Earlier this week I received a question from a customer who was interested in creating a custom ESXi VIB that could execute a specific script within the payload as part of the installation and only running it once. This was a fairly common request that I have seen in the past and as far as I knew, this type of behavior was not possible. What was unique about this particular custom inquiry was that they mentioned they found some references on this being possible. Being the curious person I am, I decided to take another look and reach out to a few folks in Engineering.
After speaking with one of the Engineers familiar with our VIB specification, to my surprise I learned that this type of behavior was actually indeed possible but was not very well documented externally. The typical use case for this is usually to apply certain configurations which are not exposed through the traditional ESXi interfaces like the vSphere API/CLI which includes Host Profiles. One example that comes to mind is being able to deploy a VIB across several hundred ESXi hosts that could configure a specific ESXi Advanced Setting which might be marked hidden. Another example would be updating a configuration file like /etc/vmware/config or running a series of ESXi Shell commands which can not available in the vSphere API and require the use of SSH and the ESXi Shell. There are many other examples, but this should give you an idea of some of the common use cases that I have heard from customers.
Here is what is required to execute a specific script as part of the VIB installation:
- Created an "init" script which needs to be stored under /etc/init.d as part of your VIB payload (e.g. /etc/init.d/lamw-special-vib)
- You must ensure that the "live-install-allowed" param is set to true in your VIB's descriptor.xml file (this assumes the changes can be applied without requiring reboot to take affect)
- The init script will need to parse special keywords passed as command-line arguments
Here is a table showing the pair of special keywords that are passed to the init script as command-line arguments during a VIB install, upgrade or remove:
| Arg1 | Arg2 | VIB Operation |
|---|---|---|
| start | install | VIB install |
| start | upgrade | VIB upgrade |
| stop | remove | VIB removal |
It is up to creator of the init script to handle the different VIB operations by parsing the command-line arguments which would then determine the operations that would get executed within the script. This not only allows you to control the commands that are executed during an installation of a VIB but it also allows you specify the commands to run upon the removal of a VIB which is quite handy for properly cleaning up an uninstall. In addition, since these special keywords are not passed as part of the ESXi boot up process, the commands within the script will not execute and ensures it only runs once during the install.
Here is very simple shell script (you could also do this in Python as well) which demonstrates how to handle the three different types of VIB operations and then uses the "logger" utility to write some output to syslog:
#!/bin/sh
ARG1=$1
ARG2=$2
if [[ "${ARG1}" == "start" ]] && [[ "${ARG2}" == "install" ]]; then
# commands to run go here #
/bin/logger "William's custom script ran on start-install"
elif [[ "${ARG1}" == "start" ]] && [[ "${ARG2}" == "upgrade" ]]; then
/bin/logger "William's custom script ran on start-upgrade"
# commands to run go here #
elif [[ "${ARG1}" == "stop" ]] && [[ "${ARG2}" == "remove" ]]; then
/bin/logger "William's custom script ran on stop-remove"
# commands to run go here #
fi
As you can see, this allows you to perform a variety of tasks through the use of a custom ESXi VIB which is a great way to be able to roll out a set of changes that may not be possible using either the vSphere API or Host Profiles for example. Best of all, this solution does not require the use of SSH which is great since many customers already disable this by default.
For more information on creating a custom VIB, be sure to check out my blog post here and you can even use this Docker image I created for building custom ESXi VIBs.
