cfn-signal - AWS CloudFormation
Syntax for resource signaling (recommended)Syntax for use with wait condition handleOptionsExamplesRelated resources

cfn-signal

The cfn-signal helper script signals CloudFormation to indicate whether Amazon EC2 instances have been successfully created or updated. If you install and configure software applications on instances, you can signal CloudFormation when those software applications are ready.

You use the cfn-signal script in conjunction with a CreationPolicy attribute or an UpdatePolicy attribute with WaitOnResourceSignals for Amazon EC2 Auto Scaling groups. When CloudFormation creates or updates resources with those policies, it suspends work on the stack until the resource receives the required number of signals or until the timeout period is exceeded. For each valid signal that CloudFormation receives, it publishes the signals to the stack events so that you track each signal.

Syntax for resource signaling (recommended)

If you want to signal CloudFormation resources, use the following syntax.

cfn-signal --success|-s signal.to.send \
        --access-key access.key \
        --credential-file|-f credential.file \
        --exit-code|-e exit.code \
        --http-proxy HTTP.proxy \
        --https-proxy HTTPS.proxy \
        --id|-i unique.id \
        --region AWS.region \
        --resource resource.logical.ID \
        --role IAM.role.name \
        --secret-key secret.key \
        --stack stack.name.or.stack.ID \
        --url AWS CloudFormation.endpoint
Note

cfn-signal doesn't require credentials, so you don't need to use the --access-key, --secret-key, --role, or --credential-file options. However, if no credentials are specified, CloudFormation checks for stack membership and limits the scope of the call to the stack that the instance belongs to. For more information, see Permissions for helper scripts.

Syntax for use with wait condition handle

If you want to signal a wait condition handle, use the following syntax.

cfn-signal --success|-s signal.to.send \
        --reason|-r resource.status.reason \
        --data|-d data \
        --id|-i unique.id \
        --exit-code|-e exit.code \
        waitconditionhandle.url

Options

The options that you can use depend on whether you're signaling a creation policy or a wait condition handle. Some options that apply to a creation policy might not apply to a wait condition handle.

Name Description Required

--access-key (resource signaling only)

AWS access key for an account with permission to call the CloudFormation SignalResource API. The credential file parameter supersedes this parameter.

Type: String

No

-d, --data (wait condition handle only)

Data to send back with the waitConditionHandle. Defaults to blank.

Type: String

Default: blank

No

-e, --exit-code

The error code from a process that can be used to determine success or failure. If specified, the --success option is ignored.

Type: String

Examples: -e $? (for Linux), -e %ERRORLEVEL% (for Windows cmd.exe), and -e $lastexitcode (for Windows PowerShell).

No

-f, --credential-file (resource signaling only)

A file that contains both a secret access key and an access key. The credential file parameter supersedes the --role, --access-key, and --secret-key parameters.

Type: String

No

--http-proxy

An HTTP proxy (non-SSL). Use the following format: http://user:password@host:port

Type: String

No

--https-proxy

An HTTPS proxy. Use the following format: https://user:password@host:port

Type: String

No

-i, --id

The unique ID to send.

Type: String

Default: The ID of the Amazon EC2 instance. If the ID can't be resolved, the machine's Fully Qualified Domain Name (FQDN) is returned.

No

-r, --reason (wait condition handle only)

A status reason for the resource event (currently only used on failure) - defaults to 'Configuration failed' if success is false.

Type: String

No
--region (resource signaling only)

The CloudFormation regional endpoint to use.

Type: String

Default: us-east-1

No
--resource (resource signaling only)

The logical ID of the resource that contains the creations policy you want to signal.

Type: String

Yes

--role (resource signaling only)

The name of an IAM role that's associated with the instance.

Type: String

Condition: The credential file parameter supersedes this parameter.

No

-s, --success

If true, signal SUCCESS, else FAILURE.

Type: Boolean

Default: true

No

--secret-key (resource signaling only)

AWS secret access key that corresponds to the specified AWS access key.

Type: String

No

--stack (resource signaling only)

The stack name or stack ID that contains the resource you want to signal.

Type: String

Yes
-u, --url (resource signaling only)

The CloudFormation endpoint to use.

Type: String

No

waitconditionhandle.url (wait condition handle only)

A presigned URL that you can use to signal success or failure to an associated WaitCondition

Type: String

Yes

Examples

Amazon Linux example

A common usage pattern is to use cfn-init and cfn-signal together. The cfn-signal call uses the return status of the call to cfn-init (using the $? shell construct). If the application fails to install, the instance will fail to create and the stack will rollback.

JSON

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "Simple EC2 instance",
    "Resources": {
        "MyInstance": {
            "Type": "AWS::EC2::Instance",
            "Metadata": {
                "AWS::CloudFormation::Init": {
                    "config": {
                        "files": {
                            "/tmp/test.txt": {
                                "content": "Hello world!",
                                "mode": "000755",
                                "owner": "root",
                                "group": "root"
                            }
                        }
                    }
                }
            },
            "Properties": {
                "ImageId": "{{resolve:ssm:/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2}}",
                "InstanceType": "t2.micro",
                "UserData": {
                    "Fn::Base64": {
                        "Fn::Join": [
                            "",
                            [
                                "#!/bin/bash -x\n",
                                "# Install the files and packages from the metadata\n",
                                "yum install -y aws-cfn-bootstrap",
                                "\n",
                                "/opt/aws/bin/cfn-init -v ",
                                "         --stack ",
                                {
                                    "Ref": "AWS::StackName"
                                },
                                "         --resource MyInstance ",
                                "         --region ",
                                {
                                    "Ref": "AWS::Region"
                                },
                                "\n",
                                "# Signal the status from cfn-init\n",
                                "/opt/aws/bin/cfn-signal -e $? ",
                                "         --stack ",
                                {
                                    "Ref": "AWS::StackName"
                                },
                                "         --resource MyInstance ",
                                "         --region ",
                                {
                                    "Ref": "AWS::Region"
                                },
                                "\n"
                            ]
                        ]
                    }
                }
            },
            "CreationPolicy": {
                "ResourceSignal": {
                    "Timeout": "PT5M"
                }
            }
        }
    }
}

YAML

AWSTemplateFormatVersion: 2010-09-09
Description: Simple EC2 instance
Resources:
  MyInstance:
    Type: 'AWS::EC2::Instance'
    Metadata:
      'AWS::CloudFormation::Init':
        config:
          files:
            /tmp/test.txt:
              content: Hello world!
              mode: '000755'
              owner: root
              group: root
    Properties:
      ImageId: {{resolve:ssm:/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2}}
      InstanceType: t2.micro
      UserData: !Base64 
        'Fn::Join':
          - ''
          - - |
              #!/bin/bash -x
            - |
              # Install the files and packages from the metadata
            - yum install -y aws-cfn-bootstrap
            - |+
            
            - |
            - '/opt/aws/bin/cfn-init -v '
            - '         --stack '
            - !Ref 'AWS::StackName'
            - '         --resource MyInstance '
            - '         --region '
            - !Ref 'AWS::Region'
            - |+

            - |
              # Signal the status from cfn-init
            - '/opt/aws/bin/cfn-signal -e $? '
            - '         --stack '
            - !Ref 'AWS::StackName'
            - '         --resource MyInstance '
            - '         --region '
            - !Ref 'AWS::Region'
            - |+

    CreationPolicy:
      ResourceSignal:
        Timeout: PT5M

You can also visit our GitHub repository to download sample templates that use cfn-signal, including the following templates.