Scale up Kubernetes cluster in Azure

Problem

Unexpectedly your Web Applications became a hit and you need to scale up your application. Your application is being hosted on a Kubernetes cluster. The cluster was created using `acs-engine` with X nodes but now it has to be scaled up to Y nodes.

Conditions that need to be met:

• Zero Downtime.
• Current nodes (VMs) need to go unchanged.

Solution

In case that the cluster was created using AKS (Azure Container Services) the solution is simple and doesn’t warrant another article. Just execute the command:

az acs scale -g myResourceGroup -n containerservice-myACSName --new-agent-count 10

The solution described is for clusters created using the acs-engine. This requires manual intervention in the generated ARM templates.

Let’s get started.

• Open your `azuredeploy.json` and delete the resource Microsoft.Network/networkSecurityGroups. This includes the entire section below:

{
  "apiVersion": "[variables('apiVersionDefault')]",
  "location": "[variables('location')]",
  "name": "[variables('nsgName')]",
  "properties": {
    "securityRules": [
      {
        "name": "allow_ssh",
        "properties": {
            # SHORTENED FOR BREVITY
        }
      },
      {
        "name": "allow_kube_tls",
        "properties": {
            # SHORTENED FOR BREVITY
        }
      }
    ]
  },
  "type": "Microsoft.Network/networkSecurityGroups"
},

• Delete dependency of the VNet resource o the networkSecurityGroup, by deleting the following line:

"dependsOn": [
    "[concat('Microsoft.Network/networkSecurityGroups/', variables('nsgName'))]" ## DELETE THIS LINE <<<<<<<
],

"agentpool1Count": {
  "value": X          
},

"agentpool1Count": {
  "value": Y          
},
"agentpool1Offset": { 
  "value": X          
},

az group deployment create --name [DEPLOYMENT_NAME] --resource-group [K8S_CLUSTER_RG] --template-file "[path to updated ./azuredeploy.json]" --parameters "[path to updated azuredeploy.parameters.json]"