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PowerCLI - MethodException Error when using ESXCLI on Multiple Hosts

·637 words·3 mins

One of my favorite capabilities in PowerCLI is the ability to run ESXCLI commands. All without having to deal with the headache of enabling SSH on all your hosts and digging up their root passwords from (hopefully) your password manager. PowerShell also gives you the ability to implicitly run commands against all objects in an array by requesting the object method directly. When you combine these two features, it gives you the power to easily run ESXCLI commands on all of your hosts, like this:

PS > # Creates ESXCLI interfaces for all ESXi hosts in the domain
PS > $esxclis = Get-VMHost | Get-EsxCli -V2

PS > # List all DNS servers configured on each host
PS > $esxclis.network.ip.dns.server.list.Invoke()

DNSServers
----------
{10.0.0.1}
{10.0.0.1}
{10.0.0.1}
{10.0.0.1}

PS > # Ping the DNS server from each host and show how many packets were lost
PS > $esxclis.network.diag.ping.Invoke(@{"host"="10.0.0.1"}).Summary.PacketLost

0
0
0
0

However, if you use this capability as much as I do, you may have run into an error message like this before:

PS > # Attempts to show the hostnames for every ESXi host
PS > $esxclis.system.hostname.get.Invoke()
MethodException: Cannot find an overload for "Get" and the argument count: "0".

You might think that there are just some ESXCLI commands that PowerCLI doesn’t allow you to run on multiple ESXi hosts at the same time. However, the error is simply because $esxclis is a PowerShell array that contains ESXCLI interfaces. Arrays already have a Get method defined for them, which conflicts with the get command in ESXCLI. When you call get directly against $esxclis, PowerShell assumes you meant the Get method for the array itself, not the get command for the underlying ESXCLI interfaces.

PS > $esxclis.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

PS > $esxclis.Get

OverloadDefinitions
-------------------
System.Object Get(int )

The Get method for a PowerShell array expects an integer parameter for which element to return from the array. So, $esxclis.Get(0) is equivalent to $esxclis[0]. We receive the MethodException error simply because we didn’t provide an integer when attempting to use the get command. Of course, that isn’t our real issue. The real issue is that PowerShell is using the array’s Get method in the first place.

This issue will also happen for anything else that conflicts with the name of an array method, such as set and address. This also means that the error doesn’t occur when using ESXCLI against a single host.

PS > # Attempts to set NTP server for all hosts
PS > $esxclis.system.ntp.set.Invoke(@{"server"="time.nist.gov"})
MethodException: Cannot find an overload for "Set" and the argument count: "1".

PS > # Attempts to list IPv4 addresses of VMkernel interfaces for all hosts
PS > $esxclis.network.ip.interface.ipv4.address.list.Invoke()
InvalidOperation: You cannot call a method on a null-valued expression.


PS > # Lists IPv4 addresses of VMkernel interfaces for a single host
PS > $singleCli = Get-VMHost -Name "esxi-1.sddc.lab" | Get-EsxCli -V2
PS C:\Users\berna> $singleCli.network.ip.interface.ipv4.address.list.Invoke()

AddressType   : STATIC
DHCPDNS       : false
Gateway       : 10.0.0.1
IPv4Address   : 10.0.0.11
IPv4Broadcast : 10.0.0.255
IPv4Netmask   : 255.255.255.0
Name          : vmk0

To resolve this issue, all we need to do is pipe $esxclis into a ForEach-Object command and run our commands from within there. In the example, % is the alias for ForEach-Object and $_ represents each individual ESXCLI interface within the array.

PS > # Shows hostnames for all ESXi hosts in the domain
PS > $esxclis.system.hostname | % { $_.get.Invoke() }

DomainName FullyQualifiedDomainName HostName
---------- ------------------------ --------
sddc.lab   esxi-1.sddc.lab       esxi-1
sddc.lab   esxi-2.sddc.lab       esxi-2
sddc.lab   esxi-3.sddc.lab       esxi-3
sddc.lab   esxi-4.sddc.lab       esxi-4

Unfortunately, there isn’t a way to force PowerShell to use that get command without using a for loop of some kind. But at the very least, this method doesn’t add too much boilerplate code and it allows us to keep the full ESXCLI command in one line.