Start-DockerJob Part 2

… Continuing from

Part 1 - sketching out the idea.

Arguments/Parameters

Being able to run arbitrary powershell will only get you so far if you can’t provide any parameters. I modified the StartDockerJobCommand class to add a ArgumentList parameter as per Start-Job.

[Parameter(Position = 1)]
public object[]? ArgumentList { get; set; }

Then within the ProcessRecord method I added a little bit of code to serialize this to CLI XML and Base64 encode it before adding it to the arguments I pass to the docker process ¹.

if (ArgumentList != null && ArgumentList.Length != 0)
{
    dockerRunArguments.Add("-EncodedArguments");
    var serializedArguments = PSSerializer.Serialize(ArgumentList);
    dockerRunArguments.Add(Convert.ToBase64String(Encoding.Unicode.GetBytes(serializedArguments)));
}

I’ve also made sure that I’m specifying that the -inputFormat is XML, and whilst I’m on, switched to using -EncodedCommand rather than -Command.

Parameters may be accessed using the $args array or by specifying a param block as part of the ScriptBlock. I’m not sure how one would go about using the using scope modifier for this, so we’ll park that for now.

$api = 'https://catfact.ninja/fact'                                        
Start-DockerJob -ScriptBlock {Invoke-Restmethod -Uri $args[0]} -ArgumentList $api  -DockerImage mcr.microsoft.com/powershell:preview-mariner-2.0-arm64

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
6      DockerJob                       Running       False           localhost

Get-Job | Receive-Job
fact                                                                        length
----                                                                        ------
In multi-cat households, cats of the opposite sex usually get along better.     75

Get-Job | Remove-Job

Start-DockerJob -ScriptBlock {param($api) invoke-restmethod -uri $api} -ArgumentList $api  -DockerImage mcr.microsoft.com/powershell:preview-mariner-2.0-arm64

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
7      DockerJob                       Running       False           localhost

Get-Job | Receive-Job
fact
----
There is a species of cat smaller than the average housecat. It is native to Africa and it is the Black-footed cat (Felis nigripes). Its top weight is 5.5 p…

Get-Job Properties

The Get-Job output was not showing the command used, even though I was generating it by concatenating the dockerRunArguments list with a space character and passing into the JobInvocationInfo specification. This was because I wasn’t calling the appropriate base constructor on my StartDockerJobCommand constructor. Easily remedied.

public DockerJob(string jobName, List<string> arguments, string command) : base(command, jobName)

The PSJobTypeName property was even easier and just needed setting in the constructor, referencing a private const variable already defined.

PSJobTypeName = DockerJobName;

Start-DockerJob -ScriptBlock {'test'} -DockerImage mcr.microsoft.com/powershell:preview-mariner-2.0-arm64

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
1      DockerJob       DockerJob       Running       False           localhost            run --name c4fe0526-9298…

Similarly, I’d missed setting the Name property of the JobInvocationInfo soecification object. This was set in the sample, so was an omission on my part in my first stab.

To Be Continued…

Part 3 - Adding contexts, implementing job operations.

Actually, it’s the arguments to the powershell interpreter within the container that are being passed as part of the arguments passed to the docker process but let’s not worry about that. ↩︎