Using Stack Auditor in TAS for VMs

Stack Auditor is a cf CLI plug-in that allows you to list apps and their stacks, migrate apps to a new stack, and delete a stack. Learn how to use it on this page.

One use case for Stack Auditor is when you must migrate a large number of apps to a new stack. This includes moving from cflinuxfs2 to cflinuxfs3 in preparation to upgrade your deployment to a version that does not contain cflinuxfs2. The following table describes the workflow you can use:

Stage	Description
1	Operator audits stack usage to determine which apps need to be migrated. See List apps and their stacks.
2	Operator communicates with developers that they must migrate their existing apps to a new stack and begin pushing all new apps to the a new stack.
3	Developers migrate their apps to a new stack. See Change stacks.
4	Operator confirms apps have been migrated.
5	Operator deletes buildpacks associated with the old stack.
6	Operator deletes the old stack. See Delete a stack. Note: If you upgrade your deployment to a version that contains the stack you deleted, the stack returns on upgrade.
7	If applicable, operator upgrades the deployment to the version that does not contain the old stack.

Install Stack Auditor

To install Stack Auditor, do the following:

Download the Stack Auditor binary for your OS from Buildpack Extensions on VMware Tanzu Network.
Unzip the binary file you downloaded:
```
tar xvzf PATH-TO-BINARY
```
Install the plugin with the cf CLI:
```
cf install-plugin PATH-TO-BINARY
```

Use Stack Auditor

The sections below describe how to use Stack Auditor.

List apps and their stacks

This section describes how to see the apps in each org and space and what stack they are using.

To see which apps are using which stack, run the following command. It lists apps for each org you have access to. To see all the apps in your deployment, ensure that you are logged in to the cf CLI as a user who can access all orgs.

cf audit-stack

See the following example output:

$ cf audit-stack
first-org/development/first-app cflinuxfs2
first-org/staging/first-app cflinuxfs2
first-org/production/first-app cflinuxfs2
second-org/development/second-app cflinuxfs3
second-org/staging/second-app cflinuxfs3
second-org/production/second-app cflinuxfs3
...

Change stacks

This section describes how to change the stack that an app uses. Stack Auditor rebuilds the app onto the new stack without a change in the source code of the app. If you want to move the app to a new stack with updated source code, follow the procedure in the Changing Stacks topic.

Warning: After successfully staging the app on cflinuxfs3, Stack Auditor attempts to restart the app on cflinuxfs3. This causes brief downtime. To avoid this brief downtime, use a blue-green strategy. See Using Blue-Green Deployment to Reduce Downtime and Risk.

To change the stack an app uses, do the following:

Target the org and space of the app:
```
cf target ORG SPACE
```
Where: * ORG is the org the app is in * SPACE is the space the app is in

Run the following command:

Note: If the app is in a stopped state, it remains stopped after changing stacks.

Note: When attempting to change stacks, your app is stopped. If the app fails on cflinuxfs3, Stack Auditor attempts to restage your app on cflinuxfs2.

cf change-stack APP-NAME STACK-NAME

Where: * APP-NAME is the app that you want to move to a new stack * STACK-NAME is the stack you want to move the app to

See the following example output:

$ cf change-stack my-app cflinuxfs3
Attempting to change stack to cflinuxfs3 for my-app...
Starting app my-app in org pivotal-pubtools / space pivotalcf-staging as ljarzynski@pivotal.io...
Downloading staticfile_buildpack...

. . .

requested state: started
instances: 1/1
usage: 64M x 1 instance
urls: example.com
last uploaded: Thu Mar 28 17:44:46 UTC 2019
stack: cflinuxfs3
buildpack: staticfile_buildpack

	 state     since                    cpu    memory        disk         details
#0   running   2019-04-02 03:18:57 PM   0.0%   8.2M of 64M   6.9M of 1G


Application my-app was successfully changed to Stack cflinuxfs3

Delete a stack

This section describes how to delete a stack from your deployment. You must be an admin user to complete this step.

To delete a stack, run the following command. This action cannot be undone, with the following exception: If you upgrade your deployment to a version that contains the stack you deleted, the stack returns on upgrade.
```
cf delete-stack STACK-NAME
```
Where STACK-NAME is the name of the stack you want to delete.
```
$ cf delete-stack cflinuxfs2
Are you sure you want to remove the cflinuxfs2 stack? If so, type the name of the stack [cflinuxfs2]
>cflinuxfs2
Deleting stack cflinuxfs2...
Stack cflinuxfs2 has been deleted.
```
If you have any apps still running on cflinuxfs2, the command returns the following error:
```
Failed to delete stack cflinuxfs2 with error: Please delete the app associations for your stack.
```