This discussion started as a support thread here:

http://help.octopusdeploy.com/discussions/questions/2571-web-package-based-parameters

Let's say I have an App.config for a Windows Service that looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <!-- snip -->
  <system.net>
    <mailSettings>
      <smtp from="user@localdomain.org">
        <network host="smtp.local" />
      </smtp>
    </mailSettings>
  </system.net>
  <!-- snip -->
</configuration>

With the built-in transformations (appSettings and connectionStrings) I cannot replace the SMTP server host.

For web projects in the past, I've used msdeploy (or web deploy) package parameters to do this transformation from environment to environment.

The idea is you create a parameters.xml file locally to your project, and then each environment has a corresponding setParameters.xml file that defines the values for the defined parameters.

So, a parameters.xml file would look like this:

<parameters>
  <parameter name="Smtp Server" description="Address to server that provides smtp" defaultValue="smtp.dev" tags="" >
    <parameterEntry kind="XmlFile" scope="\\Service.exe.config$" match="/configuration/system.net/mailSettings/smtp/network/@host" />
  </parameter>
</parameters>

And instead of the setParameters.xml file typically used, we could just use the Octopus Variables functionality. For the example above, you'd just need a Variable for "Smtp Server".

I've put something together that works for me for now, but would prefer if something like this could be built in.

Here's what I've got for now:

A custom Powershell Script (imported into Octopus Deploy Lirary as a Script module):

[Reflection.Assembly]::LoadWithPartialName("System.Xml") | Out-Null
[Reflection.Assembly]::LoadWithPartialName("System.Xml.XPath") | Out-Null
[Reflection.Assembly]::LoadWithPartialName("System.Xml.Linq") | Out-Null

function Sync-DeployParameters { param($variables, $pathToParameters = "parameters.xml", $fileFilters = @("*.config", "*.xml"))
  $pathToParameters = (Resolve-Path($pathToParameters)).Path

  if(!(Test-Path $pathToParameters)) {
    throw "Could not find parameters file: $pathToParameters"
  }

  $parametersXml = [System.Xml.Linq.XDocument]::Load($pathToParameters)

  $parameters = $parametersXml.Descendants('parameter')

  foreach($parameter in $parameters) {

    $key = $parameter.Attribute('name').Value

    Write-Output "'$key'"

    if($variables.ContainsKey($key) -eq $false) {
      Write-Output "No matching variable. Skipping."
      continue
    }

    $parameterEntry = $parameter.Element('parameterEntry')

    $kind = $parameterEntry.Attribute('kind').Value

    if($kind -ne 'XmlFile') {
      Write-Output "parameterEntry is not of kind XmlFile. Skipping."
      continue
    }

    $scope = $parameterEntry.Attribute('scope').Value
    $xpathMatch = $parameterEntry.Attribute('match').Value

    $pathsInScope = Get-PathsToConfigs $scope @($fileFilters)

    if(!($pathsInScope)) {
      Write-Output "Could not find scope: $scope"
    }

    foreach($pathInScope in $pathsInScope) {
      if((Test-Path $pathInScope) -eq $false) {
        continue
      }

      Set-XPathValue $pathInScope $xpathMatch $variables[$key]
    }
  }
}

function Get-PathsToConfigs { param([string]$scope, [string[]]$fileFilters)
  $relativelyScoped = "\.$scope"
  return Get-ChildItem . -Recurse -Include $fileFilters | Where-Object { (Resolve-Path($_.FullName) -Relative) -match $relativelyScoped } | %{ $_.FullName }
}

function Set-XPathValue { param([string]$pathToFile, [string]$xpath, [string]$value)
  Write-Output "$pathToFile - $xpath='$value'"

  $document = New-Object System.Xml.XmlDocument
  $document.PreserveWhitespace = $true
  $document.Load($pathToFile)

  $navigator = $document.CreateNavigator()

  $manager = New-Object System.Xml.XmlNamespaceManager($navigator.NameTable)

  foreach ($nav in $navigator.Select($xpath, $manager))
  {
    $nav.SetValue($value)
  }

  $document.Save($pathToFile)
}

Export-ModuleMember -Function Sync-DeployParameters

And then inside my process (Nuget package) that deploys the Windows Service, I have Custom Powershell scripts turned on that execute as a 'Deployment script':

Sync-DeployParameters $OctopusParameters

This is incomplete; I haven't tested it much. One obvious missing feature is to use the defaultValue specified in the parameters.xml file, but that should be easy to do.

Is it possible something like this could get built into Octopus Deploy? Or did I miss the whole point and there's an easier way to do this? I've seen the substitute in files feature, but I don't like it as much because I have to keep templates around of my config files.