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cfn\-init

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Description

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

• Fetch and parse metadata from AWS 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.

AWS::CloudFormation::Init

• Note*

cfn-init does not require credentials, so you do not need to use the `--access-key`, `--secret-key`, `--role`, or `--credential-file` options. However, if no credentials are specified, AWS 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` | Name of the Stack. *Type*: String *Default*: None *Example*: `-s { "Ref" : "AWS::StackName" },` | Yes |

| `-r, --resource ` | The logical resource ID of the resource that contains the metadata. *Type*: String *Example*: `-r WebServerHost` | Yes |

| `--region` | The AWS 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 AWS 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 is 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 AWS 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 output. This is useful for debugging cases where cfn-init is failing to initialize. To debug initialization events, you should turn DisableRollback on. You can do this by using the AWS 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 |

Example

Amazon Linux example

The following snippet shows the `UserData` property of an EC2 instance, which runs the `InstallAndRun` configset that is associated with the `WebServerInstance` resource.

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

Deploying applications on Amazon EC2 with AWS CloudFormation

JSON

"UserData" : { "Fn::Base64" :
  { "Fn::Join" : ["", [
     "#!/bin/bash -xe\n",
     "# Install the files and packages from the metadata\n",
     "/opt/aws/bin/cfn-init -v ",
     "         --stack ", { "Ref" : "AWS::StackName" },
     "         --resource WebServerInstance ",
     "         --configsets InstallAndRun ",
     "         --region ", { "Ref" : "AWS::Region" }, "\n"
  ]]}
}

YAML

UserData: !Base64 
  'Fn::Join':
    - ''
    - - |
        #!/bin/bash -xe
      - |
        # Install the files and packages from the metadata
      - '/opt/aws/bin/cfn-init -v '
      - '         --stack '
      - !Ref 'AWS::StackName'
      - '         --resource WebServerInstance '
      - '         --configsets InstallAndRun '
      - '         --region '
      - !Ref 'AWS::Region'
      - |+