<p>Below is my version of azure-cli</p>

<pre><code>az --version 
</code></pre>

<blockquote>
  <p>azure-cli                         2.0.75 *  </p>
  
  <p>command-modules-nspkg              2.0.3<br>
     core                              2.0.75 *<br>
     nspkg                              3.0.4<br>
     telemetry                          1.0.4  </p>
  
  <p>Python location '/usr/local/Cellar/azure-cli/2.0.75/libexec/bin/python'<br>
     Extensions directory '/Users/alexchun/.azure/cliextensions'</p>
  
  <p>Python (Darwin) 3.7.4 (default, Oct 12 2019, 18:55:28) 
     [Clang 11.0.0 (clang-1100.0.33.8)]</p>
  
  <p>Legal docs and information: aka.ms/AzureCliLegal</p>
</blockquote>

<p>I tried to follow <a href="https://learn.microsoft.com/en-us/azure/aks/ssh" rel="nofollow noreferrer">this link</a> but there is no <em>vmss</em> found. Then I tried to run <code>az aks nodepool list --resource-group myResourceGroup --cluster-name myAKSCluster</code> to double check whether I could <a href="https://learn.microsoft.com/en-us/azure/aks/use-multiple-node-pools" rel="nofollow noreferrer">find vmss information</a> or not (as I enabled vmss when creating AKS) but with it required me to install aks-preview.</p>

<p>When I wanted to install <code>az extension add --name aks-preview</code> but with below error:</p>

<blockquote>
  <p>Unable to get extension index.<br>
  Please ensure you have network connection. Error detail: HTTPSConnectionPool(host='aka.ms',   port=443): Max retries exceeded with url: /azure-cli-extension-index-v1 (Caused by  SSLError(SSLError("bad handshake: Error([('SSL routines', 'ssl3_read_bytes', 'tlsv1 alert  internal error')])"))) </p>
</blockquote>

<p>Thus, I also tried <a href="https://learn.microsoft.com/en-us/azure/virtual-machines/extensions/vmaccess" rel="nofollow noreferrer">this method</a> to SSH Azure VM directly but failed. (I tried to SSH with manual created Ubuntu VM before successfully)</p>

<hr>

<p>Supplement:
I recreated new AKS with VMSS (enable port 22) but still could not SSH to it:
<a href="https://i.stack.imgur.com/mgzZK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mgzZK.png" alt="enter image description here"></a></p>

<p>Faced error:</p>

<blockquote>
  <p>ssh: connect to host 5x.1xx.1xx.2xx port 22: Operation timed out</p>
</blockquote>

<p>There is no External-IP and I SSH with Internal-IP but failed:
<a href="https://i.stack.imgur.com/Xp8OG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xp8OG.png" alt="enter image description here"></a></p>

<p>For your issue, the steps in the <a href="https://learn.microsoft.com/en-us/azure/aks/ssh" rel="nofollow noreferrer">link</a> is no problem. When you check the VMSS with the command here:</p>

<pre><code>CLUSTER_RESOURCE_GROUP=$(az aks show --resource-group myResourceGroup --name myAKSCluster --query nodeResourceGroup -o tsv)
SCALE_SET_NAME=$(az vmss list --resource-group $CLUSTER_RESOURCE_GROUP --query [0].name -o tsv)
</code></pre>

<p>You need to use your own resource group which the AKS cluster in. And then, if there is no information about the VMSS, it means you do not enable the VMSS when you create the AKS cluster. At this time, you just need to SSH the VMs using the means in that link.</p>

<p>Finally, maybe you can upgrade the Azure CLI to the newest version, then try to install the extension again.</p>
