AWS Developer Blog

Improvements for AWS CloudFormation and Amazon CloudWatch in the AWS Tools for PowerShell Modules

Trevor Sullivan, a Systems Development Engineer here at Amazon, recently contributed some new AWS CloudFormation helper cmdlets and improved formatting for types he works with on a daily basis. These updates were released in version 3.3.119.0 of the AWS Tools for PowerShell modules (AWSPowerShell and AWSPowerShell.NetCore), in addition to new support in Amazon CloudWatch metrics for customizable dashboards. In this guest post, Trevor takes us through the updates.

Pause a script until a CloudFormation stack status is reached

If you want to pause your PowerShell script until a CloudFormation stack reaches a certain status, you can use the Wait-CFNStack cmdlet. You use Wait-CFNStack to specify a CloudFormation stack name and the status code that you want to wait for. All of the supported CloudFormation statuses are provided with IntelliSense/tab-completion for the -Status parameter, so you don’t need to look them up! Let’s take a look at how you use this cmdlet.

$Common = @{
    ProfileName = 'default'
    Region = 'us-east-2'
}
$CloudFormation = @{
    StackName = 'AWSCloudFormation'
    TemplateBody = @'
    AWSTemplateFormatVersion: '2010-09-09'
        Resources:
            myBucket:
                Type: AWS::S3::Bucket
        Outputs:
            BucketName:
            Value: !Ref myBucket
'@
}
New-CFNStack @CloudFormation @Common
Wait-CFNStack -StackName $CloudFormation.StackName @Common

Test the existence of the CloudFormation stack

Have you ever wanted to simply test whether a CloudFormation stack exists in a certain AWS Region? If so, we now have a cmdlet for that. The Test-CFNStack cmdlet simply returns a Boolean $true if the specified stack exists, or $false if it doesn’t. If your stack doesn’t exist, you no longer have to worry about catching exceptions thrown by the Get-CFNStack cmdlet!

$Common = @{
    ProfileName = 'default'
    Region = 'us-east-2'
}

if (Test-CFNStack -StackName $CloudFormation.StackName @Common) {
    Remove-CFNStack -StackName $CloudFormation.StackName –Force @Common
}

Format types

Another customer-obsessed enhancement in the latest version of the modules deals with the default display of certain objects. In earlier versions complex objects such as CloudFormation stacks were typically displayed in the vertical “list” format (see the Format-List PowerShell cmdlet). The “list” output format doesn’t use horizontal screen space very effectively. As a result, you have to scroll a lot to find what you want and the output isn’t easy to consume.

Instead, we opted to improve the default output to use the PowerShell table format. This makes data easier to consume, so you don’t have to scroll as much. It also limits focus to the object properties that you care about the most.

If you prefer the “list” format, you can still use it by piping your objects into the Format-List PowerShell cmdlet. The default output has simply been changed to use a tabular format to make data easier to interact with and consume.

The new format types work with cmdlets that emit complex objects, such as:

  • Get-CFNStackEvent
  • Get-CFNStack
  • Get-IAMRoleList
  • Get-CWERule
  • Get-LMFunctionList
  • Get-ASAutoScalingGroup
  • Get-WKSWorkspace
  • Get-CWAlarm

The changelog for version 3.3.119.0 of the module on the PowerShell Gallery lists all the types that new formats have been specified for. You can view the changelog for the release on the PowerShell Gallery.

Manage CloudWatch dashboards

AWS customers who use CloudWatch to store and view metrics will appreciate the new CloudWatch dashboard APIs. You can now use PowerShell cmdlets to create, list, and delete CloudWatch dashboards!

I’ve already created a CloudWatch dashboard in my account, so let’s check out how we can export it, modify it, and then update it. Let’s start by discovering which AWS cmdlets relate to CloudWatch dashboards by using Get-AWSCmdletName.

PS /Users/tsulli> Get-AWSCmdletName –MatchWithRegex dashboard

CmdletName           ServiceOperation         ServiceName       CmdletNounPrefix
----------           ----------------         -----------       ----------------
Get-CWDashboard      GetDashboard             Amazon CloudWatch CW
Get-CWDashboardList  ListDashboards           Amazon CloudWatch CW
Remove-CWDashboard   DeleteDashboards         Amazon CloudWatch CW
Write-CWDashboard    PutDashboard             Amazon CloudWatch CW

Now, let’s discover which CloudWatch dashboards already exist in the us-west-2 AWS Region by using Get-CWDashboardList.

PS /Users/tsulli> Get-CWDashboardList -Region us-west-2

DashboardArn   DashboardName   LastModified        Size
------------   -------------   ------------        ----
               MacBook-Pro     7/6/17 7:50:16 PM   1510

As you can see, I’ve got a single CloudWatch dashboard in my test account, with some interesting metrics about my MacBook Pro. Coincidentally, these hardware metrics are also being written to CloudWatch metrics using the AWSPowerShell.NETCore module.

Now let’s grab some detailed information about this specific CloudWatch dashboard. We do this using the Get-CWDashboard cmdlet, and simply passing in the region and name of the dashboard. Be sure to remember that the dashboard name is a case-sensitive input parameter.

PS /Users/tsulli> $Dashboard = Get-CWDashboard -DashboardName MacBook-Pro -Region us-west-2 | Format-List

LoggedAt : 7/7/17 1:44:44 PM
DashboardArn : arn:aws:cloudwatch::123456789012:dashboard/MacBook-Pro
DashboardBody : {"widgets......
DashboardName :
ResponseMetadata : Amazon.Runtime.ResponseMetadata
ContentLength : 3221
HttpStatusCode : OK

For readability in this article, I’ve trimmed the DashboardBody property. However, it contains a lengthy string with the JSON that represents my CloudWatch dashboard. I can use the ConvertFrom-Json cmdlet to convert the string to a usable object in PowerShell.

PS /Users/tsulli> $DashboardObject = $Dashboard.DashboardBody | ConvertFrom-Json

Now let’s update the title field of all the widgets on the CloudWatch dashboard. Let’s change the beginning of each widget’s title from “Trevor” to “David”. Right now, the title reads “Trevor’s MacBook Pro”. After updating it, the widget titles will read “David’s MacBook Pro”. We’ll use the ForEach method syntax in PowerShell to do this. Each widget has a property named //properties//, which has a //title// string property. We’ll do a simple string replacement operation on this property’s value.

PS /Users/tsulli> $DashboardObject.widgets.ForEach({ $PSItem.properties.title = $PSItem.properties.title.Replace('Trevor', 'David') })

Now that we’ve modified the widget titles, let’s convert the dashboard back to JSON and overwrite our dashboard! We’ll use ConvertTo-Json to convert the dashboard object back into its JSON representation. Then we’ll call Write-CWDashboard to commit the updated dashboard back to the CloudWatch service.

PS /Users/tsulli> $DashboardJson = $DashboardObject | ConvertTo-Json -Depth 8
PS /Users/tsulli> Write-CWDashboard -DashboardBody $DashboardJson -DashboardName MacBook-Pro -Region us-west-2

Great! Now if you go back to the AWS Management Console and visit your CloudWatch dashboard, you’ll see that your widgets have updated titles!

Conclusion

We hope you enjoy the continued improvements to the AWS Tools for PowerShell customer experience! If you have feedback on these improvements, please let us know. You can:

* Leave comments and feedback in our AWS SDK forums.
* Tweet to us at @awscloud and @awsfornet.
* Comment on this article!