Run CLI Commands on NSX Manager Using REST API

Over the last few years I’ve had a chance to work with NSX-V REST APIs in many different shapes and forms. Directly from vRealize Orchestrator and PowerShell/PowerNSX, indirectly from vRealize Automation or simply by making calls from Postman, which is sometimes required during NSX deployment and upgrades.

To date I haven’t been able to find any gaps in the API and can say only good things about it. It is very well documented. You can find detailed descriptions of all requests in NSX API Guide PDF or interactively browse it in API explorer on https://code.vmware.com.

But at the end of the day, NSX REST API is only a subset of what you can do from CLI and there are situations where it’s not sufficient. I’ll give you an example. Let’s say you want to know how much storage is available on NSX Manager appliance log partition. There’s a REST API call, which will give you a response similar to this:

GET https://nsxm/api/1.0/appliance-management/system/storageinfo

<storageInfo>
  <totalStorage>86G</totalStorage>
  <usedStorage>22G</usedStorage>
  <freeStorage>64G</freeStorage>
  <usedPercentage>25</usedPercentage>
</storageInfo>

As you can see, it answers the question of how much total space is available on the appliance, but doesn’t provide a full per partition breakdown available from the CLI via “show filesystem”:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root       5.6G  1.2G  4.1G  23% /
tmpfs           7.9G  232K  7.9G   1% /run
devtmpfs        7.9G     0  7.9G   0% /dev
/dev/sda6        44G   19G   24G  44% /common
/dev/loop0       16G   45M   15G   1% /common/vdisk_mnt

So what are the options here? What is not widely known is that you can use NSX central command-line interface to remotely invoke appliance CLI commands using REST API.

Invoking CLI Commands

NSX REST API has a handy POST call https://nsxm/api/1.0/nsx/cli?action=execute. All you need to provide in addition to Authorization credentials using “Basic Auth” option is the following body in XML format:

<nsxcli>
  <command>show filesystem</command>
</nsxcli>

In response you will get a body in “text/plain” format, which is the only drawback of this method. You will need to parse the response in your scripting language of choice. In PowerShell, if you made the original call using Invoke-WebRequest cmdlet and saved it into the $response variable, it can look something like this:

$responseRows = $response.Content -split "`n"
foreach($row in $responseRows) {
  if($row -Like "*/dev/sda6*") {
    $pctUsed = $row.Split(" ",[StringSplitOptions]"RemoveEmptyEntries")[4]
    $pctUsedValue = $pctUsed.Substring(0, $pctUsed.Length-1)
    Write-Host "Space utilization on the log partition is $pctUsed."
    break
  }
}

Conclusion

For most use cases NSX REST API provides all the necessary information about NSX component configuration in structured JSON or XML format. This method is more of an exception rather than a rule, but it’s a nice tool to have in your tool belt, when you run out of options.

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NSX Optimistic Locking and PowerNSX

Recently, when working on some NSX-V automation, I came across an interesting issue, which I want to discuss here, since there’s almost no information on the Internet (while I’m writing this), that would help to solve it or even point you in the right direction. It has to do with PowerNSX and Optimistic Locking in NSX (which technically is not even a locking mechanism), but let’s start from the beginning.

If you ever used PowerNSX module to automate NSX via PowerShell you noticed that most of the code examples use pipelines to run PowerNSX cmdlets. So instead of using variables, like so:

$Edge = Get-NsxEdge vRA7 _ edge
$LoadBalancer = Get-NsxLoadBalancer -Edge $Edge
Set-NsxLoadBalancer -LoadBalancer $LoadBalancer -enabled
New-NsxLoadBalancerApplicationProfile -LoadBalancer $LoadBalancer -Name $WebAppProfileName -Type $VipProtocol –SslPassthrough

all commands are run this way instead:

Get-NsxEdge vRA7_edge | Get-NsxLoadBalancer | Set-NsxLoadBalancer -enabled
Get-NsxEdge vRA7_dge | Get-NsxLoadBalancer | New-NsxLoadBalancerApplicationProfile -Name $WebAppProfileName -Type $VipProtocol –SslPassthrough

What’s the difference you may ask, besides the fact the the second variant is slower, because you retrieve edge and load balancer objects multiple times, instead of once, compared to the first variant? There’s actually a strong reason for it. More specifically, it is the following error that you gonna get if you don’t use pipelines:

invoke-nsxwebrequest : Invoke-NsxWebRequest : The NSX API response received indicates a failure. 409 : Conflict : Response Body: {“errorCode”:101, “details”:”Concurrent object access error. Refresh UI or fetch the latest copy of the object and retry the operation.”, “rootCauseString”:null, “moduleName”:null, “errorData”:null}

See, NSX uses Optimistic Locking (yes, there’s Pessimistic Locking as well) to handle concurrency. Its purpose is to make sure that if you’re making a change to an object in NSX you are aware of its current state. In the above example, you saved load balancer into a variable, changed the load balancer state to enabled and then tried to create an application profile, supplying load balancer saved in a variable as a parameter to the cmdlet. But the load balancer (and edge) state has changed and you’re basically using an old (stale) version of the object. You either have to retrieve the current state of the object again or avoid this issue all together by simply using pipelines and retrieve the up-to-date version of the object with every call.

Read this article if you want to know more about Optimistic Locking:

• https://enterprisecraftsmanship.com/2017/09/18/optimistic-locking-automatic-retry/

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