This function helps you to get a list of all Cosmos DB accounts in some Azure Context and get the last time Accounts Keys has been updated and the number of keys updated.

Get-LastUpdateCosmosDBKeys.ps1

<#
.SYNOPSIS
    This function helps you to get a list of all Cosmos DB accounts in some Azure Context and get the last time Accounts Keys has been updated and the number of keys updated.
.DESCRIPTION
    It depends on Az PowerShell module, then it should be installed and you need to be logged into the account.
    To install and know more about Az PowerShell module, see: https://docs.microsoft.com/en-us/powershell/azure/new-azureps-module-az?view=azps-6.3.0#overview
    And then to authenticate you can use: Connect-AzAccount.
    If you want to use this function from Azure PowerShell then you don-t need to install or login.

.PARAMETER startTime
    Optional. It indicates the start time to look for Cosmos DB Key updates.
    By default, it is 1 year ago.
    You can use any valid date or just doing something like -startTime (Get-Date).AddMonths(-3)

.EXAMPLE
    Import function to the current PowerShell session:
    PS C:\> . C:\temp\PowerShellFunctions\Get-LastUpdateCosmosDBKeys.ps1
    Where C:\temp\ is the path where the file is.

.EXAMPLE
    Call without parameters:
    PS C:\> Get-LastUpdateCosmosDBKeys

    ResourceName          ResourceId                                                                                                     LastUpdate            ChangedKeys
    ------------          ----------                                                                                                     ----------            -----------
    jmbuserspoc           /subscriptions/subscriptionId/resourceGroups/group1/providers/Microsoft.DocumentDb/databaseAccounts/database1                        0
    jmbcosmosnotebookdemo /subscriptions/subscriptionId/resourceGroups/group2/providers/Microsoft.DocumentDb/databaseAccounts/database2  8/31/2021 11:47:00 PM 1

    It will get all Cosmos DB Key Updates from Current Context from the last year.

.EXAMPLE
    Call with -startTime parameter:
    PS C:\> Get-LastUpdateCosmosDBKeys -startTime (Get-Date).AddMonths(-3)

    ResourceName          ResourceId                                                                                                     LastUpdate            ChangedKeys
    ------------          ----------                                                                                                     ----------            -----------
    jmbuserspoc           /subscriptions/subscriptionId/resourceGroups/group1/providers/Microsoft.DocumentDb/databaseAccounts/database1                        0
    jmbcosmosnotebookdemo /subscriptions/subscriptionId/resourceGroups/group2/providers/Microsoft.DocumentDb/databaseAccounts/database2  8/31/2021 11:47:00 PM 1

    It will get all Cosmos DB Key Updates for the last 3 months.

.EXAMPLE
    Call with -startTime parameter:
    PS C:\> Get-LastUpdateCosmosDBKeys -startTime (Get-Date).AddMonths(-3)

    ResourceName          ResourceId                                                                                                     LastUpdate            ChangedKeys
    ------------          ----------                                                                                                     ----------            -----------
    jmbuserspoc           /subscriptions/subscriptionId/resourceGroups/group1/providers/Microsoft.DocumentDb/databaseAccounts/database1                        0
    jmbcosmosnotebookdemo /subscriptions/subscriptionId/resourceGroups/group2/providers/Microsoft.DocumentDb/databaseAccounts/database2  8/31/2021 11:47:00 PM 1

    It will get all Cosmos DB Key Updates for Current Context from the last 3 months.

.EXAMPLE
    Call with ContextName parameter:
    PS C:\> Get-LastUpdateCosmosDBKeys -ContextName 'My Context Name'

    ResourceName          ResourceId                                                                                                     LastUpdate            ChangedKeys
    ------------          ----------                                                                                                     ----------            -----------
    jmbuserspoc           /subscriptions/subscriptionId/resourceGroups/group1/providers/Microsoft.DocumentDb/databaseAccounts/database1                        0
    jmbcosmosnotebookdemo /subscriptions/subscriptionId/resourceGroups/group2/providers/Microsoft.DocumentDb/databaseAccounts/database2  8/31/2021 11:47:00 PM 1

    It will get all Cosmos DB Key Updates for context with Name 'My Context Name' from the last year.
    To check all Available context for your credentials, execute: Get-AzContext -ListAvailable | Select-Object -Property Name

.EXAMPLE
    Call with pipeline:
    PS C:\> PS C:\> Get-AzContext -ListAvailable | Get-LastUpdateCosmosDBKeys

    ResourceName          ResourceId                                                                                                     LastUpdate            ChangedKeys
    ------------          ----------                                                                                                     ----------            -----------
    jmbuserspoc           /subscriptions/subscriptionId/resourceGroups/group1/providers/Microsoft.DocumentDb/databaseAccounts/database1                        0
    jmbcosmosnotebookdemo /subscriptions/subscriptionId/resourceGroups/group2/providers/Microsoft.DocumentDb/databaseAccounts/database2  8/31/2021 11:47:00 PM 1

    It will get all Cosmos DB Key Updates for all available contexts from the last year.
    To check all Available context for your credentials, execute: Get-AzContext -ListAvailable | Select-Object -Property Name

.NOTES
    Author: Josué Martínez Buenrrostro
    Twitter: @josuemb

.LINK
    https://docs.microsoft.com/en-us/powershell/azure/new-azureps-module-az
    https://docs.microsoft.com/en-us/powershell/azure/context-persistence
    https://docs.microsoft.com/en-us/powershell/module/az.accounts/connect-azaccount
    https://docs.microsoft.com/en-us/powershell/module/az.accounts/get-azcontext
#>
function Get-LastUpdateCosmosDBKeys {
    [CmdletBinding()]
    param (
        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [Alias('Name')]
        [string] $ContextName = $null,
        [DateTime] $StartTime = (Get-Date).AddYears(-1)
    )
    PROCESS {
        if ($ContextName) {
            $context = Get-AzContext -Name $ContextName
        }
        else {
            $context = Get-AzContext
        }
        $subscriptionName = $context.Subscription.Name
        $updates = [System.Collections.ArrayList]@()
        Write-Progress -Activity 'Get-LastUpdateCosmosDBKeys' -Status "Getting Cosmos DB Accounts from Subscription ""$subscriptionName"""
        $cosmosDBAccounts = Get-AzResource -ResourceType 'Microsoft.DocumentDB/databaseAccounts' -DefaultProfile $context
        $currentCosmosDBAccount = 0
        $totalCosmosDBAccounts = ($cosmosDBAccounts | Measure-Object).Count
        foreach ($cosmosDBAccount in $cosmosDBAccounts) {
            Write-Progress -Activity 'Get-LastUpdateCosmosDBKeys' -Status "Getting last Key updates from Cosmos DB Accounts of Subscription ""$subscriptionName""" -PercentComplete ((($currentCosmosDBAccount++) / $totalCosmosDBAccounts) * 100)
            $metricsInfo = Get-AzMetric -MetricName UpdateAccountKeys -ResourceId $cosmosDBAccount.ResourceId -StartTime $StartTime -WarningAction Ignore -DefaultProfile $context
            $metrics = $metricsInfo.Data
            $lastUpdate = $null
            $changedKeys = 0
            if ($metrics) {
                $lastUpdateMetric = $metrics | Where-Object -Property Count -GT 0 | Sort-Object -Property TimeStamp -Descending | Select-Object -First 1
                $lastUpdate = $lastUpdateMetric.TimeStamp
                $changedKeys = $lastUpdateMetric.Count
            }
            $update = New-Object psobject
            $update | Add-Member -MemberType NoteProperty -Name 'ResourceName' -Value $cosmosDBAccount.ResourceName
            $update | Add-Member -MemberType NoteProperty -Name 'ResourceId' -Value $cosmosDBAccount.ResourceId
            $update | Add-Member -MemberType NoteProperty -Name 'LastUpdate' -Value $lastUpdate
            $update | Add-Member -MemberType NoteProperty -Name 'ChangedKeys' -Value $changedKeys            
            $updates += $update
        }
        return $updates
    }
}