cfn-init

Description

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

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.

For information about the template metadata, see AWS::CloudFormation::Init.

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.

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 

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 do this by using the CloudFormation console, selecting Show Advanced Options, and then setting Rollback on failure to No. You can then SSH into the console and read the logs at /var/log/cfn-init.log.	No
-h, --help	Shows the help message and exits.	No

Example

Amazon Linux example

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

For a complete example template, see Deploying applications on Amazon EC2 with AWS CloudFormation.

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}
    - {}