Accessing network configuration of ESX servers

One of my recent tasks involved reading and processing networking configurations from an ESX server. As a concrete example, consider that you want to list all the VLAN tags currently used. There are multiple ways to do that. The first choice is the handy console program "esxcfg-vswitch -l", which prints information about all vswitches including portgroups with their VLAN tags . This works nicely, but needs some parser/regular expression matching to extract the required information.

Another tool is"esxcfg-info", which prints lots of information about the ESX server. By default, that prints the whole configuration as a (very long) formatted text. Reading through that is possible, but not very pleasant. So the first step is to reduce the amount of data by using the "-n" option, which results in printing only the network part (other options are e.g. "-s" for storage related information. "esxcfg-info -h" prints a list of all available options). But even "esxcfg-info -n" still prints a vast amount of information compared with "esxcfg-vswitch -l", so why even consider using that? The answer is the "-F" option that can change the output to either XML or Perl. Unfortunately, the XML output is currently broken (see this thread for details), so that leaves us with the Perl output format. "esxcfg-info -n -F perl" prints the same information as "esxcfg-info -n", but as one big Perl datastructure. To use it, simply evaluate the result within your Perl script and then navigate through the big nested hashmap. No more parsing needed!

Granted, if the goal would have been really to just list all the VLAN tags, parsing the output of "esxcfg-vswitch -l" is still simpler than navigating though the data. However, if you need to answer more complex questions about the network, with a single line of Perl you get a pre-populated, nice datastructure that contains all there is to know.

There are of course more options (aren't there always?). Leaving the crazy idea of parsing the HTML output of the web interface aside, there are SDKs provided by VMware that allow to access the same information remotely. More about this next time...