Question

我的脚本下面有以下代码片段，它使用WebRequest来ping一个Web / app服务器列表，我根据服务器列表中列出的好/坏服务器的顺序得到随机结果。

例如，如果列表中首先列出了错误的服务器（我收回404或503的代码），那么我的脚本似乎准确报告。但是，如果首先列出好的服务器（返回状态=“OK”），那么我的结果就不准确了。

这是我的代码段：

$ServerList = gc "$pwd\servers\test_servers.lst"
ForEach ($_ in $ServerList)
{   
# Ping web server test
$url = "http://$_.domain.net/logon"
Write-Host "Pinging web address for server: $url ..."
$request = [System.Net.WebRequest]::Create($url)
$response = $request.GetResponse()
If ($response.StatusCode -eq "OK") 
{
    #$True
    Write-Host "Web Ping on $_ Succeeded."
} 
Else 
{
    #$False
    Write-Host "Web Ping on $_ FAILED!!!"
}       
}

以下是示例服务器列表：

server1 (reports back a 404)
server2 (reports back a 503)
server3 (gets a status = "OK")

运行脚本时，这是“准确的”cmd输出：

C:\TFS\Sandbox>powershell ./temp.ps1

Pinging web address for server: http://server1.domain.net/wfc/logon ...
Exception calling "GetResponse" with "0" argument(s): "The remote server return
ed an error: (404) Not Found."
At C:\TFS\Sandbox\temp.ps1:8 char:34
+     $response = $request.GetResponse <<<< ()
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException
Web Ping on server1 FAILED!!!

Pinging web address for server: http://server2.domain.net/wfc/logon ...
Exception calling "GetResponse" with "0" argument(s): "The remote server return
ed an error: (503) Server Unavailable."
At C:\TFS\Sandbox\temp.ps1:8 char:34
+     $response = $request.GetResponse <<<< ()
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException
Web Ping on server2 FAILED!!!

Pinging web address for server: http://server3.domain.net/wfc/logon ...
Web Ping on server3 Succeeded.

现在，当我重新订购首先列出好服务器的服务器列表时，就像这样：

server3 (gets a status = "OK")    
server1 (reports back a 404)
server2 (reports back a 503)

我得到的结果不准确，服务器1和服务器2报告为OK：

Pinging web address for server: http://server3.domain.net/wfc/logon ...
Web Ping on server3 Succeeded.

Pinging web address for server: http://server1.domain.net/wfc/logon ...
Exception calling "GetResponse" with "0" argument(s): "The remote server return
ed an error: (404) Not Found."
At C:\TFS\Sandbox\temp.ps1:8 char:34
+     $response = $request.GetResponse <<<< ()
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException
Web Ping on server1 Succeeded.

Pinging web address for server: http://server2.domain.net/wfc/logon ...
Exception calling "GetResponse" with "0" argument(s): "The remote server return
ed an error: (503) Server Unavailable."
At C:\TFS\Sandbox\temp.ps1:8 char:34
+     $response = $request.GetResponse <<<< ()
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException
Web Ping on server2 Succeeded.

为什么我根据服务器的列表方式得到混合结果？

提前致谢！

Answer 1

您可能需要关闭连接：

$response.Close()

http://msdn.microsoft.com/en-us/library/system.net.webresponse.close(v=vs.90).aspx

我会这样写：

foreach ($server in $ServerList) {
    try {
        $url = "http://${server}.domain.net/logon"
        Write-Host "Pinging web address for server: $url ..."
        $request = [System.Net.WebRequest]::Create($url)
        $response = $request.GetResponse()
        Write-Host "Web Ping on $server Succeeded."   
    } catch {
        Write-Host ("Web Ping on $server FAILED!!! The error was '{0}'." -f $_)
    } finally {
        if ($response) {
            $response.Close()
            Remove-Variable response
        }
    }
}

Answer 2

这是因为WebRequest引发了不成功尝试的异常，而$response在您获得503，404等情况下并未真正设置。你确实获得了成功，响应被设置为响应（状态代码正常），但是如果下一个服务器引发404，那么响应仍然是OK状态，因为WebRequest只引发异常并且没有不给$ response分配任何东西。您可能希望trap（或try catch）异常并在那里处理成功或失败，或者在循环的每次迭代中将$response设置为null：

foreach($server in $serverlist){
$response=$null

...

另外，不要使用$_作为迭代变量，它是自动变量，并且不是在这里使用它的好形式。

请注意，您所写的内容也可能会耗尽系统资源（它暂停一次），因此请妥善处理相应的响应。 $response = $null可能就足够了，但您可能仍需要在循环结束时正确关闭响应。

使用PowerShell进行随机WebRequest结果

2 个答案: