do not require custom attributes.

Tier Dependencies

Some applications require other applications to be running in order to function properly. For example, imagine an enterprise-level order entry system with a 3-tier application stack: a database, an application server, and a web server. The application server can't do its job without the database, and the web server can't do its job without both of the other two.

You can set tier dependencies in Cassatt Active Response to help ensure that each application has the resources it needs—including availability of other applications. Setting a tier dependency in Cassatt Active Response ensures:

• The tier will activate properly by making sure all of the tiers it depends on are running before starting your tier.
• That neither you nor Cassatt Active Response can disrupt your tier operations by deactivating a tier that your tier depends on.

Cassatt Active Response disallows circular dependencies; that is, if tier "A" depends on tier "B," and you try to set tier "B" to depend on tier "A," Cassatt Active Response displays an error message.

Here's what you can expect to happen when you set one tier to depend on another. The next table uses two tiers as an example: an application server tier which depends on a database tier.

Some application blueprints in the Info Central blueprint library specify requirements for tier dependency settings. You can use blueprints as examples to help you understand when a tier dependency is required or useful.

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Networks page

If you are using just the Cassatt Active Response network, then that is the only network displayed on this page. Other networks are listed as a result of configuring networks in the Networks > New Networks wizard.

IPs and host names page

The IPs and host names page is displayed for each network that you select on the Networks page in the wizard.

The IP addresses and host names that you specify on this page are permanently assigned to the tier's image instances, but temporarily assigned to application nodes when nodes are allocated to the tier.

To assign a site-specific host name (not the same as the node name assigned by the Controller), specify either the host name prefix or the individual name of the node. (Cassatt Active Response displays as many text fields for host names as there are maximum nodes set for the tier.)

To use the "Provide via a file" option, create a file using the following format:

<IP_address>, <host_name>

Example:
10.10.73.9, dogmatic
10.10.73.10, system2
# This is a comment line.

Rules:
Use # for comment lines.
Blank lines are ignored.
Cassatt Active Response checks that the IP addresses are available on the network specified.
If one entry is invalid, Cassatt Active Response does not accept the file.

Personalizing image instances on nodes

At the end of the New Tier wizard, Cassatt Active Response creates image instances. Personalizing involves logging into each node in the tier and customizing the image instance for the specific application. If your application does not require personalization (check your blueprint or application), and you do not need to configure any external resources (as load balancers and SANs), you can skip this step.

The following table answers some common questions about personalization.

Testing and activating tiers

It's important to test and tweak tiers and images prior to activating the tier (when nodes in a tier are booted.) After image instances are running in a tier, many base image properties are read-only. To change read-only properties on a image, update software on the image, or add a patch, you must create a new version of the image.

Managing tiers and images

For help in changing tier settings and image properties after a tier is activated, see Tier and Image Management.

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