Azure Policy definition structure policy rule

Article
05/24/2024

The policy rule consists of if and then blocks. In the if block, you define one or more conditions that specify when the policy is enforced. You can apply logical operators to these conditions to precisely define the scenario for a policy.

For complete details on each effect, order of evaluation, properties, and examples, see Azure Policy definitions effect basics.

In the then block, you define the effect that happens when the if conditions are fulfilled.

{
  "if": {
      <condition> | <logical operator>
  },
  "then": {
    "effect": "deny | audit | modify | denyAction | append | auditIfNotExists | deployIfNotExists | disabled"
  }
}

For more information about policyRule, go to the policy definition schema.

Logical operators

Supported logical operators are:

"not": {condition or operator}
"allOf": [{condition or operator},{condition or operator}]
"anyOf": [{condition or operator},{condition or operator}]

The not syntax inverts the result of the condition. The allOf syntax (similar to the logical and operation) requires all conditions to be true. The anyOf syntax (similar to the logical or operation) requires one or more conditions to be true.

You can nest logical operators. The following example shows a not operation that is nested within an allOf operation.

"if": {
  "allOf": [
    {
      "not": {
        "field": "tags",
        "containsKey": "application"
      }
    },
    {
      "field": "type",
      "equals": "Microsoft.Storage/storageAccounts"
    }
  ]
},

Conditions

A condition evaluates whether a value meets certain criteria. The supported conditions are:

"equals": "stringValue"
"notEquals": "stringValue"
"like": "stringValue"
"notLike": "stringValue"
"match": "stringValue"
"matchInsensitively": "stringValue"
"notMatch": "stringValue"
"notMatchInsensitively": "stringValue"
"contains": "stringValue"
"notContains": "stringValue"
"in": ["stringValue1","stringValue2"]
"notIn": ["stringValue1","stringValue2"]
"containsKey": "keyName"
"notContainsKey": "keyName"
"less": "dateValue" | "less": "stringValue" | "less": intValue
"lessOrEquals": "dateValue" | "lessOrEquals": "stringValue" | "lessOrEquals": intValue
"greater": "dateValue" | "greater": "stringValue" | "greater": intValue
"greaterOrEquals": "dateValue" | "greaterOrEquals": "stringValue" | "greaterOrEquals": intValue
"exists": "bool"

For less, lessOrEquals, greater, and greaterOrEquals, if the property type doesn't match the condition type, an error is thrown. String comparisons are made using InvariantCultureIgnoreCase.

When using the like and notLike conditions, you provide a wildcard character (*) in the value. The value shouldn't have more than one wildcard character.

When using the match and notMatch conditions, provide a hashtag (#) to match a digit, question mark (?) for a letter, and a dot (.) to match any character, and any other character to match that actual character. While match and notMatch are case-sensitive, all other conditions that evaluate a stringValue are case-insensitive. Case-insensitive alternatives are available in matchInsensitively and notMatchInsensitively.

Fields

Conditions that evaluate whether the values of properties in the resource request payload meet certain criteria can be formed using a field expression. The following fields are supported:

name
fullName
- Returns the full name of the resource. The full name of a resource is the resource name prepended by any parent resource names (for example myServer/myDatabase).
kind
type
location
- Location fields are normalized to support various formats. For example, China East 2 is considered equal to chinaeast2.
- Use global for resources that are location agnostic.
id
- Returns the resource ID of the resource that is being evaluated.
- Example: /subscriptions/11111111-1111-1111-1111-111111111111/resourceGroups/myRG/providers/Microsoft.KeyVault/vaults/myVault
identity.type
- Returns the type of managed identity enabled on the resource.
tags
tags['<tagName>']
- This bracket syntax supports tag names that have punctuation such as a hyphen, period, or space.
- Where tagName is the name of the tag to validate the condition for.
- Examples: tags['Acct.CostCenter'] where Acct.CostCenter is the name of the tag.
tags['''<tagName>''']
- This bracket syntax supports tag names that have apostrophes in it by escaping with double apostrophes.
- Where tagName is the name of the tag to validate the condition for.
- Example: tags['''My.Apostrophe.Tag'''] where 'My.Apostrophe.Tag' is the name of the tag.
Note

tags.<tagName>, tags[tagName], and tags[tag.with.dots] are still acceptable ways of declaring a tags field. However, the preferred expressions are those listed above.
property aliases - for a list, see Aliases.

Note

In field expressions referring to array alias [*] each element in the array is evaluated individually with logical and between elements. For more information, see Referencing array resource properties.

Conditions that use field expressions can replace the legacy policy definition syntax "source": "action", which used to work for write operations. For example, this is no longer supported:

{
  "source": "action",
  "like": "Microsoft.Network/publicIPAddresses/*"
}

But the desired behavior can be achieved using field logic:

{
  "field": "type",
  "equals": "Microsoft.Network/publicIPAddresses"
}

Use tags with parameters

A parameter value can be passed to a tag field. Passing a parameter to a tag field increases the flexibility of the policy definition during policy assignment.

In the following example, concat is used to create a tags field lookup for the tag named the value of the tagName parameter. If that tag doesn't exist, the modify effect is used to add the tag using the value of the same named tag set on the audited resources parent resource group by using the resourcegroup() lookup function.

{
  "if": {
    "field": "[concat('tags[', parameters('tagName'), ']')]",
    "exists": "false"
  },
  "then": {
    "effect": "modify",
    "details": {
      "operations": [
        {
          "operation": "add",
          "field": "[concat('tags[', parameters('tagName'), ']')]",
          "value": "[resourcegroup().tags[parameters('tagName')]]"
        }
      ],
      "roleDefinitionIds": [
        "/providers/microsoft.authorization/roleDefinitions/4a9ae827-6dc8-4573-8ac7-8239d42aa03f"
      ]
    }
  }
}

Value

Conditions that evaluate whether a value meets certain criteria can be formed using a value expression. Values can be literals, the values of parameters, or the returned values of any supported template functions.

Warning

If the result of a template function is an error, policy evaluation fails. A failed evaluation is an implicit deny. For more information, see avoiding template failures. Use enforcementMode of doNotEnforce to prevent impact of a failed evaluation on new or updated resources while testing and validating a new policy definition.

Value examples

This policy rule example uses value to compare the result of the resourceGroup() function and the returned name property to a like condition of *netrg. The rule denies any resource not of the Microsoft.Network/* type in any resource group whose name ends in *netrg.

{
  "if": {
    "allOf": [
      {
        "value": "[resourceGroup().name]",
        "like": "*netrg"
      },
      {
        "field": "type",
        "notLike": "Microsoft.Network/*"
      }
    ]
  },
  "then": {
    "effect": "deny"
  }
}

This policy rule example uses value to check if the result of multiple nested functions equals true. The rule denies any resource that doesn't have at least three tags.

{
  "mode": "indexed",
  "policyRule": {
    "if": {
      "value": "[less(length(field('tags')), 3)]",
      "equals": "true"
    },
    "then": {
      "effect": "deny"
    }
  }
}

Avoiding template failures

The use of template functions in value allows for many complex nested functions. If the result of a template function is an error, policy evaluation fails. A failed evaluation is an implicit deny. An example of a value that fails in certain scenarios:

{
  "policyRule": {
    "if": {
      "value": "[substring(field('name'), 0, 3)]",
      "equals": "abc"
    },
    "then": {
      "effect": "audit"
    }
  }
}

The example policy rule above uses substring() to compare the first three characters of name to abc. If name is shorter than three characters, the substring() function results in an error. This error causes the policy to become a deny effect.

Instead, use the if() function to check if the first three characters of name equal abc without allowing a name shorter than three characters to cause an error:

{
  "policyRule": {
    "if": {
      "value": "[if(greaterOrEquals(length(field('name')), 3), substring(field('name'), 0, 3), 'not starting with abc')]",
      "equals": "abc"
    },
    "then": {
      "effect": "audit"
    }
  }
}

With the revised policy rule, if() checks the length of name before trying to get a substring() on a value with fewer than three characters. If name is too short, the value "not starting with abc" is returned instead and compared to abc. A resource with a short name that doesn't begin with abc still fails the policy rule, but no longer causes an error during evaluation.

Count

Conditions that count how many members of an array meet certain criteria can be formed using a count expression. Common scenarios are checking whether 'at least one of', 'exactly one of', 'all of', or 'none of' the array members satisfy a condition. The count evaluates each array member for a condition expression and sums the true results, which is then compared to the expression operator.

Field count

Count how many members of an array in the request payload satisfy a condition expression. The structure of field count expressions is:

{
  "count": {
    "field": "<[*] alias>",
    "where": {
      /* condition expression */
    }
  },
  "<condition>": "<compare the count of true condition expression array members to this value>"
}

The following properties are used with field count:

count.field (required): Contains the path to the array and must be an array alias.
count.where (optional): The condition expression to individually evaluate for each array alias array member of count.field. If this property isn't provided, all array members with the path of 'field' are evaluated to true. Any condition can be used inside this property. Logical operators can be used inside this property to create complex evaluation requirements.
condition (required): The value is compared to the number of items that met the count.where condition expression. A numeric condition should be used.

For more details on how to work with array properties in Azure Policy, including detailed explanation on how the field count expression is evaluated, see Referencing array resource properties.

Value count

Count how many members of an array satisfy a condition. The array can be a literal array or a reference to array parameter. The structure of value count expressions is:

{
  "count": {
    "value": "<literal array | array parameter reference>",
    "name": "<index name>",
    "where": {
      /* condition expression */
    }
  },
  "<condition>": "<compare the count of true condition expression array members to this value>"
}

The following properties are used with value count:

count.value (required): The array to evaluate.
count.name (required): The index name, composed of English letters and digits. Defines a name for the value of the array member evaluated in the current iteration. The name is used for referencing the current value inside the count.where condition. Optional when the count expression isn't in a child of another count expression. When not provided, the index name is implicitly set to "default".
count.where (optional): The condition expression to individually evaluate for each array member of count.value. If this property isn't provided, all array members are evaluated to true. Any condition can be used inside this property. Logical operators can be used inside this property to create complex evaluation requirements. The value of the currently enumerated array member can be accessed by calling the current function.
condition (required): The value is compared to the number of items that met the count.where condition expression. A numeric condition should be used.

The current function

The current() function is only available inside the count.where condition. It returns the value of the array member that is currently enumerated by the count expression evaluation.

Value count usage

current(<index name defined in count.name>). For example: current('arrayMember').
current(). Allowed only when the value count expression isn't a child of another count expression. Returns the same value as above.

If the value returned by the call is an object, property accessors are supported. For example: current('objectArrayMember').property.

Field count usage

current(<the array alias defined in count.field>). For example, current('Microsoft.Test/resource/enumeratedArray[*]').
current(). Allowed only when the field count expression isn't a child of another count expression. Returns the same value as above.
current(<alias of a property of the array member>). For example, current('Microsoft.Test/resource/enumeratedArray[*].property').

Field count examples

Example 1: Check if an array is empty

{
  "count": {
    "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]"
  },
  "equals": 0
}

Example 2: Check for only one array member to meet the condition expression

{
  "count": {
    "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]",
    "where": {
      "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].description",
      "equals": "My unique description"
    }
  },
  "equals": 1
}

Example 3: Check for at least one array member to meet the condition expression

{
  "count": {
    "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]",
    "where": {
      "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].description",
      "equals": "My common description"
    }
  },
  "greaterOrEquals": 1
}

Example 4: Check that all object array members meet the condition expression

{
  "count": {
    "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]",
    "where": {
      "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].description",
      "equals": "description"
    }
  },
  "equals": "[length(field('Microsoft.Network/networkSecurityGroups/securityRules[*]'))]"
}

Example 5: Check that at least one array member matches multiple properties in the condition expression

{
  "count": {
    "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]",
    "where": {
      "allOf": [
        {
          "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].direction",
          "equals": "Inbound"
        },
        {
          "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].access",
          "equals": "Allow"
        },
        {
          "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].destinationPortRange",
          "equals": "3389"
        }
      ]
    }
  },
  "greater": 0
}

Example 6: Use current() function inside the where conditions to access the value of the currently enumerated array member in a template function. This condition checks whether a virtual network contains an address prefix that isn't under the 10.0.0.0/24 CIDR range.

{
  "count": {
    "field": "Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]",
    "where": {
      "value": "[ipRangeContains('10.0.0.0/24', current('Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]'))]",
      "equals": false
    }
  },
  "greater": 0
}

Example 7: Use field() function inside the where conditions to access the value of the currently enumerated array member. This condition checks whether a virtual network contains an address prefix that isn't under the 10.0.0.0/24 CIDR range.

{
  "count": {
    "field": "Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]",
    "where": {
      "value": "[ipRangeContains('10.0.0.0/24', first(field(('Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]')))]",
      "equals": false
    }
  },
  "greater": 0
}

Value count examples

Example 1: Check if resource name matches any of the given name patterns.

{
  "count": {
    "value": [
      "prefix1_*",
      "prefix2_*"
    ],
    "name": "pattern",
    "where": {
      "field": "name",
      "like": "[current('pattern')]"
    }
  },
  "greater": 0
}

Example 2: Check if resource name matches any of the given name patterns. The current() function doesn't specify an index name. The outcome is the same as the previous example.

{
  "count": {
    "value": [
      "prefix1_*",
      "prefix2_*"
    ],
    "where": {
      "field": "name",
      "like": "[current()]"
    }
  },
  "greater": 0
}

Example 3: Check if resource name matches any of the given name patterns provided by an array parameter.

{
  "count": {
    "value": "[parameters('namePatterns')]",
    "name": "pattern",
    "where": {
      "field": "name",
      "like": "[current('pattern')]"
    }
  },
  "greater": 0
}

Example 4: Check if any of the virtual network address prefixes isn't under the list of approved prefixes.

{
  "count": {
    "field": "Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]",
    "where": {
      "count": {
        "value": "[parameters('approvedPrefixes')]",
        "name": "approvedPrefix",
        "where": {
          "value": "[ipRangeContains(current('approvedPrefix'), current('Microsoft.Network/virtualNetworks/addressSpace.addressPrefixes[*]'))]",
          "equals": true
        },
      },
      "equals": 0
    }
  },
  "greater": 0
}

Example 5: Check that all the reserved NSG rules are defined in an NSG. The properties of the reserved NSG rules are defined in an array parameter containing objects.

Parameter value:

[
  {
    "priority": 101,
    "access": "deny",
    "direction": "inbound",
    "destinationPortRange": 22
  },
  {
    "priority": 102,
    "access": "deny",
    "direction": "inbound",
    "destinationPortRange": 3389
  }
]

Policy:

{
  "count": {
    "value": "[parameters('reservedNsgRules')]",
    "name": "reservedNsgRule",
    "where": {
      "count": {
        "field": "Microsoft.Network/networkSecurityGroups/securityRules[*]",
        "where": {
          "allOf": [
            {
              "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].priority",
              "equals": "[current('reservedNsgRule').priority]"
            },
            {
              "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].access",
              "equals": "[current('reservedNsgRule').access]"
            },
            {
              "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].direction",
              "equals": "[current('reservedNsgRule').direction]"
            },
            {
              "field": "Microsoft.Network/networkSecurityGroups/securityRules[*].destinationPortRange",
              "equals": "[current('reservedNsgRule').destinationPortRange]"
            }
          ]
        }
      },
      "equals": 1
    }
  },
  "equals": "[length(parameters('reservedNsgRules'))]"
}

Policy functions

Functions can be used to introduce additional logic into a policy rule. They are resolved within the policy rule of a policy definition and within parameter values assigned to policy definitions in an initiative.

All Resource Manager template functions are available to use within a policy rule, except the following functions and user-defined functions:

copyIndex()
dateTimeAdd()
dateTimeFromEpoch
dateTimeToEpoch
deployment()
environment()
extensionResourceId()
lambda() For more information, go to lambda
listAccountSas()
listKeys()
listSecrets()
list*
managementGroup()
newGuid()
pickZones()
providers()
reference()
resourceId()
subscriptionResourceId()
tenantResourceId()
tenant()
variables()

Note

These functions are still available within the details.deployment.properties.template portion of the template deployment in a deployIfNotExists policy definition.

The following function is available to use in a policy rule, but differs from use in an Azure Resource Manager template (ARM template):

utcNow() - Unlike an ARM template, this property can be used outside defaultValue.
- Returns a string that is set to the current date and time in Universal ISO 8601 DateTime format yyyy-MM-ddTHH:mm:ss.fffffffZ.

The following functions are only available in policy rules:

addDays(dateTime, numberOfDaysToAdd)
- dateTime: [Required] string - String in the Universal ISO 8601 DateTime format 'yyyy-MM-ddTHH:mm:ss.FFFFFFFZ'
- numberOfDaysToAdd: [Required] integer - Number of days to add
field(fieldName)
- fieldName: [Required] string - Name of the field to retrieve
- Returns the value of that field from the resource that is being evaluated by the If condition.
- field is primarily used with auditIfNotExists and deployIfNotExists to reference fields on the resource that are being evaluated. An example of this use can be seen in the DeployIfNotExists example.
requestContext().apiVersion
- Returns the API version of the request that triggered policy evaluation (example: 2021-09-01). This value is the API version that was used in the PUT/PATCH request for evaluations on resource creation/update. The latest API version is always used during compliance evaluation on existing resources.

policy()

Returns the following information about the policy that is being evaluated. Properties can be accessed from the returned object (example: [policy().assignmentId]).

{
  "assignmentId": "/subscriptions/11111111-1111-1111-1111-111111111111/providers/Microsoft.Authorization/policyAssignments/myAssignment",
  "definitionId": "/providers/Microsoft.Authorization/policyDefinitions/34c877ad-507e-4c82-993e-3452a6e0ad3c",
  "setDefinitionId": "/providers/Microsoft.Authorization/policySetDefinitions/42a694ed-f65e-42b2-aa9e-8052e9740a92",
  "definitionReferenceId": "StorageAccountNetworkACLs"
}

ipRangeContains(range, targetRange)
- range: [Required] string - String specifying a range of IP addresses to check if the targetRange is within.
- targetRange: [Required] string - String specifying a range of IP addresses to validate as included within the range.
- Returns a boolean for whether the range IP address range contains the targetRange IP address range. Empty ranges, or mixing between IP families isn't allowed and results in evaluation failure.
Supported formats:
- Single IP address (examples: 10.0.0.0, 2001:0DB8::3:FFFE)
- CIDR range (examples: 10.0.0.0/24, 2001:0DB8::/110)
- Range defined by start and end IP addresses (examples: 192.168.0.1-192.168.0.9, 2001:0DB8::-2001:0DB8::3:FFFF)
current(indexName)
- Special function that may only be used inside count expressions.

Policy function example

This policy rule example uses the resourceGroup resource function to get the name property, combined with the concat array and object function to build a like condition that enforces the resource name to start with the resource group name.

{
  "if": {
    "not": {
      "field": "name",
      "like": "[concat(resourceGroup().name,'*')]"
    }
  },
  "then": {
    "effect": "deny"
  }
}

Policy rule limits

Limits enforced during authoring

Limits to the structure of policy rules are enforced during the authoring or assignment of a policy. Attempts to create or assign policy definitions that exceed these limits will fail.

Limit	Value	Additional details
Condition expressions in the `if` condition	4096
Condition expressions in the `then` block	128	Applies to the `existenceCondition` of `auditIfNotExists` and `deployIfNotExists` policies
Policy functions per policy rule	2048
Policy function number of parameters	128	Example: `[function('parameter1', 'parameter2', ...)]`
Nested policy functions depth	64	Example: `[function(nested1(nested2(...)))]`
Policy functions expression string length	81920	Example: the length of `"[function(....)]"`
`Field count` expressions per array	5
`Value count` expressions per policy rule	10
`Value count` expression iteration count	100	For nested `Value count` expressions, this also includes the iteration count of the parent expression

Limits enforced during evaluation

Limits to the size of objects that are processed by policy functions during policy evaluation. These limits can't always be enforced during authoring since they depend on the evaluated content. For example:

{
  "field": "name",
  "equals": "[concat(field('stringPropertyA'), field('stringPropertyB'))]"
}

The length of the string created by the concat() function depends on the value of properties in the evaluated resource.

Limit	Value	Example
Length of string returned by a function	131072	`[concat(field('longString1'), field('longString2'))]`
Depth of complex objects provided as a parameter to, or returned by a function	128	`[union(field('largeObject1'), field('largeObject2'))]`
Number of nodes of complex objects provided as a parameter to, or returned by a function	32768	`[concat(field('largeArray1'), field('largeArray2'))]`