Azure / , Automation / Dec. 14, 2018 / Matt Davies | Partner

Lazy Afternoons with Azure ARM Conditionals

Like many IT professionals I spent my early years in the industry working in customer oriented support roles. Working in a support role can be challenging. You are the interface between the people who consume IT services and the complexity of the IT department. You interact with a broad range of people who use the IT services you are responsible for to do the real work of the business. Positives include broad exposure to a wide range of issues and personality types. Some of the roles I worked in had the downside of repetitive reactive work, however, the flip side to this is, that this is where I really started to understand the value proposition of automation

Like many IT professionals I spent my early years in the industry working in customer oriented support roles. Working in a support role can be challenging. You are the interface between the people who consume IT services and the complexity of the IT department. You interact with a broad range of people who use the IT services you are responsible for to do the real work of the business. Positives include broad exposure to a wide range of issues and personality types. Some of the roles I worked in had the downside of repetitive reactive work, however, the flip side to this is, that this is where I really started to understand the value proposition of automation.

Unfortunately the nature of being subjected to reactive support work and grumpy frustrated consumers is you can fall into the trap of just going through the motions and become caught in a cycle of just doing a good job and not striving to make a real difference. Not this late in the day. . . This phrase was used by a co-worker who for anonymity purposes we will call “Barry”. Barry had grown tired of changes to the cyclical rhythm of his daily support routine and at the slightest suggestion of any activity or initiative that came remotely close to threatening a lazy afternoon would be rebutted with “Not this late in the day. . .” Sometimes not this late in the day could have been interchanged with not this late in the year. . .sigh.

What I learnt from Barry, is there is no need to do repetitive tasks. Humans are terrible at this, despite best intentions we make mistakes which introduce subtle differences into environments, this almost always causes stability and reliability issues and no one wants that. We all like lazy afternoons, so in the spirit of doing more with less I’d like to share some examples of how the use of conditionals within ARM templates will change your life. . .well maybe just make your afternoon a little easier and the consumers of your services happier. . . Win!

Conditionals support in ARM has been around for a little while now, but are not as widely used as I believe they should be. Conditionals are useful in scenarios where you may want to optionally include a resource that would have previously required the use of separate templates or complex nesting scenarios.

In the following example I am provisioning a virtual machine and I want to optionally include a data disk and/or a public IP.

In the parameters section of the ARM template I’ve included a couple of parameters to determine if we want to create a public IP (pip) and a Data Disk (dataDisk) as follows:


"pip": {
"type": "string",
"allowedValues": [
"Yes",
"No"
],
"metadata": {
"description": "Select whether the VM should have a public ip."
}
},
"dataDisk": {
"type": "string",
"allowedValues": [
"Yes",
"No"
],
"metadata": {
"description": "Select whether the VM should have an additional data disk."
}
},

In the variables section I’ve defined a public IP object and a dataDisk array. I’ll use these values later if “Yes” is chosen for either my pip or dataDisk.


"pipObject": {
"id": "[resourceId('Microsoft.Network/publicIPAddresses',variables('publicIPAddressName'))]"
},
"dataDisks": [
{
"name": "[concat(parameters('virtualMachineName'),'_Data1')]",
"caching": "None",
"diskSizeGB": "[parameters('vmDataDisk1Size')]",
"lun": 0,
"createOption": "Empty",
"managedDisk": {
"storageAccountType": "[parameters('vmDataDisk1Sku')]"
}
}
]

Condition is an optional keyword that you can use with any of the resource objects within your ARM templates. To make it easily identifiable as a conditionally deployed resource, I’d suggest placing above the other required keywords of the resource.
Conditionally create a public IP resource by adding a “condition”: keyword. I’m using an equals comparison function to determine if the pip parameter is set to “Yes” or “No”. In this case, if its set to “Yes”, then the resource is created.


{
"condition": "[equals(parameters('pip'), 'Yes')]",
"apiVersion": "2015-06-15",
"type": "Microsoft.Network/publicIPAddresses",
"name": "[variables('publicIPAddressName')]",
"location": "[parameters('location')]",
"properties": {
"publicIPAllocationMethod": "[variables('publicIPAddressType')]",
"dnsSettings": {
"domainNameLabel": "[variables('dnsNameForPublicIP')]"
}
}
},

Ok so far that’s pretty straight forward, the tricky part is how we tell other resources that consume our public IP about it (like the network interface) in the condition where we have created a public IP we need to provide a pipObject containing a resourceId for the “id”: keyword. Or in the case of not creating a public IP we need to provide a null value. For this I’ve chosen to use a “if” logical function in conjunction with the “equals” comparison function to either provide the aforementioned resourceId or a json null value.


{
"name": "[toLower(concat('nic',parameters('virtualMachineName')))]",
"type": "Microsoft.Network/networkInterfaces",
"apiVersion": "2018-04-01",
"location": "[parameters('location')]",
"properties": {
"ipConfigurations": [
{
"name": "ipconfig1",
"properties": {
"subnet": {
"id": "[variables('subnetRef')]"
},
"privateIPAllocationMethod": "Dynamic",
"publicIPAddress": "[if(equals(parameters('pip'), 'Yes'), variables('pipObject'), json('null'))]"
}
}
]
},

Similarly I am doing much the same thing with the dataDisk


{
"name": "[parameters('virtualMachineName')]",
"type": "Microsoft.Compute/virtualMachines",
"apiVersion": "2018-06-01",
"location": "[parameters('location')]",
"dependsOn": [
"[resourceid('Microsoft.Network/networkInterfaces/', toLower(concat('nic',parameters('virtualMachineName'))))]"
],
"properties": {
"hardwareProfile": {
"vmSize": "[parameters('virtualMachineSize')]"
},
"storageProfile": {
"imageReference": {
"publisher": "SUSE",
"offer": "SLES-Standard",
"sku": "12-SP3",
"version": "latest"
},
"osDisk": {
"name": "[concat(parameters('virtualMachineName'),copyIndex(1))]",
"createOption": "fromImage"
},
"dataDisks": "[if(equals(parameters('dataDisk'), 'Yes'), variables('dataDisks'), json('null'))]"
},
"networkProfile": {
"networkInterfaces": [
{
"id": "[resourceid('Microsoft.Network/networkInterfaces/', toLower(concat('nic',parameters('virtualMachineName'))))]"
}
]
},
"osProfile": {
"computerName": "[parameters('virtualMachineName')]",
"adminUsername": "[parameters('adminUsername')]",
"adminPassword": "[parameters('adminPassword')]"
}
}
}

So there we have it, the use of conditionals has reduced the need for more complex scenarios like nested templates or multiple templates for different scenarios. Next time you get a request that’s not the status quo perhaps you can accommodate it with a few conditionals. . . Now back to my lazy afternoon.

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