cfn-init - AWS CloudFormation
SyntaxOptionsExamplesRelated resources

cfn-init

In a CloudFormation template, you can use AWS::CloudFormation::Init within the Metadata section of an Amazon EC2 resource to define initialization tasks. For more information, see AWS::CloudFormation::Init in the AWS CloudFormation User Guide.

The cfn-init helper script reads template metadata from the AWS::CloudFormation::Init key and acts accordingly to:

  • Fetch and parse metadata from CloudFormation

  • Install packages

  • Write files to disk

  • Enable/disable and start/stop services

The cfn-init helper script is typically run from an Amazon EC2 instance's or launch template's user data.

Note

If you use cfn-init to update an existing file, it creates a backup copy of the original file in the same directory with a .bak extension. For example, if you update /path/to/file_name, the action produces two files: /path/to/file_name.bak contains the original file's contents and /path/to/file_name contains the updated contents.

Syntax

cfn-init --stack|-s stack.name.or.id \
         --resource|-r logical.resource.id \
         --region region \
         --access-key access.key \
         --secret-key secret.key \
         --role rolename \
         --credential-file|-f credential.file \
         --configsets|-c config.sets \
         --url|-u service.url \
         --http-proxy HTTP.proxy \
         --https-proxy HTTPS.proxy \
         --verbose|-v
Note

cfn-init 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.

Options

Name Description Required

-s, --stack

Stack name or stack ID.

Type: String

Default: None

Example: --stack { "Ref" : "AWS::StackName" },

Yes

-r, --resource

The logical resource ID of the resource that contains the metadata.

Type: String

Example: --resource WebServerHost

Yes

--region

The CloudFormation regional endpoint to use.

Type: String

Default: us-east-1

Example:--region ", { "Ref" : "AWS::Region" },

No

--access-key

AWS access key for an account with permission to call DescribeStackResource on CloudFormation. The credential file parameter supersedes this parameter.

Type: String

No

--secret-key

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

Type: String

No

--role

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

Type: String

Condition: The credential file parameter supersedes this parameter.

No

-f, --credential-file

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

-c, --configsets

A comma-separated list of configsets to run (in order).

Type: String

Default: default

No

-u, --url

The CloudFormation endpoint to use.

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

-v, --verbose

Verbose output. This is useful for debugging cases where cfn-init is failing to initialize.

Note

To debug initialization events, you should turn DisableRollback on. You can then SSH into the console and read the logs at /var/log/cfn-init.log. For more information, see Choose how to handle failures when provisioning resources in the AWS CloudFormation User Guide.

No

-h, --help

Shows the help message and exits.

No

Examples

Amazon Linux examples

The following examples show the UserData property of an EC2 instance, which runs the InstallAndRun configset that's associated with the WebServerInstance resource.

To include the latest version, add yum install -y aws-cfn-bootstrap to the UserData.

JSON

UserData property using the Fn::Join intrinsic function.

{
    "UserData": {
        "Fn::Base64": {
            "Fn::Join": [
                "",
                [
                    "#!/bin/bash -xe\n",
                    "",
                    "yum install -y aws-cfn-bootstrap",
                    "/opt/aws/bin/cfn-init -v ",
                    "         --stack ",
                    {
                        "Ref": "AWS::StackName"
                    },
                    "         --resource WebServerInstance ",
                    "         --configsets InstallAndRun ",
                    "         --region ",
                    {
                        "Ref": "AWS::Region"
                    },
                    "\n"
                ]
            ]
        }
    }
}

YAML

UserData property using the Fn::Join intrinsic function.

UserData: !Base64 
  'Fn::Join':
    - ''
    - - |
        #!/bin/bash -xe
      - ''
      - yum install -y aws-cfn-bootstrap
      - '/opt/aws/bin/cfn-init -v '
      - '         --stack '
      - !Ref 'AWS::StackName'
      - '         --resource WebServerInstance '
      - '         --configsets InstallAndRun '
      - '         --region '
      - !Ref 'AWS::Region'
      - |+

JSON

UserData property using the Fn::Sub intrinsic function.

{
    "UserData": {
        "Fn::Base64": {
            "Fn::Sub": [
                "#!/bin/bash -x\n# Install the files and packages from the metadata\n/opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource MyInstance --region ${AWS::Region}\n\n# Signal the status from cfn-init\n/opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource MyInstance --region ${AWS::Region}\n",
                {}
            ]
        }
    }
}

YAML

UserData property using the Fn::Sub intrinsic function.

UserData: !Base64 
  'Fn::Sub':
    - >
      #!/bin/bash -x

      # Install the files and packages from the metadata

      /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource MyInstance
      --region ${AWS::Region}


      # Signal the status from cfn-init

      /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource
      MyInstance --region ${AWS::Region}
    - {}

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

For Windows templates, see Working with Microsoft Windows stack templates in the AWS CloudFormation User Guide.