net-core-appsettings-json-variable-replacement-in-appveyor

net-core-appsettings-json-variable-replacement-in-appveyor-1.ps1

Write-Host "Environment Variable Substitution"

$variables = gci $env:$env:APPLICATION_PREFIX* | Select-Object -Property Key, Value

$configPath = "$env:APPLICATION_PATH\$env:CONFIG_FILE"

Write-Output "Loading config file from $configPath"
$appSettings = Get-Content -Raw $configPath | ConvertFrom-Json

foreach($variable in $variables) {
    $matchString = $variable.Key.replace($env:APPLICATION_PREFIX, "")

    $matchProperties = $matchString.Split(".")

    if($matchProperties.Count -gt 1) {
        $match = $appSettings.($matchProperties[0]).psobject.properties | where { $_.Name -eq $matchProperties[1] } 
        if ($match) {
            $appSettings.($matchProperties[0]).($matchProperties[1]) = $variable.Value
        }
        else {
            Write-Output "Could not find match for $matchString"
        }
    }
    else {
        $match = $appSettings.psobject.properties | where { $_.Name -eq $matchString } 
        if ($match) {
            $appSettings.($matchString) = $variable.Value
        }
        else {
            Write-Output "Could not find match for $matchString"
        }
    }
}

$appSettings | ConvertTo-Json -depth 100 | Out-File $configPath

I was having a similar need, in my case it was more that you have a secret coming from a KeyVault and then in the appsettings the connection string where you replace that part.

In the end I wrote a library to perform variable substitution, it substitutes from any configuration source, not just environment variables.
See: https://github.com/molinch/ConfigurationSubstitutor

You just need to register it as another configuration source, this is done by calling .EnableSubstitutions() on the ConfigurationBuilder.

With your example:

• if in appsettings.json you have: "Application_Path": "%APPLICATION_PREFIX_OptimizerApp%/somepath/bla/bla/bla/"
• and you have the following environment variable: APPLICATION_PREFIX_OptimizerApp = c:/apps/
• then you should enable substitutions so:

.EnableSubstitutions("%", "%")

Finally when requesting Application_Path from the configuration you will get: c:/apps/somepath/bla/bla/bla/

How and where can I use this in my AppVeyor project?
Do I add this ps1 file to my netcore project and refer to it in the deployment tab in Appveyor?

Hi @eivindivine
Thanks for your question! If you came here from the blog post (https://mitchgollub.com/net-core-appsettings-json-variable-replacement-in-appveyor/), the directions and details are all there. You can place this code into the deploy.ps1 file at your project root that AppVeyor uses by default. This will execute the powershell script in the context of the deploy agent.

Thank you!

Thanks for your prompt reply @mitchgollub
Your blog is very thorough, but I think I may be missing som preliminary details.

The output log reports 'invalid variable reference':

And lets say I have this appsettings.json file, and I want to replace First.Second variable.

From your description, I would assume I need one environment variable for APPLICATION_PREFIX for the prefix tekst. and for the following appsettings replacements, I need to start with the prefix and then the variable values?

I'm presumably missing som basic info since this doesn't work, or I may have misunderstood your powershell script.

I got it working. I had to separate $env:$env:APPLICATION_PREFIX* into two lines (amongst a few other things).
All together, this is a much smoother solution than the parameters.xml from .net framework. Thanks for the contribution!

Hi @eivindivine,
That's great news! I was testing it out a little yesterday and had noticed my actual final version of the code is hard-coded with the application prefix

$variables = gci $env:APPID_* | Select-Object -Property Key, Value

So thats my mistake. If you'd like to share your changes, I'd be happy to update this file and credit you.

Also your assumptions on the variable replacement configuration are correct, but you probably knew that already.

Thanks!

@mitchgollub I wasn't able to send direct messages so I had to create it as a page:
https://gist.github.com/eivindivine/83cbfbf2efb97575ec7c1268459a05a0/041585263d9c428a4d8506510626c875948abc58