March 2010 - The Practical Administrator

Being, first and foremost, lazy and getting my paychecks for being a system administrator, I felt that the amount of work involved in loading ESXi 4.0 on my blades was entirely too much. I have well over 100 blades, each one needing to have vSphere loaded onto it, configured, and added to vCenter. Even using the directions scattered across the internet about reducing the amount of effort involved in loading vSphere was too much for me.

Others have documented how to PXE boot ESXi elsewhere on the internet, however I wasn’t interested in having a “stateless” install…I merely wanted to automate installing ESXi to the local hard drive. My blades have a single hard drive, a single generation one SSD or two SAS drives in a RAID 1 depending on the vendor, and I simply want the installer to always install to that drive without bothering me. Loading from the “remote media” functionality of the DRAC/iLO for the blades takes forever, so I wanted to be able to install using PXE and push the media over that medium.

So, having been a developer for several years I decided to dive further into the the install process than others had detailed. Turns out that eliminating all input from an administrator to load the operating system was pretty simple.

The end result is that I am able to power on a blade, hit F12 to have it PXE boot and walk away. Some time later, we can use PowerShell and the PowerCLI to find the hosts (they will be somewhere in the DHCP scope of the provisioning LAN), give them a permanent IP and hostname, then configure them and add them to vCenter. By using PXE and the interactionless (yes, I did make up that word) install, I cut the time to load ESXi from about 45 minutes (using the remote media function takes FOREVER!) to less than 10.

Read moreESXi 4.0 autoinstall

While scanning the PowerShell forums this evening I ran accross this question. Cruisader03 had already answered the question. The solution.. just…. looked too complicated. After three years of using PowerShell everyday as my primary means of administration… I offer this simple mantra.

If it looks complex your doing it wrong!… And you’re the second person to read it.

I just made that up, but I like it! Seriously though, this is something I’ve started to notice in my own code. I believe it is an interesting side effect of the Admin Development Model.

We cut and paste, one line at a time. Until we get it to work. By the time we finish a script we know that code not as a script, but as a series of lines. (Pay attention, I bet you still read it like a series of one liners). In that context it looks fine, but wait 24hr’s and look again… not the same is it. Now that you’re looking at a finished script. You will start to find all sorts of inefficiencies and poor grammar usage. So you polish it up a little… rinse and repeat 100 times, and post to PoshCode! So goes the Admin Development Model. With that in mind I offer this simple snip it, more a refactor of Cruisader03 post than a solution.

<span style="color: #ff4500;">$name</span> <span style="color: #a9a9a9;">=</span> <span style="color: #8b0000;">'.'</span>            

<span style="color: #0000ff;">Get-WmiObject</span> <span style="color: #8a2be2;">Win32_NetworkLoginProfile</span> <span style="color: #000080;">-ComputerName</span> <span style="color: #ff4500;">$name</span><span style="color: #a9a9a9;">|</span>
    <span style="color: #006400;">#Filter out any non valid DTG</span>
    <span style="color: #0000ff;">Where-Object</span> <span style="color: #000000;">{</span><span style="color: #ff4500;">$_</span><span style="color: #a9a9a9;">.</span><span style="color: #000000;">LastLogon</span> <span style="color: #a9a9a9;">-match</span> <span style="color: #8b0000;">"(?&lt;dtg&gt;d{14}.d{6}S)(?&lt;offset&gt;d+)$"</span><span style="color: #000000;">}</span><span style="color: #a9a9a9;">|</span>
    <span style="color: #006400;">#Foreach valid entry find the last logon dtg</span>
    <span style="color: #0000ff;">ForEach-Object</span> <span style="color: #000000;">{</span>
        <span style="color: #006400;"># Win32_NetworkLoginProfile formats the utc offset in seconds this</span>
        <span style="color: #006400;"># Breaks the DateTime parser.  We reformat the string converting</span>
        <span style="color: #006400;"># the offset back to hours</span>
        <span style="color: #ff4500;">$CorrectedDTG</span> <span style="color: #a9a9a9;">=</span> <span style="color: #8b0000;">"{0}{1:00}"</span> <span style="color: #a9a9a9;">-f</span> <span style="color: #ff4500;">$matches</span><span style="color: #a9a9a9;">.</span><span style="color: #000000;">dtg</span><span style="color: #a9a9a9;">,</span> <span style="color: #000000;">(</span><span style="color: #ff4500;">$matches</span><span style="color: #a9a9a9;">.</span><span style="color: #000000;">offset</span><span style="color: #a9a9a9;">/</span><span style="color: #800080;">60</span><span style="color: #000000;">)</span>            

        <span style="color: #0000ff;">New-Object</span> <span style="color: #8a2be2;">PSObject</span> <span style="color: #000080;">-Property</span> <span style="color: #000000;">@{</span>
            <span style="color: #000000;">Name</span><span style="color: #a9a9a9;">=</span><span style="color: #ff4500;">$_</span><span style="color: #a9a9a9;">.</span><span style="color: #000000;">Name</span>
            <span style="color: #000000;">LogonTime</span><span style="color: #a9a9a9;">=</span><span style="color: #008080;">[datetime]</span><span style="color: #a9a9a9;">::</span><span style="color: #000000;">ParseExact</span><span style="color: #000000;">(</span><span style="color: #ff4500;">$CorrectedDTG</span><span style="color: #a9a9a9;">,</span> <span style="color: #8b0000;">"yyyyMMddhhmmss.ffffffzz"</span><span style="color: #a9a9a9;">,</span> <span style="color: #ff4500;">$null</span><span style="color: #000000;">)</span>
        <span style="color: #000000;">}</span>
    <span style="color: #000000;">}</span> <span style="color: #a9a9a9;">|</span>
    <span style="color: #0000ff;">Sort-Object</span> <span style="color: #000080;">-Descending</span> <span style="color: #8a2be2;">LogonTime</span> <span style="color: #a9a9a9;">|</span>
    <span style="color: #0000ff;">Select-Object</span> <span style="color: #000080;">-First</span> <span style="color: #800080;">1</span>

$name = '.'

Get-WmiObject Win32_NetworkLoginProfile -ComputerName $name|

#Filter out any non valid DTG

Where-Object {$_.LastLogon -match "(?<dtg>d{14}.d{6}S)(?<offset>d+)$"}|

#Foreach valid entry find the last logon dtg

ForEach-Object {

# Win32_NetworkLoginProfile formats the utc offset in seconds this

# Breaks the DateTime parser. We reformat the string converting

# the offset back to hours

$CorrectedDTG = "{0}{1:00}" -f $matches.dtg, ($matches.offset/60)

New-Object PSObject -Property @{

Name=$_.Name

LogonTime=[datetime]::ParseExact($CorrectedDTG, "yyyyMMddhhmmss.ffffffzz", $null)

}

} |

Sort-Object -Descending LogonTime |

Select-Object -First 1

~Glenn