Resource Orchestration Service (ROS) provides several built-in functions to help you manage stacks. You can use built-in functions to define Resources and Outputs.

You can use the following built-in functions in templates: Fn::Str, Fn::Base64Encode, Fn::Base64Decode, Fn::FindInMap, Fn::GetAtt, Fn::Join, Fn::Select, Ref, Fn::GetAZs, Fn::Replace, Fn::Split, Fn::Equals, Fn::And, Fn::Or, Fn::Not, Fn::If, Fn::ListMerge, Fn::GetJsonValue, Fn::MergeMapToList, Fn::Avg, Fn::SelectMapList, Fn::Add, Fn::Calculate, Fn::GetAtt, and Fn::Sub.

Fn::Str

The Fn::Str function is used to return the string representation of a value.

Declaration 
"Fn::Str" : toString

Parameters

toString: the value of the number or integer type to be converted to a string.

Return value

The string representation of the value.

Examples 
{"Fn::Str": 123456}

"123456" is returned in this example.

Fn::Base64Encode

The Fn::Base64Encode function is used to return the Base64 representation of the input string.

Declaration 
"Fn::Base64Encode": "stringToEncode"

Parameters

stringToEncode: the string to be encoded in Base64.

Return value

The Base64 representation of the input string.

Examples 
{"Fn::Base64Encode": "string to encode"}

c3RyaW5nIHRvIGVuY29kZQ== is returned in this example.

Fn::Base64Decode

The Fn::Base64Decode function is used to return a string decoded from a Base64-encoded string.

Declaration 
{"Fn::Base64Decode": "stringToEncode"}

Parameters

stringToDecode: the string decoded from the Base64-encoded string.

Return value

The string decoded from the Base64-encoded string.

Examples

{"Fn::Base64Decode": "c3RyaW5nIHRvIGVuY29kZQ=="}

string to encode is returned in this example.

Fn::FindInMap

The Fn::FindInMap function is used to return the values based on keys in a two-level mapping that is declared in the Mappings section.

Declaration

"Fn::FindInMap": ["MapName", "TopLevelKey", "SecondLevelKey"]
Parameters
  • MapName: the ID of a mapping declared in the Mappings section that contains keys and values.
  • TopLevelKey: the top-level key name. The value is a list of key-value pairs.
  • SecondLevelKey: the second-level key name. The value is a string or a number.

Return value

The value that is assigned to the SecondLevelKey parameter.

Examples

The ImageId property must be specified when you create a WebServer instance. The Mappings section describes the ImageId mappings by region. The Parameters section describes the regions that must be specified by template users. Fn::FindInMap finds the corresponding ImageId mapping in RegionMap based on the region specified by a user, and then finds the corresponding ImageId in the mapping.
  • MapName is set to the map of interest, which is "RegionMap" in this example.
  • TopLevelKey is set to the region where the stack is created, which is { "Ref" : "regionParam" } in this example.
  • SecondLevelKey is set to the required architecture, which is "32" in this example. 
{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "regionParam": {
      "Description": "The region where the ECS instance is created",
      "Type": "String",
      "AllowedValues": [
        "hangzhou",
        "beijing"
      ]
    }
  },
  "Mappings": {
    "RegionMap": {
      "hangzhou": {
        "32": "m-25l0rcfjo",
        "64": "m-25l0rcfj1"
      },
      "beijing": {
        "32": "m-25l0rcfj2",
        "64": "m-25l0rcfj3"
      }
    }
  },
  "Resources": {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId": {
          "Fn::FindInMap": [
            "RegionMap",
            {"Ref": "regionParam"},
            "32"
          ]
        },
        "InstanceType": "ecs.t1.small",
        "SecurityGroupId": "sg-25zwc****",
        "ZoneId": "cn-beijing-b",
        "Tags": [
          {
            "Key": "key1",
            "Value": "value1"
          },
          {
            "Key": "key2",
            "Value": "value2"
          }
        ]
      }
    }
  }
}
Supported functions
  • Fn::FindInMap
  • Ref

Fn::GetAtt

The Fn::GetAtt function is used to return the value of a property from a resource in a template.

Declaration

"Fn::GetAtt": ["resourceID", "attributeName"]
Parameters
  • resourceID: the ID of the resource.
  • attributeName: the name of the resource property.

Return value

The value of the resource property.

Examples

The ImageId property of MyEcsInstance is returned in this example. 
{"Fn::GetAtt" : ["MyEcsInstance" , "ImageID"]}

Fn::Join

The Fn::Join function is used to append a set of values into a single value that is separated by a specified delimiter.

Declaration 
{"Fn::Join": ["delimiter", ["string1", "string2", ... ]]}
Parameters
  • delimiter: the value used to divide the string. The delimiter value can be left blank so that all the values are directly combined.
  • [ "string1", "string2", ... ]: the list of values that are combined into a string.

Return value

The combined string.

Examples 
{"Fn::Join": [ ",", ["a", "b", "c"]]}

"a,b,c" is returned in this example.

Supported functions

  • Fn::Base64Encode
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref

Fn::Select

The Fn::Select function is used to return a single data element from a list of data elements by an index.

Declaration
  • The following example assumes that the list of data elements is an array: 
    "Fn::Select": ["index", ["value1", "value2", ... ]]
  • The following example assumes that the list of data elements is a mapping table: 
    "Fn::Select": ["index", {"key1": "value1", ... }]

Parameters

index: the index of the object data element. If the list of data elements is an array, the index must be an integer ranging from 0 to N-1, where N indicates the number of elements in the array. If the list of data elements is a mapping table, the index must be a key in the mapping table.

If the corresponding value of the index cannot be found, the system returns an empty string.

Return value

The object data element

Examples
  • The following example assumes that the list of data elements is an array: 
    {"Fn::Select": ["1", ["apples", "grapes", "oranges", "mangoes"]]}

    "grapes" is returned in this example.

  • The following example assumes that the list of data elements is a mapping table: 
    {"Fn::Select": ["key1", {"key1": "grapes", "key2": "mangoes"}]}

    "grapes" is returned in this example.

  • The following example assumes that the list of data elements is a comma-delimited list: 
    "Parameters": {
  "userParam": {
    "Type": "CommaDelimitedList",
      "Default": "10.0.XX.XX, 10.0.XX.XX, 10.0.XX.XX"
  }
}

"Resources": {
  "resourceID": {
      "Properties": {
          "CidrBlock": {"Fn::Select": ["0", {"Ref": "userParam"}]}
    }
  }
}

Supported functions

For the Fn::Select index value, you can use the Ref function.

For the Fn::Select list of data elements, you can use the following functions:

  • Fn::Base64Encode
  • Fn::FindInMap
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref

Ref

The Ref function is used to return the value of a specified parameter or resource.

If the specified parameter is a resource ID, the value of the resource is returned. Otherwise, the system will return the value of the specified parameter.

Declaration

"Ref": "logicalName"

Parameters

logicalName: the logical name of the resource or parameter that you want to reference.

Return value

The value of the resource or parameter.

Examples

The following example uses the Ref function to specify regionParam as the region parameter for RegionMap of WebServer: 

{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "regionParam": {
      "Description": "The region where the ECS instance is created",
      "Type": "String",
      "AllowedValues": [
        "hangzhou",
        "beijing"
      ]
    }
  },
  "Mappings": {
    "RegionMap": {
      "hangzhou": {
        "32": "m-25l0rcfjo",
        "64": "m-25l0rcfj1"
      },
      "beijing": {
        "32": "m-25l0rcfj2",
        "64": "m-25l0rcfj3"
      }
    }
  },
  "Resources": {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId": {
          "Fn::FindInMap": [
            "RegionMap",
            {"Ref": "regionParam"},
            "32"
          ]
        },
        "InstanceType": "ecs.t1.small",
        "SecurityGroupId": "sg-25zwc****",
        "ZoneId": "cn-beijing-b",
        "Tags": [
          {
            "Key": "tiantt",
            "Value": "ros"
          },
          {
            "Key": "tiantt1",
            "Value": "ros1"
          }
        ]
      }
    }
  }
}

Supported functions

When you use Ref function you cannot use other functions in it at the same time. You must specify a string value for the resource logical ID.

Fn::GetAZs

The Fn::GetAZs function is used to return a list of zones for a specified region.

Note Use the function only for ECS and VPC resources.
Declaration 
"Fn::GetAZs": "region"

Parameters

region: the ID of the region.

Return value

The list of zones for the specified region.

Examples

The following example demonstrates how to create an ECS instance in the first zone of a specified region: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Resources" : {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId": "centos7u2_64_40G_cloudinit_2016072****",
        "InstanceType": "ecs.n1.tiny",
        "SecurityGroupId": "sg-2zedcm7ep5quses0****",
        "Password": "Ros1****",
        "AllocatePublicIP": true,
        "InternetChargeType": "PayByTraffic",
        "InternetMaxBandwidthIn": 100,
        "InternetMaxBandwidthOut": 100,
        "SystemDiskCategory": "cloud_efficiency",
        "IoOptimized": "optimized",
        "ZoneId": {"Fn::Select": ["0", {"Fn::GetAZs": {"Ref": "ALIYUN::Region"}}]}
      }
    }
  },
  "Outputs": {
    "InstanceId": {
         "Value": {"Fn::GetAtt": ["WebServer","InstanceId"]}
    },
    "PublicIp": {
         "Value": {"Fn::GetAtt": ["WebServer","PublicIp"]}
    }
  }
}

Supported functions

  • Fn::Base64Encode
  • Fn::FindInMap
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref

Fn::Replace

The Fn::Replace function is used to replace a specified substring contained in a string with a new substring.

Declaration 
{"Fn::Replace": [{"object_key": "object_value"}, "object_string"]}
Parameters
  • object_key: the substring to be replaced.
  • object_value: the new substring to replace the previous substring.
  • object_string: the string whose object_key is replaced.

Return value

The string after replacement.

Examples

The following example demonstrates how to replace "print" with "echo" in the specified script: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Resources" : {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId" : "centos_7_2_64_40G_base_20170222****",
        "InstanceType": "ecs.n1.medium",
        "SecurityGroupId": "sg-94q49****",
        "Password": "MytestPassword****",
        "IoOptimized": "optimized",
        "VSwitchId": "vsw-94vdv****",
        "VpcId": "vpc-949uz****",
        "SystemDiskCategory": "cloud_ssd",
        "UserData": {"Fn::Replace": [{"print": "echo"},
         {"Fn::Join": ["", [
             "#! /bin/sh\n",
             "mkdir ~/test_ros\n",
             "print hello > ~/1.txt\n"
         ]]}]}
      }
    }
  },
  "Outputs": {
    "InstanceId": {
         "Value" : {"Fn::GetAtt": ["WebServer","InstanceId"]}
    },
    "PublicIp": {
         "Value" : {"Fn::GetAtt": ["WebServer","PublicIp"]}
    }
  }
}

Supported functions

  • Fn::Base64Encode
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref

Fn::Split

The Fn::Split function is used to split a string into a list of values separated by a specified delimiter and return the list.

Declaration 
"Fn::Split": ["delim",  "original_string"]
Parameters
  • delim: the specified delimiter, which can be ,, ;, \n, \t.
  • original_string: the string to be split.

Return value

A list of string values.

Examples
  • The following example assumes that the list of data elements is an array: 
    {"Fn::Split": [";", "foo; bar; achoo"]}

    ["foo", " bar", "achoo "] is returned in this example.

  • The following example uses Fn::Split to split InstanceIds: 
    {
  "Parameters": {
    "InstanceIds": {
      "Type": "String",
      "Default": "instane1_id,instance2_id,instance2_id"
    }
  },
  "Resources": {
    "resourceID": {
      "Type": "ALIYUN::SLB::BackendServerAttachment",
      "Properties": {
        "BackendServerList": {
          "Fn::Split": [
            ",",
            {
              "Ref": "InstanceIds"
            }
          ]
        }
      }
    }
  }
}

Supported functions

  • Fn::Base64Encode
  • Fn::FindInMap
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Fn::Replace
  • Fn::GetAZs
  • Fn::If
  • Ref

Fn::Equals

The Fn::Equals function is used to compare whether two values are equal. If the two values are equal, true is returned. If the two values are not equal, false is returned.

Declaration

{"Fn::Equals": ["value_1", "value_2"]}

Parameters

value: the values to be compared.

Return value

true or false.

Examples

The following example uses Fn::Equals to define a condition in the Conditions section: 
{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "EnvType": {
      "Default": "pre",
      "Type": "String"
    }
  },
  "Conditions": {
    "TestEqualsCond": {
      "Fn::Equals": [
        "prod",
        {"Ref": "EnvType"}
      ]
    }
  }
}

Supported functions

  • Fn::Or
  • Fn::Not
  • Fn::Equals
  • Fn::FindInMap
  • Fn::And
  • Ref

Fn::And

The Fn::And function is used to represent the AND operator, and must contain at least two conditions. If all the specified conditions are evaluated as true, true is returned. If any condition is evaluated as false, false is returned.

Declaration 
{"Fn::And": ["condition", {...}]}

Parameters

condition: the condition to be evaluated.

Return value

true or false.

Examples

The following example uses Fn::And to define a condition in the Conditions section: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Parameters":{
    "EnvType":{
      "Default":"pre",
      "Type":"String"
    }
  },
  "Conditions": {
    "TestEqualsCond": {"Fn::Equals": ["prod", {"Ref": "EnvType"}]},
    "TestAndCond": {"Fn::And": ["TestEqualsCond", {"Fn::Equals": ["pre", {"Ref": "EnvType"}]}]}
  }
}

Supported functions

  • Fn::Or
  • Fn::Not
  • Fn::Equals
  • Fn::FindInMap
  • Fn::And
  • Ref

Fn::Or

The Fn::Or function is used to represent the OR operator, and must contain at least two conditions. If any specified condition is evaluated as true, true is returned. If all the conditions are evaluated as false, false is returned.

Declaration

{"Fn::Or": ["condition", {...}]}

Parameters

condition: the condition to be evaluated.

Return value

true or false.

Examples

The following example uses Fn::Or to define a condition in the Conditions section: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Parameters":{
    "EnvType":{
      "Default":"pre",
      "Type":"String"
    }
  },
  "Conditions": {
    "TestEqualsCond": {"Fn::Equals": ["prod", {"Ref": "EnvType"}]},
    "TestOrCond": {"Fn::And": ["TestEqualsCond", {"Fn::Equals": ["pre", {"Ref": "EnvType"}]}]}
  }
}

Supported functions

  • Fn::Or
  • Fn::Not
  • Fn::Equals
  • Fn::FindInMap
  • Fn::And
  • Ref

Fn::Not

The Fn::Not function is used to represent the NOT operator. If a condition is evaluated as false, true is returned. If a condition is evaluated as true, false is returned.

Declaration

{"Fn::Not": "condition"}

Parameters

condition: the condition to be evaluated.

Return value

true or false.

Examples

The following example uses Fn::Not to define a condition in the Conditions section: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Parameters":{
    "EnvType":{
      "Default":"pre",
      "Type":"String"
    }
  },
  "Conditions": {
    "TestNotCond": {"Fn::Not": {"Fn::Equals": ["pre", {"Ref": "EnvType"}]}}
  }
}

Supported functions

  • Fn::Or
  • Fn::Not
  • Fn::Equals
  • Fn::FindInMap
  • Fn::And
  • Ref

Fn::If

This function returns one of two possible values. If a specified condition is evaluated as true, one value is returned. If the specified condition is evaluated as false, the other value is returned. The property values of Resources and Outputs in templates support the Fn::If function. You can use the ALIYUN::NoValue pseudo parameter as the return value to delete the corresponding property.

Declaration 
{"Fn::If": ["condition_name", "value_if_true", "value_if_false"]}
Parameters
  • condition_name: the name of the condition in the Conditions section. A condition is referenced by using the condition name.
  • value_if_true: If the specified condition is evaluated as true, this value is returned.
  • value_if_false: If the specified condition is evaluated as false, this value is returned.

Examples

The following example demonstrates how to determine whether to create a data disk based on input parameters: 
{
    "ROSTemplateFormatVersion":"2015-09-01",
    "Parameters":{
        "EnvType":{
            "Default":"pre",
            "Type":"String"
        }
    },
    "Conditions":{
        "CreateDisk":{
            "Fn::Equals":[
                "prod",
                {
                    "Ref":"EnvType"
                }
            ]
        }
    },
    "Resources":{
        "WebServer":{
            "Type":"ALIYUN::ECS::Instance",
            "Properties":{
                "DiskMappings":{
                    "Fn::If":[
                        "CreateDisk",
                        [
                            {
                                "Category":"cloud_efficiency",
                                "DiskName":"FirstDataDiskName",
                                "Size":40
                            },
                            {
                                "Category":"cloud_ssd",
                                "DiskName":"SecondDataDiskName",
                                "Size":40
                            }
                        ],
                        {
                            "Ref":"ALIYUN::NoValue"
                        }
                    ]
                },
                "VpcId":"vpc-2zew9pxh2yirtzqxd****",
                "SystemDiskCategory":"cloud_efficiency",
                "SecurityGroupId":"sg-2zece6wcqriejf1v****",
                "SystemDiskSize":40,
                "ImageId":"centos_6_8_64_40G_base_20170222****",
                "IoOptimized":"optimized",
                "VSwitchId":"vsw-2zed9txvy7h2srqo6****",
                "InstanceType":"ecs.n1.medium"
            }
        }
    },
    "Outputs":{
        "InstanceId":{
            "Value":{
                "Fn::GetAtt":[
                    "WebServer",
                    "InstanceId"
                ]
            }
        },
        "ZoneId":{
            "Value":{
                "Fn::GetAtt":[
                    "WebServer",
                    "ZoneId"
                ]
            }
        }
    }
}

Supported functions

  • Fn::Or
  • Fn::Not
  • Fn::Equals
  • Fn::FindInMap
  • Fn::And
  • Ref

Fn::ListMerge

The Fn::ListMerge function is used to merge multiple lists into one list.

Declaration 
{"Fn::ListMerge": [["list_1_item_1", "list_1_imte_2", ...], ["list_2_item_1", "list_2_imte_2", ...]]}
Parameters
  • ["list_1_item_1", "list_1_imte_2", ...]: the first list to merge.
  • ["list_2_item_1", "list_2_imte_2", ...]: the second list to merge into the first list.

Examples

The following example demonstrates how to attach two ECS instance groups to an SLB instance: 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Resources" : {
    "LoadBalancer": {
      "Type": "ALIYUN::SLB::LoadBalancer",
      "Properties": {
        "LoadBalancerName": "ros",
        "AddressType": "internet",
        "InternetChargeType": "paybybandwidth",
      }
    },
    "BackendServer1": {
      "Type": "ALIYUN::ECS::InstanceGroup",
      "Properties": {
        "ImageId" : "m-2ze9uqi7wo61hwep****",
        "InstanceType": "ecs.t1.small",
        "SecurityGroupId": "sg-2ze8yxgempcdsq3i****",
        "MaxAmount": 1,
        "MinAmount": 1
      }
    },
    "BackendServer2": {
      "Type": "ALIYUN::ECS::InstanceGroup",
      "Properties": {
        "ImageId" : "m-2ze9uqi7wo61hwep****",
        "InstanceType": "ecs.t1.small",
        "SecurityGroupId": "sg-2ze8yxgempcdsq3i****",
        "MaxAmount": 1,
        "MinAmount": 1
      }
    },
    "Attachment": {
      "Type": "ALIYUN::SLB::BackendServerAttachment",
      "Properties": {
        "LoadBalancerId": {"Ref": "LoadBalancer"},
        "BackendServerList": { "Fn::ListMerge": [
            {"Fn::GetAtt": ["BackendServer1", "InstanceIds"]},
            {"Fn::GetAtt": ["BackendServer2", "InstanceIds"]}
          ]
        }
      }
    }
  }
}

Supported functions

  • Fn::Base64Encode
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref
  • Fn::Join
  • Fn::If

Fn::GetJsonValue

The Fn::GetJsonValue function is used to resolve a JSON string and obtain its key value from the first layer.

Declaration 
{"Fn::GetJsonValue": ["key", "json_string"]}
Parameters
  • key: the key value.
  • json_string: the specified JSON string to be resolved.

Examples

In the following example, the WebServer instance executes UserData and returns a JSON string, and the WebServer2 instance then obtains the corresponding key value from the string. 
{
  "ROSTemplateFormatVersion" : "2015-09-01",
  "Resources" : {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId" : "m-2ze45uwova5fedlu****",
        "InstanceType": "ecs.n1.medium",
        "SecurityGroupId": "sg-2ze7pxymaix640qr****",
        "Password": "Wenqiao****",
        "IoOptimized": "optimized",
        "VSwitchId": "vsw-2zei67xd9nhcqxzec****",
        "VpcId": "vpc-2zevx9ios1rszqv0a****",
        "SystemDiskCategory": "cloud_ssd",
        "UserData": {"Fn::Join": ["", [
             "#! /bin/sh\n",
             "mkdir ~/test_ros\n",
             "print hello > ~/1.txt\n",
             "Fn::GetAtt": ["WaitConHandle", "CurlCli"],
             "\n",
             "Fn::GetAtt": ["WaitConHandle", "CurlCli"],
             " -d '{\\"id\\" : \\"1\\", \\"data\\": [\\"1111\\", \\"2222\\"]}'\n"
         ]]},
         "PrivateIpAddress": "192.168.XX.XX",
         "HostName": "userdata-1"
      }
    },
    "WaitConHandle": {
        "Type": "ALIYUN::ROS::WaitConditionHandle"
    },
    "WaitCondition": {
        "Type": "ALIYUN::ROS::WaitCondition",
        "Properties": {
          "Handle": {"Ref": "WaitConHandle"},
          "Timeout": 900
        }
    },
    "WebServer2": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "ImageId" : "m-2ze45uwova5fedlu****",
        "InstanceType": "ecs.n1.medium",
        "SecurityGroupId": "sg-2ze7pxymaix640qr****",
        "Password": "Wenqiao****",
        "IoOptimized": "optimized",
        "VSwitchId": "vsw-2zei67xd9nhcqxzec****",
        "VpcId": "vpc-2zevx9ios1rszqv0a****",
        "SystemDiskCategory": "cloud_ssd",
        "UserData":
          {"Fn::Join": ["", [
             "#! /bin/sh\n",
             "mkdir ~/test_ros\n",
             "echo hello > ~/1.txt\n",
             "server_1_token=",
             {"Fn::GetJsonValue": ["1", { "Fn::GetAtt": ["WaitCondition", "Data"]}]},
             "\n"
         ]]},
         "PrivateIpAddress": "192.168.XX.XX",
         "HostName": "userdata-2"
      }
    },
  },
  "Outputs": {
    "InstanceId": {
         "Value" : {"Fn::GetAtt": ["WebServer","InstanceId"]}
    },
    "PublicIp": {
         "Value" : {"Fn::GetAtt": ["WebServer","PublicIp"]}
    }
  }
}

Supported functions

  • Fn::Base64Encode
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref
  • Fn::Join
  • Fn::If

Fn::MergeMapToList

The Fn::MergeMapToList function is used to merge multiple mappings into a list of mapping elements.

Declaration

{"Fn::MergeMapToList": [{"key_1": ["key_1_item_1", "key_1_item_2", ...]}, {"key_2":["key_2_item_1", "key_2_item_2", ...]}, ... ]}
Parameters
  • {"key_1": ["key_1_item_1", "key_1_item_2", ...]}: the first mapping to merge. The " key_1" value must be a list. " key_1" is the key for each mapping in the list of merged mappings. The "key_1" value is "key_1_item_1" for the first merged mapping and "key_1_item_2" for the second merged mapping. All values follow the same format. The length of the final list of merged mappings is the length of the longest list "key_x" from all mappings being merged. If a "key_y" list is shorter, the last element of the list is repeated until the list is the longest.
  • {"key_2": ["key_2_item_1", "key_2_item_2", ...]}: the second mapping to merge into the first mapping. The " key_2" value must be a list. " key_2" is the key for each mapping in the merged list. The "key_2" value is "key_2_item_1" for the first merged mapping and "key_2_item_2" for the second merged mapping.
Examples
  • The following example demonstrates how to merge three mappings. The length of the list based on the key values for each mapping is the same. 
    {
   "Fn::MergeMapToList": [
      {"key_1": ["kye_1_item_1", "kye_1_item_2"]},
      {"key_2": ["kye_2_item_1", "kye_2_item_2"]},
      {"key_3": ["kye_3_item_1", "kye_3_item_2"]}
   ]
}
    The merged result is as follows: 
    [  
   {
      "key_1": "kye_1_item_1",
      "key_2": "kye_2_item_1",
      "key_3": "kye_3_item_1"
    },
    {
      "key_1": "kye_1_item_2",
      "key_2": "kye_2_item_2",
      "key_3": "kye_3_item_2"
    }
]
  • The length of the list based on the key values for each mapping varies in the following example: 
    {
   "Fn::MergeMapToList": [
      {"key_1": ["kye_1_item_1", "kye_1_item_2"]},
      {"key_2": ["kye_2_item_1", "kye_2_item_2", "key_2_item_3"]},
      {"key_3": ["kye_3_item_1", "kye_3_item_2"]}
   ]
}
    The merged result is as follows: 
    [  
   {
      "key_1": "kye_1_item_1", 
      "key_2": "kye_2_item_1",
      "key_3": "kye_3_item_1"
    },
    {
      "key_1": "kye_1_item_2", 
      "key_2": "kye_2_item_2",
      "key_3": "kye_3_item_2"
    },
    {
      "key_1": "kye_1_item_2", 
      "key_2": "kye_2_item_3",
      "key_3": "kye_3_item_2"
    }
]
  • In the following template example, all instances created in WebServer are added to the VServer group of an SLB instance: 
    {
    "ROSTemplateFormatVersion": "2015-09-01",
    "Resources": {
        "WebServer": {
          "Type": "ALIYUN::ECS::InstanceGroupClone",
          "Properties": {
              "SourceInstanceId": "i-xxxxx",
               "Password": "Hello****",
               "MinAmount": 1,
               "MaxAmount": 1
          }
        },
        "CreateVServerGroup": {
            "Type": "ALIYUN::SLB::VServerGroup",
            "Properties": {
                "LoadBalancerId": "lb-****",
                "VServerGroupName": "VServerGroup-****",
                "BackendServers": {
                   "Fn::MergeMapToList": [
                       {"Port": [6666, 9090, 8080]},
                       {"ServerId": {"Fn::GetAtt": ["WebServer", "InstanceIds"]}},
                       {"Weight": [20, 100]}
                   ]
                }
            }
        }
    }
}

Supported functions

  • Fn::Base64Encode
  • Fn::GetAtt
  • Fn::Join
  • Fn::Select
  • Ref
  • Fn::Join
  • Fn::If
  • Fn::ListMerge
  • Fn::GetJsonValue

Fn::Avg

The Fn::Avg function is used to return the average value of a set of numbers.

Declaration

{"Fn::Avg": [ndigits, [number1, number2, ... ]]}
Parameters
  • ndigits: the number of decimal places to report. This parameter value must be an integer.
  • [ number1, number2, ... ]: the set of numbers for which the average value will be calculated. Each element in the group must be either a number or a string that can be converted into a number.

Return value

The average value of the set of numbers.

Examples 
{ "Fn::Avg": [ 1, [1, 2, 6.0] ] } 
{ "Fn::Avg": [ 1, ['1', '2', '6.0'] ] }

3.0 is returned in this example.

Supported functions

  • Fn::GetAtt
  • Ref

Fn::SelectMapList

The Fn::SelectMapList function is used to return a list of map elements.

Declaration 
{"Fn::SelectMapList": ["key2", [{"key1": "value1-1", "key3": "value1-3"}, {"key1": "value2-1", "key2": "value2-2"}, {"key1": "value3-1", "key2": "value3-2"}, ...] ] }

Parameters

  • key2: the key to be queried in the map.
  • [{ "key1": "value1-1", "key3": "value1-3" }, ... ]: the list of maps.

Return value

A list of key values for all maps in the map list.

Examples 
{
 "Fn::SelectMapList": [
   "key2",
   [
      {"key1": "value1-1", "key3": "value1-3"},
      {"key1": "value2-1", "key2": "value2-2"},
      {"key1": "value3-1", "key2": "value3-2"}
   ]
 ]
}

["value2-2","value3-2"] is returned in this example.

Fn::Add

The Fn::Add function is used to sum the values of parameters.

Declaration 
{"Fn::Add": [{"Product": "ROS"}, {"Fn": "Add"}]}

Parameters

  • The parameters must be arranged as a list.
  • The parameters in the list can be of the Number, List, or Dictionary type. All the parameters must be of the same type. The list must contain at least two parameters.

Return value

If the parameter values are numbers, sum the parameter values. If the parameter values are lists, concatenate the values. If the parameter values are dictionaries, merge the values, and overwrite the former parameter value with the latter one if the two parameters have the same key.

Examples 
{
 "Fn::Add": [
   {"Product": "ROS"},
   {"Fn": "Add"}
 ]
}

{"Fn":"Add","Product":"ROS"} is returned in this example.

Fn::Calculate

The Fn::Calculate function is used to calculate an expression in string format.

Declaration 
 {"Fn::Calculate" : [expression, ndigits, [<number1>, <number2>, ... ]]}

Parameters

  • expression: the expression in string format.
  • ndigits: the number of decimal places to report. This parameter value must be 0 or an positive integer. This parameter takes effect only if the expression contains floating-point numbers.
  • [<number0>, <number1>, <number2>, ... ]: an optional parameter. You can define {n} in the expression, where n indicates the index of a specific number. You can replace {n} with the number while calculating the expression.

Return value

The calculation result of the expression.

Examples 
{"Fn::Calculate": ["(2+3)/2*3-1", 1]}  
{"Fn::Calculate": ["(2.0+3)/2*3-1", 1]}
{"Fn::Calculate": ["({1}+3)/2*3-1", 1, [3, 5, 6]]}
The calculation result is as follows: 
6
6.5
11

Fn::Sub

The Fn::Sub function substitutes variables in an input string by using values that you specify.

Declaration 
{ "Fn::Sub": [ String, { Var1Name: Var1Value, Var2Name: Var2Value, ... } ] }
Parameters
  • String

    A string with variables that ROS substitutes with specified values during runtime. Write variables in the ${VarName} format. Variables can be template parameter names, pseudo parameter names, resource logical IDs, resource attributes, or variables in key-value mappings. If you specify only template parameter names, pseudo parameter names, resource logical IDs, and resource attributes, you do not need to specify variables in key-value mappings.

    If you specify template parameter names, pseudo parameter names, or resource logical IDs, such as ${MyParameter}, ROS returns the same values as if you used the Ref built-in function. If you specify resource attributes such as ${MyInstance.InstanceId}, ROS returns the same values as if you used the Fn::GetAtt built-in function.

    To use the combination of ${} as normal characters without being escaped, add an exclamation point (!) after the open brace, such as ${! Literal}. ROS resolves this text as ${Literal}.

  • VarName

    The name of a variable that you included in the String parameter.

  • VarValue

    The value that ROS substitutes for the associated variable name during runtime.

If key-value mappings are not required, you can use the following declaration: 
{ "Fn::Sub": String }

Return value

ROS returns the substituting string and substitute the values of all variables.

Examples 
{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "VpcName": {
      "Type": "String",
      "Default": "vpc"
    }
  },
  "Resources": {
    "Vpc": {
      "Type": "ALIYUN::ECS::VPC",
      "Properties": {
        "VpcName": {
          "Ref": "VpcName"
        },
        "CidrBlock": "10.0.XX.XX"
      }
    }
  },
  "Outputs": {
    "Pseudo": {
      "Value": {
        "Fn::Sub": [
          "Var1: ${Var1}, Var2: ${Var2}, StackName: ${ALIYUN::StackName}, Region: ${ALIYUN::Region}",
          {
            "Var1": "Var1Value",
            "Var2": "Var2Value"
          }
        ]
      }
    },
    "VpcId": {
      "Value": {
        "Fn::Sub": "Return value of the resource: ${Vpc.VpcId}. Resource ID: ${Vpc}".
      }
    }
  }
}
In this example, the following values are returned: 
Var1: Var1Value, Var2: Var2Value, StackName: SubTest, Region: cn-hangzhou
Return value of the resource: vpc-bp11eu7avmtvr37hl****. Resource ID: vpc-bp11eu7avmtvr37hl****.