From AWS System Manager Document to Linux EC2 PowerShell Script

Let me start from what I'm trying to accomplished. Basically, I need to map partitions in Linux with EBS volumes. I first tried "df" command which works great. Through the following article, I found a way to retrieve corresponding volumes attached to the EC2 instance.

https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ec2-windows-volumes.html

Next, it is just a matter to marry both of them and output them as json. After many web searches and pages, I decided to install PowerShell Core to utilize its ConvertTo-Json function. All went great and I would like to create a new AWS System Manager Command Document so I can fire up an api call to execute the script.

I first tried AWS System Manager's RunPowerShellScript document which claims to be able to execute PowerShell script on Linux. However, it somehow failed. I checked the requirements, update SSM Agent to no avail. Eventually, we submitted support ticket and waiting for the reply.

While waiting for the support reply, I found a workaround. The RunShellScript document works fine and PowerShell supports running command as argument, so I tried:

pwsh -Command "<the_command>"

And it failed. Through trial and error, I found out that I need to escape the $ sign on the document side. I then tried again. And of course, it failed again.

Next, I remembered that double quotes needs to be escaped in the document. However, it can create confusion on the execution side, so it has to be escaped the second time for PowerShell argument.

On the document, it becomes:

" pwsh -Command \"\$PS_Variable=\\\"Intended String\\\"\""

The double escape works for the double quotes, but it is troublesome, so I decided to change the internal double quotes to single quote because PowerShell can handle it too and no escape needed.

" pwsh -Command \"\$PS_Variable='Intended String (cleaner, no?)'\""

However, I found out another issue, single quote does not handle insert of variable and thus for my case, it still failed.

" pwsh -Command \"\$PS_Variable='This does work'\""

" pwsh -Command \"\$PS_Variable='NOT' \$YetAnotherVariable='This does \$PS_Variable work'\""

Well, it is easy, just return it to double-escaped double quotes.

Next, I had another issue that it is unable to access AWS API. After another set of trials and errors, I found out that I need to import AWS Powershell module in the document, thus I have to add the following line:

" Import-Module AWSPowerShell.NetCore"

or shorthand:

" ipmo AWSPowerShell.NetCore"

And now it is 5 and works perfectly.

Edit 10/26/2018: AWS support replied that there is indeed an issue with the RunPowerShell script command.

Edit 11/01/2018: AWS support said the internal team were able to replicate the issue and working on the fix. No ETA as of today.

PowerShell Split String by Whitespaces or Multiple Spaces Using Regex

I was looking into a way to split string that can take regular expression in PowerShell. Surprisingly, they have the capability:

$StringArray = $StringInput -split '\s+'

Invoke-WebRequest PowerShell Command through Amazon AWS System Manager

I had a small issue with running Invoke-WebRequest through Amazon AWS System Manager. Somehow it doesn't seem to load the module properly.

I ended up replacing:

Invoke-WebRequest -Uri <url>

with:

$WebClient = New-Object System.Net.WebClient
$WebClient.DownloadString(<uri>)

which works perfectly for my case.

UNC and URL

Found something weird today. For a long time, we have published our project to the test environment using the following UNC pattern: \\testservername.productiondomain.com\shared-path. However, when I did that today, it accidentally connected to production.

Removing the domain as part of the UNC solves the problem. The weird thing is the same UNC points to our test environment when run on my coworker's computer. Nothing is weird on our hosts file.

I have not figured out why this is so. This post thus will be updated once I found out the actual reason.

Entity Framework Sorting/ Ordering and Dynamic LINQ

One of my coworkers would like me to update my IEnumerable SortBy extension method to support multiple columns. As I was working on it, I stumbled upon a nice StackOverflow question on Dynamic LINQ OrderBy on IEnumerable<T> and also Dynamic LINQ.

They are all awesome. I decided to try Dynamic LINQ by adding it through Nuget. However, I soon found that Dynamic LINQ only support property names. In some cases, we want to be able to sort by specifying column attribute value, so I still use my own code which works just fine although it might not be optimized for performance.

For example in VB.NET:

Public Class Customer
    <Column c_name="">
    Public Property Name As String

    <Column c_age="">
    Public Property Age As Integer
End Public

Dim sortedByName = dbContext.Customers.AsEnumerable().SortBy("c_Name, c_Age DESC")

The gist for my code can be found in:
https://gist.github.com/nikyodo85/202fc2d417d9eb030d30896ccc862b7d