Cattle vs Pets

Cattle and Pets are ways to classify how you think about a compute unit that is involved in providing a service.  Typically the unit would be a server ( metal or virtual ) but can also be a container ( e.g Docker ) that is running on a server.  The compute units classification will determine how you treat it.


Can be destroyed and replaced at any time without the service failing.  It’s Cattle


Indispensable; destroying and replacing will cause the overall service to fail. It’s a Pet.



EXCHANGE01 is ACME Corporations single server providing email to the entire company. If it goes down, email service is lost.   EXCHANGE01 is a Pet

The cluster compromising virtual servers WWW001 through to  WWW100 , provides ACME Corporation website to the world.  Any server in that cluster can be destroyed and replaced without ACME Corporations website failing.  Therefore these servers are Cattle




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Symbol not found: __PyCodeInfo_GetIncrementalDecoder

After upgrading the version of Python on my Mac, I immediately got the above error when attempting to run a Python script. You can quickly test by typing

import io

and you’ll get the error

Quick digging around on Google revealed what was happening. When a new version of Python is installed, you may need to tell bash to reset the ‘cached’ location to Python. There’s two ways of achieving that

1) Log out and then log back in
2) At the terminal prompt, type

hash -r python
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El Capitan download & Squid proxy

Last night I left my Mac downloading the update to El Capitan overnight so it would be ready for me to install following the morning.

I was greeted by a rather generic message saying that the download had failed. A bit of digging showed 2.15Gb had been downloaded before the failure. Maybe it was network disruption; I live in the countryside and it’s not unknown for the VDSL to drop out. Nothing to worry about, downloads resume from where they left off , so I tried again.

It failed again.

And again.

Activated debug mode for AppStore , cleared cookies, reset application and set the Debug level to 2.


And it failed again at the same point.

Browse of the App Store log file showed NSURLErrorDomain – 1005

Which was helpful in the same way that bricks are to aerodynamics.

Between the internet and my home network is a Squid proxy. I decided to eliminate that as a possible cause.

Several mouse clicks later and El Capitan is downloading without any errors.

Right now I don’t have time to investigate why Squid caused a failure ( max size of cache objects? ) but if others are in a similar situation , switch off the web proxy on your Mac.

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Zero stop day is fast approaching

Busy day today securely wiping and then installing operating systems onto 1 x MacBook Air, 2 x Dell Workstations and a Lenovo W500.

All going back to Novell / MicroFocus tomorrow.

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Time for a change

After almost 8 years, I am moving on from Novell. I handed in my resignation last Friday 24th April and will be leaving towards the end of May.

Whilst at Novell I have met and worked with great people on some fantastic products. I wish them all the best in the future.

For me, I’m onto new adventures with a U.K based security company — Sophos.


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Thou shalt not install infidel software on the holy domain controller

Unless you really really have to.

In my case I needed to install VMware vsphere 5.5 client onto my lab domain controller. VMware had other ideas and clearly had decided that they needed to save my soul and prevented me from doing so.

Happily, you can override Bishop VMware by using a tool of the devil – a command line switch /VSKIP_OS_CHECKS=”1″ with the VMware client installer. Here’s an example

VMware-viclient-all-5.5.0-1281650.exe /VSKIP_OS_CHECKS="1"

Apostates rejoice !

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Rename Active Domain Controller


You must be a member of the Domain Admins group.


Reboot will be required


To rename a DC with the name from MY-SERVER in the PMLAB.LOCAL domain to DC-SERVER follow the next steps:

1. Open Command Prompt and type:


This command will update the service principal name (SPN) attributes in Active Directory for this computer account, and register DNS resource records for the new computer name. The SPN value of the computer account must be replicated to all DCs for the domain, and the DNS resource records for the new computer name must be distributed to all the authoritative DNS servers for the domain name. If the updates and registrations have not occurred prior to removing the old computer name, then some clients may be unable to locate this computer using the new or old name. Therefore, it’s very important to wait till the Active Directory replication finishes a replication cycle. You can check that by using tools such as REPADMIN and REPLMON.

You can verify the new name was indeed added to the computer object by viewing it through ADSIEDIT.MSC (which, for Windows Server 2008, is installed by default). Navigate to the computer object and right-click it. Select Properties:

Scroll down in the list of available attributes till you reach the attribute called msDS-AdditionalDnsHostName.

2. Ensure the computer account updates and DNS registrations are completed, then type:


Again, you can inspect the change with ADSIEDIT.MSC. Scroll down in the list of available attributes for the computer object (notice how the server now appears with the new name) till you reach the attribute called msDS-AdditionalDnsHostName.

Notice that the old name should appear in the attribute’s properties.

3. Restart the computer.

4. From the command prompt, type:


5. Make sure that the changes have successfully been replicated to all the DCs.


Adapted from Perti IT Knowledge base
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