High-level notes on Azure ARM Templates

Expressions

• enclose expressions in []
• expressions can appear anywhere in a JSON string value
• expressions return another JSON value
• use [[ to escape
• expression evaluation happens on template deployment
• question : can a parameters.json file contain an expression? My experience says no.

Parameters

• to specify an optional parameter, provide a defaultValue
• secureString and secureObject parameter types are opaque after deployment

Variables

We can creatively use variables to create conditional logic.

Output

Output is useful for inspecting parameters during tests of the deployment.

Functions

• Some functions are not supported in variables . E.g. listKeys is not.

Examples

Example: conditional logic with variables.

"parameters": {
   "envName": {
     "type": "string",
     "allowedValues": [
       "test",
       "prod"
     ]
   }
},
"variables": {
   "envSettings": {
     "test": {
       "instancesSize": "Small",
       "instancesCount": 1
     },
     "prod": {
       "instancesSize": "Large",
       "instancesCount": 4
     }
   },
   "currentEnvSettings": "[variables('envSettings')[parameters('envName')]]",
   "instancesSize": "[variables('currentEnvSettings').instancesSize]",
   "instancesCount": "[variables('currentEnvSettings').instancesCount]"
}

Example: output the instance size.

"outputs": {
   "actualInstanceSize" : {
     "type" : "string",
     "value": "[variables('instanceSize')]"
   }
}

See

https://docs.microsoft.com/en-us/azure/azure-resource-manager/resource-group-authoring-templates