AWSPowerShell: When Possible, Cmdlets Should Fail Immediately if a Region is not Specified.

[bgshacklett]

Expected Behavior

If a Cmdlet which requires a region is executed and no region is specified, either by persistent means, shell defaults, or parameter, the Cmdlet should throw an error.

Current Behavior

The Cmdlet will hang for 15 seconds. Some Cmdlets (Get-CfnStackResource, for instance) cannot be killed with ^C

> measure-command {get-ec2instance}
...
get-ec2instance : No region specified or obtained from persisted/shell
defaults.
...
Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 15
Milliseconds      : 820
Ticks             : 158205674
TotalDays         : 0.000183108418981481
TotalHours        : 0.00439460205555556
TotalMinutes      : 0.263676123333333
TotalSeconds      : 15.8205674
TotalMilliseconds : 15820.5674

Possible Solution

Unfortunately, I don't have the visibility into why the current behavior exists, which makes it difficult for me to suggest a resolution. I would, however, suggest keeping "fail fast" in mind.

Steps to Reproduce (for bugs)

1. Ensure that no region is configured via persisted or shell default mechanisms
2. Initialize the authentication variables
   • AWS_SESSION_TOKEN
   • AWS_ACCESS_KEY_ID
   • AWS_SECRET_ACCESS_KEY
3. Run Get-Ec2Instance with no parameters.

Context

If I forget to specify a region, it can be up to 15 seconds for the command to time out and allow me to fix my mistake. Fast iteration on command execution is impeded, and it causes frustration.

Your Environment

Platform : Win32NT ServicePack : Version : 10.0.14393.0 VersionString : Microsoft Windows NT 10.0.14393.0

PSVersion 5.1.14393.1480
PSEdition Desktop
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0, 5.0, 5.1.14393.1480}
BuildVersion 10.0.14393.1480
CLRVersion 4.0.30319.42000
WSManStackVersion 3.0
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1

[PavelSafronov]

The reason for the slow execution is that the cmdlets try to get the region from the environment, including the EC2 Instance Metadata, which entails making an HTTP request. The request has a 5 second time-out, and we retry this up to 3 times, which is the 15 second slow-down that you are seeing.

To avoid situations like this we recommend setting a region globally for all cmdlets.

[bgshacklett]

Is there nothing that can be done to detect whether it's running on an EC2 instance in a shorter period of time? I understand your perspective, but most of the time that I make use of the AWS PowerShell module, it's on a management workstation outside of the AWS environment.

Additionally, I understand that the Set-DefaultAWSRegion Cmdlet exists for a reason, but it can be painful to use this when jumping from account to account, as there's no real feedback as to when it's set, and commands may be run in the wrong region accidentally.

[PavelSafronov]

Identifying if a given instance is or is not EC2 is a very complex question and one that we haven't found a satisfactory answer to yet.

[bgshacklett]

What about a configuration item which could be set in a user's profile to disable the instance metadata search? It's hackish, but it's a start.

[PavelSafronov]

The PowerShell cmdlets are built on top of the .NET SDK, and that's where the logic is located (source). So while this is in theory possible, it would be a somewhat complex change. We'll brainstorm on this internally a bit.

[PavelSafronov]

We've added this as a feature request onto our PowerShell backlog.

[stevejroberts]

While we determine what best to d, here's something I use in my profile to help me maintain visually what credential and region context I am currently in:

function prompt
{
    $realLASTEXITCODE = $LASTEXITCODE
    $prompt = ""
    Try
    {
        if ($StoredAWSCredentials -ne $null)
        {
            $prompt += "$StoredAWSCredentials"
            if (!$prompt.EndsWith("@")) { $prompt += "@" }
        }
        if ($StoredAWSRegion -ne $null) { $prompt += "$StoredAWSRegion" }
        $prompt += " "
    }
    Catch
    {
        $prompt = "PS "
    }

    $prompt += $pwd.ProviderPath
    $prompt +=
@"

>
"@

    $global:LASTEXITCODE = $realLASTEXITCODE
    $prompt
}

[bgshacklett]

I'm doing something similar now using the posh-git module, which has a convenience feature to set the prompt (setting $GitPromptSettings.DefaultPromptSuffix).

[ashishdhingra]

Hi @bgshacklett,

Good afternoon.

I was going through the backlog and came across this issue. As mentioned in the https://github.com/aws/aws-tools-for-powershell/issues/10#issuecomment-319796231, region detection involves searching in the predefined locations. I'm not sure of a work around which would disable EC2 Instance Metadata search at this stage. Hope this helps.

Please confirm if could close this issue.

Thanks, Ashish

[bgshacklett]

Seems like there's no easy fix. Thanks for looking into it. I'm onboard with closing it out.

[sgupta07]

AWSpowershell retries 3 times for all command ? is there a way we can change this setting like aws cli ?