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How to run PowerShell cmdlets on remote servers
The Invoke-Command and New-PSSession PowerShell cmdlets can make it easier for admins to manage a number of remote servers.
PowerShell is a powerful command-line environment that can be used to manage and maintain Windows. While it is easy to think of PowerShell as a local management tool, it can also be used to manage remote servers. In fact, admins can create PowerShell scripts that perform management tasks against large numbers of servers. And the Invoke-Command and New-PSSession commands are two ways to execute PowerShell cmdlets on remote systems.
Invoke-Command
If you only need to run a single cmdlet (or a series of piped cmdlets) against one or more remote servers, the easiest way to do so is to use the Invoke-Command cmdlet. Microsoft's documentation for this cmdlet lists an overwhelming number of parameters and syntax variations, leading to the Invoke-Command cmdlet's reputation for being excessively complex. Even so, using Invoke-Command to run a cmdlet on a remote system is surprisingly easy.
For basic remote cmdlet execution, you only need to supply the name of the remote computer and the block of code that you want to execute. Suppose you wanted to run the Get-VM cmdlet on a remote server named Production1. You could do so by using this command:
Invoke-Command –ComputerName Production1 {Get-VM}
While this seems simple, there are a few things that you need to know about this method.
First, the Invoke-Command cmdlet does not limit you to executing a cmdlet on a single remote system. You can run a cmdlet on multiple computers. All you have to do is separate the computer names with a comma. For instance, to run this command on Production1, Production2 and Production3, the command would look like this:
Invoke-Command –ComputerName Production1, Production2, Production3 {Get-VM}
The second thing you need to know about this method is that even though it is designed to make it easy to run a single command against a remote system, you can run multiple commands. If you look at the previous line of code, you will notice that Get-VM, which is the command that is being run against the remote systems, is enclosed in braces. Anything within those braces will run on the specified remote computers. As such, you can link cmdlets together using the pipe symbol so long as all of the commands are enclosed in braces.
The third thing you need to know is that the syntax shown above only works if Kerberos authentication is being used and all of the computers, including the one on which the command is being typed, are domain-joined. Otherwise, you will have to make use of the HTTPS transport and will have to designate the remote systems as trusted hosts.
New-PSSession
The New-PSSession is commonly used to execute commands on remote systems. While Invoke-Command is designed to run a single command (or string of commands) on a remote system, New-PSSession actually redirects PowerShell to the remote server. In essence, any command that you type is automatically sent to and executed on the remote machine.
Like the Invoke-Command cmdlet, there are a number of different variations of the New-PSSession cmdlet. You can find Microsoft's documentation for this cmdlet here.
At its simplest, this cmdlet requires only that you provide the name of the remote computer. For example, if you want to establish a session with a computer named Production1, you could use this command:
New-PSSession –ComputerName Production1
This command establishes a session with the specified computer, but it doesn't automatically redirect PowerShell so any commands you type are executed on the remote system. The reason for this is that Microsoft doesn't limit you to using only one remote session. You may need to establish remote sessions with a number of different servers. As such, entering the command listed above establishes a session and PowerShell provides confirmation of the session and lists a session ID number, but that's about it.
If you want to use the remote session then you will have to make use of another PowerShell cmdlet named Enter-PSSession. Simply append the session number you want to connect to. For example, if the New-PSSession cmdlet lists 1 as the session ID for the connection to Production1, then you could enter that session by using the following command:
Enter-PSSession 1
When you use this command, you will see the PowerShell prompt change to reflect the name of the remote system. That way you can easily keep track of which system you are sending commands to.
Once again, you will need to make sure that Kerberos authentication is being used and that both systems are domain joined. Otherwise, you will have to jump through a few extra hoops in order to establish a remote session.
As you can see, PowerShell makes it easy to execute commands against remote servers. This is especially true if all of the servers and your workstation belong to a common domain.
