如何根据先前执行的资源有条件地执行 Powershell DSC 中的资源？

Question

假设我有两个这样的块：

Configuration TestConfig
{
    Node ('localhost') {
        File foo {
            DestinationPath = 'C:\foo.txt'
            Contents = 'Bar'
        }
        Script dothing {
            SetScript = {'Baz' | set-content C:\foo.txt}
            TestScript = {return $false}
            GetScript = {
                return @{
                    GetScript = ''
                    SetScript = ''
                    TestScript = ''
                    Credential = $Credential
                    Result = (Invoke-Expression -Command $TestScript)
                }
            }
            DependsOn = '[File]foo'
        }
    }
}

我构建了一个执行类似操作的测试，但似乎无论 File 资源的测试输出如何，Service 资源都会被执行 - 也就是说，如果它实际上对文件做了任何事情。

VERBOSE: [MACHINENAME]: LCM:  [ Start  Set      ]
VERBOSE: [MACHINENAME]: LCM:  [ Start  Resource ]  [[File]foo]
VERBOSE: [MACHINENAME]: LCM:  [ Start  Test     ]  [[File]foo]
VERBOSE: [MACHINENAME]:                            [[File]foo] The destination object was found and no action is required.
VERBOSE: [MACHINENAME]: LCM:  [ End    Test     ]  [[File]foo]  in 0.0040 seconds.
VERBOSE: [MACHINENAME]: LCM:  [ Skip   Set      ]  [[File]foo]
VERBOSE: [MACHINENAME]: LCM:  [ End    Resource ]  [[File]foo]
VERBOSE: [MACHINENAME]: LCM:  [ Start  Resource ]  [[Script]dothing]
VERBOSE: [MACHINENAME]: LCM:  [ Start  Test     ]  [[Script]dothing]
VERBOSE: [MACHINENAME]: LCM:  [ End    Test     ]  [[Script]dothing]  in 0.0050 seconds.
VERBOSE: [MACHINENAME]: LCM:  [ Start  Set      ]  [[Script]dothing]
VERBOSE: [MACHINENAME]: LCM:  [ End    Set      ]  [[Script]dothing]  in 0.0060 seconds.
VERBOSE: [MACHINENAME]: LCM:  [ End    Resource ]  [[Script]dothing]
VERBOSE: [MACHINENAME]: LCM:  [ End    Set      ]
VERBOSE: [MACHINENAME]: LCM:  [ End    Set      ]    in  0.0390 seconds.

抛开人为的例子不谈，我怎样才能让脚本资源只有在文件资源实际执行某些操作时才执行？

我的用例是检查远程位置的文件是否已更改，如果是，请将其复制到本地计算机，然后重新启动服务。如果文件没有更改，我显然不想重新启动服务，但我看不到一个好的幂等方法，因为正在使用哈希测试文件 - 我必须拥有我的服务重新启动步骤执行相同的文件哈希检查。

Answer 1

我认为 DSC 中没有任何原生内置功能可以让一个资源检测“Set-TargetResource”函数是否在同一配置运行中针对不同资源实际执行。

但是，以下脚本资源可以满足您的需求，但它们使用全局脚本级变量进行通信，因此如果您在单个 DSC 中配置多个服务，它们就会中断。 ConfigureService 脚本资源更新本地配置文件并设置一个标志，RestartService 资源读取该标志以检查是否进行了更改。它有点脏，但它可以工作。

Script ConfigureService {
    GetScript  = { return $null; }
    TestScript = {
        # compare remote and local file contents and return 
        # $true if they match, or $false if they're different
        $source = "D:\temp\dsctest\source.txt";
        $target = "D:\temp\dsctest\target.txt";
        $isMatch = [System.IO.File]::ReadAllText($target) -eq [System.IO.File]::ReadAllText($source);
        # set a flag for the RestartService resource to read
        $script:serviceChanged = -not $isMatch;
        write-verbose "isMatch = $isMatch";
        return $isMatch;
    }
    SetScript  = {
        # overwrite the local file
        $source = "D:\temp\dsctest\source.txt";
        $target = "D:\temp\dsctest\target.txt";
        $content = [System.IO.File]::ReadAllText($source);
        write-verbose "overwriting config";
        [System.IO.File]::WriteAllText($target, $content);
    }
}

Script RestartService {
    DependsOn  = "[Script]ConfigureService"
    GetScript  = { return $null; }
    TestScript = {
        write-verbose "serviceChanged = $($script:serviceChanged)";
        return -not $script:serviceChanged;
    }
    SetScript  = {
        # restart the service
        write-verbose "restarting service";
    }
}

或者，只需将其全部整合到一个资源中。如果您想将其重新用于多个服务，您可以将其移动到成熟的 ServiceConfiguration 自定义资源中。

Script ConfigureService {
    GetScript  = { return $null; }
    TestScript = {
        # compare remote and local file contents and return 
        # $true if they match, or $false if they're different
        $source = "D:\temp\dsctest\source.txt";
        $target = "D:\temp\dsctest\target.txt";
        $isMatch = [System.IO.File]::ReadAllText($target) -eq [System.IO.File]::ReadAllText($source);
        write-verbose "isMatch = $isMatch";
        return $isMatch;
    }
    SetScript  = {
        # overwrite the local file
        $source = "D:\temp\dsctest\source.txt";
        $target = "D:\temp\dsctest\target.txt";
        $content = [System.IO.File]::ReadAllText($source);
        write-verbose "overwriting config";
        [System.IO.File]::WriteAllText($target, $content);
        # restart the service
        write-verbose "restarting service";
    }
}