PowerShell and GitLab CI – Part 5

Introduction

During the last article in this series on the use of PowerShell with GitLab, we noticed some displays on the build console, and some results from our build that was a bit unusual.

Today, I’m going to look a bit further into how the build engine works, which will also explain some of these results we are seeing.

How GitLab CI Runner Works

It would be logical to think that the PowerShell code is run in the same location or a subdirectory of the folder where the service file is, similar to Jenkins, but after a bit of investigation, I found out this is not the case.

To look further into what was happening, let’s add a line to the script section of the YAML file, and put a Start-Sleep command in.Make it ten minutes, to give enough time to remote onto the GitLab CI Runner, and do a search for our .ps1 file stored in a subdirectory of the repository.

Use the content below for our build file.

  • Save the changes
  • Add the updated file
  • Commit the changes
  • Push the changes
  • Navigate to the build section
  • Click on the commit

The job is running, and because of the Start-Sleep command, will continue to do so for the next ten minutes.

Part 5 - GitLab Job Running

Discoveries

  • Remote onto your build server (if it is not already the same system you are accessing GitLab from.
  • Go to the C:\Windows\Temp

There will be a folder name of the format Build_xxxxPart 5 - Temp Dir

  • Double click on the folder

Part 5 - Build Script Contents Dir

  • Within this folder is a script.ps1 file.
  • Open the file

Part 5 - The Script Code

The PowerShell code contained within the script: section of the YAML file is adjusted to make it suitable for returning the output we can see on the console window within a Gitlab job.

Looking at the code now, we can see that it has been changed significantly :

  • ErrorActionPreference has been set to ‘Stop‘.
  • Commands are in place to check to see if an error has occured, and if so to exit the script.  This will also result in the job being flagged as having failed.
  • Probably the most interesting of the changes is the frequent use of Echo command which mimics the command that follows it.

This explains several things to us :

  • How the console output is seen on the job screen
  • Some lines output appeared strange because variables were undefined at the stage when the Echo command ran

Because PowerShell returns all output from a function, it explains why were receive an array when the HappyHelloWorld function is called. It consists of the intented output, but also the Echo commands.

The use of a function in our build code now becomes a challenge or possibly could be perceived as something to be avoided, since we cannot guarantee the element in the array that will contain our desired output.  One way i’ve been able to get round this is to make the function return a PScustomobject, and make use of the -is operator outside of the function to obtain the value.

e.g. $functionOutput = $arrayReturned | Where {$PSItem -is [pscustomobject]}

However, I’ve found a better approach is to minimize the actual PowerShell commands that you use in the script, and instead create a Build folder within your repository which contains files with the actual commands that you wish to use for the build. These can be dotsourced to make them available from within the script, without the need for adding custom code to handle this.

There are many other aspects and configuration settings possible within GitLab, which lets you have powerful control over your build steps. Examples of this are defining the order of execution, ignoring errors, and setting the steps to be taken after each one.

It’s also worthwhile noting that these articles do not include the use of testing, which should be part of your chain of operations. If you are not already familiar with the use of Pester, I’d recommend taking a look at the documentation and examples on GitLab. Amongst others, Jakub Jareš has also written an excellent series of articles on its use, which you can find on PowerShellMagazine.com

That’s it for this series of articles on the use of PowerShell and GitLab. Thanks for reading, and feel free to provide feedback.

cheers,

Tim

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PowerShell and GitLab CI – Part 4

Part 3 of this series on using PowerShell and GitLab CI gave us an initial insight into how to setup and run PowerShell code as part of a build script. During it, we were introduced to the YAML build file, .gitlab-ci.yml.

This article, and the following one will cover some of the gotchas I’ve encountered whilst getting to grips with this file, and how to get these working as you’d expect. Hopefully these will help save you some time setting these up.It will also touch on some oddities you might experience creating build scripts.

Overview

At this point, I’m going to continue to use the same project with the same job name, even though it will deviate from the original script we created earlier. This is to allow us to go through the situations I’ll mention slightly faster, and I’ll indicate for each example what the subject is about. Let’s begin!

Keep Things in Line

The YAML specification demands a bit extra attention to formatting of your build scripts. Keep your ‘-‘ and labels in line.

Fails

gitlab commit 1

Succeeds

gitlab commit 2

Don’t use the TAB character

Unless you are using an editor which automatically translate the use of the TAB key into spaces, your scripts will fail. Use normal spaces.

Fails

The script below, whilst appearing indentical to the one that succeeds, uses table characters for indentation.

gitlab commit 3

Succeeds

gitlab commit 4

Watch Out For ScriptBlocks

The formatting for the use of a scriptblock can sometimes be a bit confusing. The final brace that closes the scriptblock should not have a ‘-‘ prefixing it. Additionally, if there is only one line of code within the scriptblock, it is not neccessary to use this prefix (but see below)

Fails

gitlab commit 5

Succeeds

gitlab commit 6
And if we actually look a the build output, we will see the details.
You might be quite correctly thinking that something looks a bit unusual with the output. This will be covered shortly……..

gitlab commit 7

And a look at helloworld.txt to make sure it has worked correctly.
gitlab commit 8

You Must Use ‘-‘ For Any Code Within Braces If It Consists of More Than One Line

If you have any code that surrounds itself in braces, such as a scripblock, function, or reiteration action, it will execute successfully without using the ‘-‘ character if there is only one line. However, two or more lines of code will fail.

Fails

Succeeds

It is probably best to start using ‘-‘ even with one single line within braces.

The script works, but the output on the screen is even stranger!
gitlab commit13

But the results are good….
gitlab commit14

Watch for error handling

Watch your syntax if you are wanting to use a Try..Catch block
Also, code within

Fails

gitlab commit18

Succeeds

gitlab commit19

So the script has successfully executed. Again, the output on the screen is a bit strange, but let’s check the helloworld.txt file out.

gitlab commit20

However, the file itself has not been created, despite the fact that we know this should raise a division by zero error, which should mean the catch scriptblock is executed.

Functions Behave Differently Than You Would Expect

This final part is the greatest challenge i’ve come across so far, and deserves a bit extra detail. It will also be covered further in the next article in this series.

Let’s modify the build script more. Here’s the PowerShell we’re going to use :

Here, we’ve modified our build script by adding a function which returns a string, and then output it to the same text file we’ve been using previously. If you want, you can verify the PowerShell code in the ISE, and also that the helloworld.txt file has been successfully created.

This would be put into our build script like this :

And it builds successfully
gitlab commit15

So let’s take a look at helloworld.txt
gitlab commit16

This is strange!!! There is other items there that shouldn’t be. In fact, only the last line of the file should be there.

Let’s do a bit of detective work and see if we can get more information about what’s being returned. A good starting place would be to see if we are getting a multiline string or an array returned.

So let’s take a look at helloworld.txt
gitlab commit17

This is real strange, an array is being returned. But we know that only a string is returned from the function. In the next article, we’ll dig deeper into what’s actually happening during the build process, which will shed some light on some of the strange things we’ve been noticing. Then we’ll also take a look at Lint, and how we can use it carry out checking of our YAML files.

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PowerShell and GitLab CI – Part 3

In part 1, and part 2 of this series, we covered the installation and configuration of pre-requistites, setting up our GitLab account and initial settings, and finally getting our Windows Runner installed and operational.

Today’s, I’ll give an overview of how GitLab uses build configuration files, how it is constructed, and setup our project in preparation for getting our first build complete.

GitLab Build Conifiguration

Previously, I’d been using Jenkin’s for my CI system, and immediately noticed how build configuration is different. With GitLab CI, the build file itself, .gitlab-ci.yml, is actually part of the repository. No webhook setup is necessary.

We also now have capabilities, such as not only having a dedicated runner per project, but per branch of our project, which we can control and manage directly from our repo.

Create a Demo PowerShell Script

Let’s setup a really simple script which we want to pass through the CI Engine.

  • Log back into the GitLab environment
  • Open your project

git - part 4 - 1 - login to git

Now launch the PowerShell ISE, and make the following script:

Save the file as HelloWorld.ps1 into the root of your repository (C:\temp\helloworld in my case)

Commit and Push to GitLab

We’ve added content to the repository, so lets go ahead and push the changes to GitLab.

  • Start a Bash session
  • Set your current current directory to the root of your repository
  • Enter the commands below

git - part 4 - 3 - pushing our changes

Now return to GitLab, and select Commits to confirm the commit has occurred.

Results

To the right of the commit, you will see a red ‘x’ mark. You might think that this is an options to delete the commit that has been made, but it’s something else entirely.

git - part 4 - gitlab commit screen

Click on the red cross. Looking further down the screen we see an error message.

Found errors in your .gitlab-ci.yml:
Undefined yaml error
.gitlab-ci.yml not found in this commit

git - part 5 - gitlab commit and build details screen

As mentioned, .gitlab-ci.yml is the build file that stored within the repository itself. The commit has been successfully placed into source control, but because we enabled CI for this project, GitLab has also expected the build file to exist.

A Quick bit About YAML and gitlab-ci.yml

We’re now at the stage where we are wanting to design our build configuration file for the helloworld project.

Build actions for GitLab projects are stored within a file, .gitlab-ci.yml, which is placed in the root of a repository. This file uses YAML format, and describes the build actions and criteria. Those of you familiar with AppVeyor may be aware of this format of file, and the requirements it has to be successfully parsed.

You can read more about YAML on WikiPedia, and other sources.

As a newbie I struggled with this file, and it took me a whole day before I was able to get a successful build to occur (though it wasn’t helped by my build script being quite longer than our example). I’ll cover this file in a bit more detail, and the gotchas I’ve come across in a later blog. But for now, we’ll make a basic build file.

Building our gitlab-ci.yml file

Launch Notepad, and paste the following text into it:

Our configuration file consists of a label at the top, which identifies the name of the build, the script to be executed, and uses a tag of ‘Windows’ to identify the Runner to be used.

You might be wondering why I placed :

in the build script instead of directly into the PowerShell script. The reason for this is simply to demonstrate how we can actually use PowerShell within our build script, and not just call PowerShell scripts.

  • Save the file as .gitlab-ci.yml within the repository, and return to Bash.
  • Add, commmit, and push this file to GitLab.

Results

Let’s take a look at the status of this build from GitLab. What’s particularly interesting here is that the actual command within the the script section of the build file is displayed. More about that later….

successfulbuild

So our build has reported as being successfully, and if we take a look at C:\Windows\Temp on our build server, the file is there. Our first experience with GitLab CI is complete! 🙂

helloworldfile

Coming Soon….

The next article in the series will cover some difficulties i’ve had getting to grips with GitLab CI, and how I was able to go from this :

builds

To :

success

Thanks for reading. Comments, errors and any feedback always welcome.

cheers,

Tim

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