Tag Archives: EVC using pyVmomi

Simple workaround: Adding a host to an empty EVC cluster fails on latest vCenter patch

This article is motivated by this VMTN thread posted by one of VMware users. I see that several users have reported this usability issue. Issue reported was: Users are NOT able to add a host into an empty EVC cluster after applying latest vCenter patch, which was released as part of Hypervisor-Assisted Guest Mitigation. In this post, I thought to share my understanding about this “empty EVC cluster” behavior along with simple workaround to fix this usability issue. In order to explore this further, I created a empty EVC cluster on vCenter 6.5 U1e as shown below.

You can see, I have created empty EVC cluster, where EVC mode configured is “Intel-IvyBridge”. Now I tried adding a host, where corresponding ESXi patch is NOT applied and as posted on VMTN thread, I see below error on web client.

Now question is why does it fail with this latest patch? You might know that as part of VMware patches released for Hypervisor-Assisted Guest Mitigation, there are three new cpuids got exposed i.e. cpuid.IBRS , cpuid.IBPB & cpuid.STIBP. Now we need to know whether these new cpuids are exposed by the “empty EVC cluster” that we just created but you might be wondering how to go about it? It is fairly simple to know it by using one of EVC API properties as posted in my tutorial post on EVC vSphere APIs. As part of section #4 of that tutorial i.e. “Exploring EVC Cluster state”, I had written a pyVmomi script to get the EVC cluster state i.e. getEVCClusterState.py. I little modified this script to know whether new cpuids are exposed by cluster or not. Below is the code snippet.

#Cluster object for empty EVC cluster
cluster = get_obj(content,[vim.ClusterComputeResource],cluster_name)
#EVCManager which exposes EVC APIs

current_evcmode_key= evc_state.currentEVCModeKey

        print "Current EVC Mode::"+current_evcmode_key
        print "EVC is NOT enabled on the cluster"

#getting feature capabilities available on cluster
feature_capabilities = evc_state.featureCapability

for capability in feature_capabilities:

        if(capability.key=="cpuid.STIBP" and capability.value=="1"):
                print "Found new cpuid::"+ capability.key

        if(capability.key=="cpuid.IBPB" and capability.value=="1"):
                print "Found new cpuid::"+ capability.key

        if(capability.key=="cpuid.IBRS" and capability.value=="1"):
                print "Found new cpuid::"+ capability.key
if(not flag):
        print "No new cpubit found"

Once I executed above script on “empty EVC cluster” and I see output as follows

vmware@localhost:~$ python emptyEVCCluster.py
Current EVC Mode::intel-ivybridge
Found new cpuid::cpuid.IBPB
Found new cpuid::cpuid.IBRS
Found new cpuid::cpuid.STIBP

Output clearly shows that new cpuids are exposed on the “empty EVC cluster” that we created on latest vCenter patch. This concludes that when you try to add a non-patched host into this cluster, it will fail since that host does NOT support these new cpuids. On the other hand, if you have applied corresponding ESXi patch (which is pulled back at the moment), then you will not face this issue as new cpuids are available on that patched host. Now that you understood this behavior, let us take a look at the simple workaround to fix this issue.

What is the workaround?
I understand, this is a problem from usability perspective but good news is that we have very simple workaround available i.e. Instead of upfront enabling EVC on the empty cluster, you can create non-EVC cluster first , add all possible hosts into it and finally enable EVC as per available EVC mode. If you ask me, it is always good idea to create non-EVC cluster and only after adding all possible hosts, we should finally enable EVC on cluster.

I would also recommend you to read “vMotion and EVC Information” section from VMware KB to understand EVC and vMotion behavior post applying these patches.

Some useful resources on EVC
1. Part-1: Managing EVC using pyVmomi
2. Part 2: Managing EVC using pyVmomi
3. Tutorial on getting started pyVmomi

I hope you enjoyed this post, let me know if you have any questions/doubts.

Tutorial: Part-2 : How to Manage EVC using vSphere Python SDK pyVmomi?

In part-1, we explored EVC enable, disable APIs & some important EVC properties using pyVmomi. In part-2, we would explore left out EVC APIs from part-1 i.e.CheckConfigureEvcMode_Task() & CheckAddHostEvc_Task(). In addition, we will also take a look at some more important EVC properties required to manage EVC end to end.

1. Checking whether EVC can be configured on existing cluster or not?
CheckConfigureEvcMode_Task() is responsible for checking exactly the same. If you have existing cluster with several hosts and if you would like to evaluate whether EVC can be enabled on cluster or not on particular EVCMode key, this API is really handy. If it is not possible to enable EVC on particular cluster, this API will return not only the set of reasons why it can fail to configure EVC but also the set of hosts those are causing it to fail. Before we start, below are the set of hosts present in cluster already.

vmware@localhost:~$ python getMaxEVCModeonHost.py

To start with, the way we did in part-1, we will check whether EVC can be enabled on “intel-broadwell” EVCMode key. As we learned in last post, EVC should not be able to configure on this cluster with EVCMode “intel-broadwell”. Let us see whether API properly returns right reason and host that is causing it.

Below script is available on my git-hub repo as well

from pyVim.connect import SmartConnect, Disconnect
from pyVmomi import vim
import atexit
import ssl
import sys
import time

#Script to check whether EVC can be enabled on cluster with given EVCMode

si= SmartConnect(host="", user="Administrator@vsphere.local", pwd="VMware#12",sslContext=s)

# Below method helps us to get MOR of the object (vim type) that we passed.
def get_obj(content, vimtype, name):
        obj = None
        container = content.viewManager.CreateContainerView(content.rootFolder, vimtype, True)
        for c in container.view:
                if name:
                        if c.name == name:
                                obj = c
                                obj = None                          
        return obj

#Cluster object
cluster = get_obj(content,[vim.ClusterComputeResource],cluster_name)

print "ClusterName::"+cluster.name

checkResult= task.info.result

         print "EVC can not be enabled on this cluster, please take look at below reasons and hosts causing this issue"
        for result in checkResult:
                print result.error.msg
                for h in result.host:
                        print h.name
                print "---------------------"
        print "EVC can be successfully enabled on the cluster with no issues"

atexit.register(Disconnect, si)

vmware@localhost:~$ python checkEVC.py
EVC can not be enabled on this cluster, please take look at below reasons and hosts causing this issue
The host’s CPU hardware does not support the cluster’s current Enhanced vMotion Compatibility mode. The host CPU lacks features required by that mode.

isn’t this error matching with this screenshot from Part-1?

Note: If you notice on line #38, CheckConfigureEvcMode_Task() API returns ClusterEVCManagerCheckResult only when EVC can NOT be configured on the cluster.

Now I did powerON one of the VMs on host, which has max EVCMode as “intel-broadwell” and executed above script but this time passed EVCMode key as “intel-sandybridge”. Let us take a look at output.

vmware@localhost:~$ python checkEVC.py
EVC can not be enabled on this cluster, please take look at below reasons and hosts causing this issue
The host cannot be admitted to the cluster’s current Enhanced vMotion Compatibility mode. Powered-on or suspended virtual machines on the host may be using CPU features hidden by that mode.

You can see, EVC configuration failed since one of VM was powered ON, which is using some cpu features those are NOT available on “intel-sandybridge” EVC mode. This is expected and error is exactly matching with web client screenshot from Part-1.

Now I powered-off the VM residing on “intel-broadwell” based host & Powered-ON VM on host, which support max EVCMOde as “intel-sandybridge”. Finally executed same checkEVC.py script and below is the output.

vmware@localhost:~$ python checkEVC.py
EVC can be succesfully enabled on the cluster with no issues

wasn’t output cool? Note that VM was up on host with “intel-sandybridge” host and EVCMode used was also “intel-sandybridge”, hence EVC will be configured successfully. Now let us move on to next EVC API.

2. Checking whether host can be added into existing EVC enabled cluster or not?
CheckAddHostEvc_Task() API allows user to check exactly the same. This API accepts HostSpec as paramter for the host to be checked and below is the code snippet. I will leave it to you in order to try this API in your environment.

print host_conn_spec

That is all about EVC APIs. I hope Part-1 & Part-2 have given you good insight into how to play around EVC APIs. Stay tuned for my next post. Please comment if you have any query.