Tier and Image Management

Intended for use with Cassatt Active Response V5.0.

After tiers are activated, changes to tier settings and images are inevitable. Although many of these tasks are intuitive and easy to perform using the Controller action menus, some tasks require explanation or have multiple steps.

This article describes things you should know when changing images and tiers:

Image = image version

Cassatt Active Response treats each version of an image completely independently from other versions. For example, when you select an image to delete, you are deleting only the selected version. For simplicity, this article uses the term "image" to mean an image version.

Images: delete

When an image—or any version of an image—is no longer needed in your Cassatt Active Response environment, you can delete it. Why delete an image? Images consume a lot of disk space. An average Linux image version takes 2.8 GB per base image + ~10% for each image instance.

Deleting a single version, including the original, does not affect any remaining versions. Before you can delete an image, you must deactivate it.

The Controller does not allow you to delete an image version when it is assigned to a tier, or while you are creating a new version from the version you wish to delete.

Never delete an image using a command such as rm; always delete an image from the Controller. Deleting an image while it is assigned to a tier or while it is being updated can disrupt services and leave behind clutter. The Controller has built-in guardrails to ensure deletion is safe and complete.

Images: update software, patches, or read-only properties

Whenever you need to change an image in a running tier (software version, patch, or change any of the image properties that are read-only), you must create a new version of the image. When you are ready to update a tier to the new version, Cassatt Active Response first boots one node with the updated software so you can test it. If you are satisfied with the update, Cassatt Active Response updates any remaining nodes in the tier. If you are not satisfied with the update (for example, your testing returns mixed results and the software requires further debugging), Cassatt Active Response reverts to the previous version of the software.

Follow these steps to update an image.

Step 1: Create a new version of the image

1. If you intend to delete an instance-specific directory from the new image, delete the directory from Images > image name > Properties before you begin. Configuration fails if you delete an instance-specific directory that is listed as required for the image.
   
2. Go to Images > image name (image you want to update.)
3. Choose Image Actions > New Version.
4. Click the New Version and enter a version number.
5. When the new version is complete, click Close. (Cassatt Active Response displays the Images page, with the new version of the image in the Image list.)
6. Select the checkbox for the new version of the image you just created.
7. Choose Image Actions > Configure Image.
8. On the Configure Image page, select the check box for one of the nodes listed from the free pool.
9. Click Boot. (Cassatt Active Response boots the image onto the selected node and displays the Configure Image page.)
10. Click Configure Later. The Controller displays the image list. The status for the new image version is "Configuring."
11. At this point, you can access the node (as specified by its IP address and rack/slot number) to modify the software or apply a patch.
12. When you are finished modifying the software, return to the Images page.
13. Select the new image version using the checkbox, and choose Image Actions > Configuration Complete.
14. Click Configuration Complete. (Cassatt Active Response releases the node back to the free pool.)
15. Reset any image properties as needed on the various image tabs.
16. With the image selected, choose Image Actions > Activate.
17. Click Activate. (Cassatt Active Response activates the image, making it available for assignment to tiers.)
18. You can configure the new version as many times as necessary until you are satisfied that the image is functioning as desired. You can also change image properties for the new version.
    
    

    When you are satisfied with the new version, you activate it to make it available for assignment to a tier.

    Image states: active and inactive Images have two states: active and inactive. Activating an image makes it available for assignment to a tier; deactivating an image prevents its assignment to a tier (for example, you might deactivate a malfunctioning image to prevent another user from using it before you can delete it). Cassatt Active Response sets images to active when you capture them so you can immediately assign a new image to a tier. You must explicitly activate new image versions.

Step 2: Update tier to use new image version (rolling update)

The Cassatt Active Response rolling update feature boots one application node for you to test, then sequentially reboots each node in the tier. Rolling update ensures that the tier services are not interrupted; if any node fails, Cassatt Active Response rolls back the entire update.

If you restrict hardware requirements in the new image version (for example, by requiring a larger local disk or more CPUs), Cassatt Active Response informs you when it finds any node that does not meet the new requirements. It does not replace the node. Whenever you restrict hardware requirements in a new image version, it is best to deactivate and deallocate the tier before following the update tier procedure. After the update is complete, reallocate the tier—Cassatt Active Response assigns only nodes that meet the new hardware requirements—then reactivate the tier.

Some applications are unsuited to rolling update because interrupting any node interrupts the entire service. For these applications, it is best to schedule downtime for the tier and deactivate it before following the update tier procedure. When you update a tier that is inactive, Cassatt Active Response updates all nodes in parallel after you accept the update on the test node. Check to see if your application supports rolling update.

Be aware that during a rolling update, Cassatt Active Response may (or may not) change servers in the tier. Cassatt Active Response allocates servers to unused image instances so it can update them; therefore, the tier may end up with different servers after a rolling update.

1. On the Tiers page, select the tier you want to modify.
2. Choose Tier Actions > Update Image.
3. In the New Tier Image drop-down menu, select the software image you want to run on the tier.
4. Select an application node or an image instance to use for testing the update. If you select an image instance, Cassatt Active Response boots an application node from the free pool to use as the test node. This keeps the tier working at the operational target while each application node is rebooted with the updated image. When all nodes are updated successfully, Cassatt Active Response returns the application node to the free pool. If you select an application node from the tier, the tier falls below the operational target during the time each node is rebooting, and Cassatt Active Response issues alerts describing the tier status.
5. Click Update.
   Cassatt Active Response compares the old and new image instances for the node. Files in the old image instances may conflict with files in the new image instances. The conflict may not occur on the test node, but on any later node. When Cassatt Active Response encounters a conflict, the Controller displays a list of conflicting files. Review the list and decide whether to preserve the old files or accept the new files. Cassatt Active Response does not allow individual selections. Select either Take New or Keep Existing; the selection applies to all of the files in the list. Cassatt Active Response rolls back the original upgrade and begins the tier image update again. Cassatt Active Response cycles through each node, including the test node and any others that were completed prior to encountering the conflicts. If Cassatt Active Response does not find conflicting files, Cassatt Active Response boots the application node with the new software image.
6. When the node is ready, validate that your software is running correctly.
   
   

   If software is...	Then...
   Running correctly.	Click Update. Cassatt Active Response updates one node at a time.
   Not running correctly.	Click Cancel. Cassatt Active Response reverts to the previous version of the software image.

   
   
7. When all nodes and image instances are updated, click Done.
8. If you've added a new instance-specific directory, you must add it to Images > image name > Properties after configuration so that Cassatt Active Response creates the new directories for each image instance.

Images: update settings

You can change some image settings when the image is running in a tier. The following tables describe the effects of changing image settings after an image is running in a tier.

Images > Properties

Images > Requirements

Images > Applications

Images: import and export

Cassatt Active Response provides import and export commands for moving images. For example, you can use ccexport and ccimport to move an image from test to production, or when you have more than one Cassatt Active Response environment that uses the same software for one of its tiers. Run the following commands as root from the control node:

• ccexport – packages the image and its image manifest (but no image instances) into a single tgz file.
• ccimport - unpacks the tgz file and stores the image and its manifest on the file system of your choice.
  

Tiers: update hardware requirements

To update hardware requirements for a tier that runs an image, follow these steps:

1. Deactivate and deallocate the tier: Tier Actions > Deactivate.
   Cassatt Active Response shuts down the nodes in the tier.
2. Tier Actions > Deallocate.
   Cassatt Active Response removes the application nodes from the tier.
3. Select the Requirements tab and change the settings as needed.
4. Allocate the tier by choosing Tier Actions > Allocate.
   Cassatt Active Response provisions the tier with application nodes.
5. Tier Actions > Activate.
   Cassatt Active Response starts up the nodes in the tier.

Tiers: update operational targets

You can increase or decrease the capacity (that is, the operational target number of nodes allocated to a tier), as long as the operational target is within the bounds of the minimum and maximum number of nodes.

To increase/decrease operational target of a tier:

1. Select the tier you want to modify.
2. Choose Tier Actions > Increase Capacity (or Decrease Capacity).

If increasing the target, the tier goes into a non-critical status while Cassatt Active Response searches for a node to add to the tier. If a node is available, the Controller allocates the node to the tier and the tier status returns to normal. If no node is available, the tier stays non-critical until a node becomes available or until you reduce the capacity.

After Cassatt Active Response has created a tier, you cannot modify the maximum number of nodes that can be allocated to the tier.

Tiers: update maximum nodes

Modifying maximum nodes in a tier requires some downtime. To incur the least amount of downtime, follow these steps to create a new higher-max tier while the current tier is running, then transfer services from the old tier to the new tier.

1. Create a new tier with the higher maximum using the same image.
2. If the image requires personalization, make sure the free pool contains the new maximum number of nodes by reducing the operational targets in the lowest priority tiers.
3. Set the operational target in the new tier low enough that you have sufficient application nodes in the free pool to allocate nodes to the new tier. (If you do not have sufficient application nodes in the free pool to allocate the minimum nodes to the new tier, reduce the operational target in your least crucial tier until the free pool contains enough application nodes.)
4. Activate the new tier.
5. Reduce the operational target in the old tier to the minimum; raise the operational target in the new tier to the desired level. Note: For the minimum service interruption, reduce the operational target in the old tier one application node at a time, and raise the operational target in the new tier one application node at a time. Wait for each node to move from the old tier, to the free pool, into the new tier, and become operational before initiating the next reduction.
   6. Reestablish the desired operational targets in any tiers from which you borrowed application nodes in earlier steps.
6. Deactivate and delete the old tier.

If you can afford downtime, deactivate all of your tiers, delete the old tier, create the new tier with the higher maximum (including personalization, if necessary), then reactivate your tiers.

Tiers: update image instances (personalization)

To change personalization on an image instance after the tier is running:

1. Select nodes in a tier.
2. Select Tier Actions > Personalize.
3. After you're done personalizing nodes, select Tier Actions > Personalization Complete.

Tiers: update settings using scripts

You may need to change tier settings for usage cycles such as month-end processing, and for unforeseen business challenges such as load spikes. Although you can change settings manually at any time through the Controller, you can make the changes programmatically through the Cassatt Active Response scripting SDK interface using Java, Visual Basic, Perl, or Shell. For standard usage cycles (daily, monthly, or some other known interval), you can write a fairly simple script to change SLAs on a set schedule. For a detailed scripting example, see the article Scripting Scheduled Configuration Changes for Cassatt Active Response.

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