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Showing content from https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-init.html below:

AWS::CloudFormation::Init - AWS CloudFormation

AWS::CloudFormation::Init

Use the AWS::CloudFormation::Init type to include metadata on an Amazon EC2 instance for the cfn-init helper script. If your template calls the cfn-init script, the script looks for resource metadata rooted in the AWS::CloudFormation::Init metadata key. For more information, see cfn-init.

cfn-init supports all metadata types for Linux systems. It supports metadata types for Windows with conditions that are described in the sections that follow.

Syntax

The configuration is separated into sections. The following template snippet shows how you can attach metadata for cfn-init to an EC2 instance resource within the template.

The metadata is organized into config keys, which you can group into configsets. You can specify a configset when you call cfn-init in your template. If you don't specify a configset, cfn-init looks for a single config key named config.

Note

The cfn-init helper script processes these configuration sections in the following order: packages, groups, users, sources, files, commands, and then services. If you require a different order, separate your sections into different config keys, and then use a configset that specifies the order in which the config keys should be processed.

JSON

"Resources": {
  "MyInstance": {
    "Type": "AWS::EC2::Instance",
    "Metadata" : {
      "AWS::CloudFormation::Init" : {
        "config" : {
          "packages" : {
            :
          },
          "groups" : {
            :
          },
          "users" : {
            :
          },
          "sources" : {
            :
          },
          "files" : {
            :
          },
          "commands" : {
            :
          },
          "services" : {
            :
          }
        }
      }
    },
    "Properties": {
      :
    }
  }
}

YAML

Resources: 
  MyInstance: 
    Type: AWS::EC2::Instance
    Metadata: 
      AWS::CloudFormation::Init: 
        config: 
          packages: 
            :
          groups: 
            :
          users: 
            :
          sources: 
            :
          files: 
            :
          commands: 
            :
          services: 
            :
    Properties: 
      :

Note

The following sections contain examples for scripts written in Unix-like shell scripting languages, such as Bash. To create scripts for PowerShell instead, make sure you're familiar with the PowerShell language. PowerShell syntax is different from Unix-like shells, so you'll need to have familiarity with the PowerShell way of doing things.

Configsets

If you want to create more than one config key and to have cfn-init process them in a specific order, create a configset that contains the config keys in the desired order.

Single configset

The following template snippet creates configsets named ascending and descending that each contain two config keys.

JSON

"AWS::CloudFormation::Init" : {
    "configSets" : {
        "ascending" : [ "config1" , "config2" ],
        "descending" : [ "config2" , "config1" ]
    },
    "config1" : {
        "commands" : {
            "test" : {
                "command" : "echo \"$CFNTEST\" > test.txt",
                "env" : { "CFNTEST" : "I come from config1." },
                "cwd" : "~"
            }
        }
    },
    "config2" : {
        "commands" : {
            "test" : {
                "command" : "echo \"$CFNTEST\" > test.txt",
                "env" : { "CFNTEST" : "I come from config2" },
                "cwd" : "~"
            }
        }
    }
}

YAML

AWS::CloudFormation::Init: 
  configSets: 
    ascending: 
      - "config1"
      - "config2"
    descending: 
      - "config2"
      - "config1"
  config1: 
    commands: 
      test: 
        command: "echo \"$CFNTEST\" > test.txt"
        env: 
          CFNTEST: "I come from config1."
        cwd: "~"
  config2: 
    commands: 
      test: 
        command: "echo \"$CFNTEST\" > test.txt"
        env: 
          CFNTEST: "I come from config2"
        cwd: "~"

Related cfn-init calls

The following example calls to cfn-init refer to the preceding example configsets. The example calls are abbreviated for clarity. See cfn-init for the complete syntax.

If a call to cfn-init specifies the ascending configset:
```
cfn-init -c ascending
```
The script processes config1 and then processes config2 and the test.txt file would contain the text I come from config2.
If a call to cfn-init specifies the descending configset:
```
cfn-init -c descending
```
The script processes config2 and then processes config1 and the test.txt file would contain the text I come from config1.

Multiple configsets

You can create multiple configsets, and call a series of them using your cfn-init script. Each configset can contain a list of config keys or references to other configsets. For example, the following template snippet creates three configsets. The first configset, test1, contains one config key named 1. The second configset, test2, contains a reference to the test1 configset and one config key named 2. The third configset, default, contains a reference to the configset test2.

JSON

"AWS::CloudFormation::Init" : {
    "configSets" : {
        "test1" : [ "1" ],
        "test2" : [ { "ConfigSet" : "test1" }, "2" ],
        "default" : [ { "ConfigSet" : "test2" } ]
    },
    "1" : {
        "commands" : {
            "test" : {
                "command" : "echo \"$MAGIC\" > test.txt",
                "env" : { "MAGIC" : "I come from the environment!" },
                "cwd" : "~"
            }
        }
    },
    "2" : {
        "commands" : {
            "test" : {
                "command" : "echo \"$MAGIC\" >> test.txt",
                "env" : { "MAGIC" : "I am test 2!" },
                "cwd" : "~"
            }
        }
    }
}

YAML

AWS::CloudFormation::Init:
  1:
    commands:
      test:
        command: "echo \"$MAGIC\" > test.txt"
        env:
          MAGIC: "I come from the environment!"
        cwd: "~"
  2:
    commands:
      test:
        command: "echo \"$MAGIC\" >> test.txt"
        env:
          MAGIC: "I am test 2!"
        cwd: "~"
  configSets: 
    test1:
      - "1"
    test2:
      - ConfigSet: "test1"
      - "2"
    default:
      - ConfigSet: "test2"

Related cfn-init calls

The following calls to cfn-init refer to the configSets declared in the preceding template snippet. The example calls are abbreviated for clarity. See cfn-init for the complete syntax.

If you specify test1 only:
```
cfn-init -c test1
```
cfn-init processes config key 1 only.
If you specify test2 only:
```
cfn-init -c test2
```
cfn-init processes config key 1 and then processes config key 2.
If you specify the default configset (or no configsets at all):
```
cfn-init -c default
```
You'll get the same behavior that you would if you specify configset test2.

Commands

You can use the commands key to run commands on the EC2 instance. The commands are processed in alphabetical order by name.

Key Required Description

command

Required

Either an array or a string specifying the command to run. If you use an array, you don't need to escape space characters or enclose command parameters in quotes. Don't use the array to specify multiple commands.

env

Optional

Sets environment variables for the command. This property overwrites, rather than appends, the existing environment.

cwd

Optional

The working directory.

test

Optional

A test command that determines whether cfn-init runs commands that are specified in the command key. If the test passes, cfn-init runs the commands. The cfn-init script runs the test in a command interpreter, such as Bash or cmd.exe. Whether a test passes depends on the exit code that the interpreter returns.

For Linux, the test command must return an exit code of 0 for the test to pass. For Windows, the test command must return an %ERRORLEVEL% of 0.

ignoreErrors

Optional

A Boolean value that determines whether cfn-init continues to run if the command contained in the command key fails (returns a non-zero value). Set to true if you want cfn-init to continue running even if the command fails. Set to false if you want cfn-init to stop running if the command fails. The default value is false.

waitAfterCompletion

Optional

For Windows systems only. Specifies how long to wait (in seconds) after a command has finished in case the command causes a reboot. The default value is 60 seconds and a value of "forever" directs cfn-init to exit and resume only after the reboot is complete. Set this value to 0 if you don't want to wait for every command.

Example

The following example snippet calls the echo command if the ~/test.txt file doesn't exist.

JSON

"commands" : {
    "test" : {
        "command" : "echo \"$MAGIC\" > test.txt",
        "env" : { "MAGIC" : "I come from the environment!" },
        "cwd" : "~",
        "test" : "test ! -e ~/test.txt",
        "ignoreErrors" : "false"
    },
    "test2" : {
        "command" : "echo \"$MAGIC2\" > test2.txt",
        "env" : { "MAGIC2" : "I come from the environment!" },
        "cwd" : "~",
        "test" : "test ! -e ~/test2.txt",
        "ignoreErrors" : "false"
    }
}

YAML

commands:
  test:
    command: "echo \"$MAGIC\" > test.txt"
    env:
      MAGIC: "I come from the environment!"
    cwd: "~"
    test: "test ! -e ~/test.txt"
    ignoreErrors: "false"
  test2:
    command: "echo \"$MAGIC2\" > test2.txt"
    env:
      MAGIC2: "I come from the environment!"
    cwd: "~"
    test: "test ! -e ~/test2.txt"
    ignoreErrors: "false"

Files

You can use the files key to create files on the EC2 instance. The content can be either inline in the template or the content can be pulled from a URL. The files are written to disk in lexicographic order. The following table lists the supported keys.

Key Description

content

Either a string or a properly formatted JSON object. If you use a JSON object as your content, the JSON will be written to a file on disk. Any intrinsic functions such as Fn::GetAtt or Ref are evaluated before the JSON object is written to disk. When you create a symlink, specify the symlink target as the content.

Note

If you create a symlink, the helper script modifies the permissions of the target file. Currently, you can't create a symlink without modifying the permissions of the target file.

source

A URL to load the file from. This option can't be specified with the content key.

encoding

The encoding format. Only used if the content is a string. Encoding isn't applied if you are using a source.

Valid values: plain | base64

group

The name of the owning group for this file. Not supported for Windows systems.

owner

The name of the owning user for this file. Not supported for Windows systems.

mode

A six-digit octal value representing the mode for this file. Not supported for Windows systems. Use the first three digits for symlinks and the last three digits for setting permissions. To create a symlink, specify 120xxx, where xxx defines the permissions of the target file. To specify permissions for a file, use the last three digits, such as 000644.

authentication

The name of an authentication method to use. This overrides any default authentication. You can use this property to select an authentication method you define with the AWS::CloudFormation::Authentication resource.

context

Specifies a context for files that are to be processed as Mustache templates. To use this key, you must have installed aws-cfn-bootstrap 1.3 â11 or later in addition to pystache.

Examples

The following example snippet creates a file named setup.mysql as part of a larger installation.

JSON

"files" : {
  "/tmp/setup.mysql" : {
    "content" : { "Fn::Join" : ["", [
      "CREATE DATABASE ", { "Ref" : "DBName" }, ";\n",
      "CREATE USER '", { "Ref" : "DBUsername" }, "'@'localhost' IDENTIFIED BY '",
                       { "Ref" : "DBPassword" }, "';\n",
      "GRANT ALL ON ", { "Ref" : "DBName" }, ".* TO '", { "Ref" : "DBUsername" },
                       "'@'localhost';\n",
      "FLUSH PRIVILEGES;\n"
      ]]},
    "mode"  : "000644",
    "owner" : "root",
    "group" : "root"
  }
}

YAML

files: 
  /tmp/setup.mysql: 
    content: !Sub |
      CREATE DATABASE ${DBName};
      CREATE USER '${DBUsername}'@'localhost' IDENTIFIED BY '${DBPassword}';
      GRANT ALL ON ${DBName}.* TO '${DBUsername}'@'localhost';
      FLUSH PRIVILEGES;
    mode: "000644"
    owner: "root"
    group: "root"

The full template is available at: https://s3.amazonaws.com/cloudformation-templates-us-east-1/Drupal_Single_Instance.template.

The following example snippet creates a symlink /tmp/myfile2.txt that points at an existing file /tmp/myfile1.txt. The permissions of the target file /tmp/myfile1.txt is defined by the mode value 644.

JSON

"files" : {
  "/tmp/myfile2.txt" : {
    "content" : "/tmp/myfile1.txt",
    "mode" : "120644"
  }
}

YAML

files:
  /tmp/myfile2.txt:
    content: "/tmp/myfile1.txt"
    mode: "120644"

Mustache templates are used primarily to create configuration files. For example, you can store a configuration file in an S3 bucket and interpolate Refs and GetAtts from the template, instead of using Fn::Join. The following example snippet outputs Content for test9 to /tmp/test9.txt.

JSON


"files" : {
    "/tmp/test9.txt" : {
        "content" : "Content for {{name}}",
        "context" : { "name" : "test9" }
    }
}

YAML

files:
  /tmp/test9.txt:
    content: "Content for {{name}}"
    context:
      name: "test9"

When working with Mustache templates, note the following:

The context key must be present for the files to be processed.
The context key must be a key-value map, but it can be nested.
You can process files with inline content by using the content key and remote files by using the source key.
Mustache support depends on the pystache version. Version 0.5.2 supports the Mustache 1.1.2 specification.

Groups

You can use the groups key to create Linux/UNIX groups and to assign group IDs. The groups key isn't supported for Windows systems.

To create a group, add a new key-value pair that maps a new group name to an optional group ID. The groups key can contain one or more group names. The following table lists the available keys.

Key Description

gid

A group ID number.

If a group ID is specified, and the group already exists by name, the group creation will fail. If another group has the specified group ID, the OS may reject the group creation.

Example: { "gid" : "23" }

Example snippet

The following snippet specifies a group named groupOne without assigning a group ID and a group named groupTwo that specified a group ID value of 45.

JSON

"groups" : {
    "groupOne" : {},
    "groupTwo" : { "gid" : "45" }
}

YAML

groups:
  groupOne: {}
  groupTwo:
    gid: "45"

Packages

You can use the packages key to download and install pre-packaged applications and components. On Windows systems, the packages key supports only the MSI installer.

Supported package formats

The cfn-init script currently supports the following package formats: apt, msi, python, rpm, rubygems, yum, and Zypper. Packages are processed in the following order: rpm, yum/apt/zypper, and then rubygems and python. There is no ordering between rubygems and python, and packages within each package manager aren't guaranteed to be installed in any order.

Specifying versions

Within each package manager, each package is specified as a package name and a list of versions. The version can be a string, a list of versions, or an empty string or list. An empty string or list indicates that you want the latest version. For rpm manager, the version is specified as a path to a file on disk or a URL.

If you specify a version of a package, cfn-init will attempt to install that version even if a newer version of the package is already installed on the instance. Some package managers support multiple versions, but others may not. Verify the documentation for your package manager for more information. If you don't specify a version and a version of the package is already installed, the cfn-init script won't install a new versionâ it will assume that you want to keep and use the existing version.

Example snippets RPM, yum, Rubygems, and Zypper

The following snippet specifies a version URL for rpm, requests the latest versions from yum and Zypper, and version 0.10.2 of chef from rubygems:

JSON

"rpm" : {
  "epel" : "http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm"
},
"yum" : {
  "httpd" : [],
  "php" : [],
  "wordpress" : []
},
"rubygems" : {
  "chef" : [ "0.10.2" ]
},
"zypper" : {
  "git" : []
}

YAML

rpm:
  epel: "http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm"
yum:
  httpd: []
  php: []
  wordpress: []
rubygems:
  chef:
    - "0.10.2"
zypper:
  git: []

MSI package

The following snippet specifies a URL for an MSI package:

JSON

"msi" : {
  "awscli" : "https://s3.amazonaws.com/aws-cli/AWSCLI64.msi"
}

YAML

msi:
  awscli: "https://s3.amazonaws.com/aws-cli/AWSCLI64.msi"

Services

You can use the services key to define which services should be enabled or disabled when the instance is launched. Amazon Linux 2 systems and above running aws-cfn-bootstrap version 2.0-29+ support this key by using systemd. Other Linux systems support this key using sysvinit (by default) or systemd (by adding the necessary configurations below). Windows systems support this key through Windows Service Manager.

The services key also allows you to specify dependencies on sources, packages, and files so that if a restart is needed due to files being installed, cfn-init will take care of the service restart. For example, if you download the Apache HTTP Server package, the package installation will automatically start the Apache HTTP Server during the stack creation process. However, if the Apache HTTP Server configuration is updated later in the stack creation process, the update won't take effect unless the Apache server is restarted. You can use the services key to ensure that the Apache HTTP service is restarted.

The following table lists the supported keys.

Key Description

ensureRunning

Set to true to ensure that the service is running after cfn-init finishes.

Set to false to ensure that the service isn't running after cfn-init finishes.

Omit this key to make no changes to the service state.

enabled

Set to true to ensure that the service will be started automatically upon boot.

Set to false to ensure that the service won't be started automatically upon boot.

Omit this key to make no changes to this property.

files

A list of files. If cfn-init changes one directly through the files block, this service will be restarted.

sources

A list of directories. If cfn-init expands an archive into one of these directories, this service will be restarted.

packages

A map of package manager to list of package names. If cfn-init installs or updates one of these packages, this service will be restarted.

commands

A list of command names. If cfn-init runs the specified command, this service will be restarted.

Examples Linux

The following Linux snippet configures the services as follows:

The nginx service will be restarted if either /etc/nginx/nginx.conf or /var/www/html are modified by cfn-init.
The php-fastcgi service will be restarted if cfn-init installs or updates php or spawn-fcgi using yum.
The sendmail service will be stopped and disabled using systemd.

JSON

"services" : {
  "sysvinit" : {
    "nginx" : {
      "enabled" : "true",
      "ensureRunning" : "true",
      "files" : ["/etc/nginx/nginx.conf"],
      "sources" : ["/var/www/html"]
    },
    "php-fastcgi" : {
      "enabled" : "true",
      "ensureRunning" : "true",
      "packages" : { "yum" : ["php", "spawn-fcgi"] }
    }
  },
  "systemd": {
    "sendmail" : {
      "enabled" : "false",
      "ensureRunning" : "false"
    }
  }
}

YAML

services:
  sysvinit:
    nginx:
      enabled: "true"
      ensureRunning: "true"
      files:
        - "/etc/nginx/nginx.conf"
      sources:
        - "/var/www/html"
    php-fastcgi:
      enabled: "true"
      ensureRunning: "true"
      packages:
        yum:
          - "php"
          - "spawn-fcgi"
  systemd:
    sendmail:
      enabled: "false"
      ensureRunning: "false"

To use systemd with a service, the service must have a systemd unit file configured. The following unit file allows systemd to start and stop the cfn-hup daemon in the multi-user service target:

[Unit]
Description=cfn-hup daemon
[Service]
ExecStart=/usr/bin/cfn-hup -v
PIDFile=/var/run/cfn-hup.pid
[Install]
WantedBy=multi-user.target

This configuration assumes that cfn-hup is installed under the /usr/bin directory. However, the actual location where cfn-hup is installed might vary on different platforms. You can override this configuration by creating an override file in /etc/systemd/system/cfn-hup.service.d/override.conf as follows:

# In this example, cfn-hup executable is available under /usr/local/bin
[Service]
ExecStart=
ExecStart=/usr/local/bin/cfn-hup -v

Windows

The following Windows snippet starts the cfn-hup service, sets it to automatic, and restarts the service if cfn-init modifies the specified configuration files:

JSON

"services" : {
  "windows" : {
    "cfn-hup" : {
      "enabled" : "true",
      "ensureRunning" : "true",
      "files" : ["c:\\cfn\\cfn-hup.conf", "c:\\cfn\\hooks.d\\cfn-auto-reloader.conf"]
    }
  }
}

YAML

services:
  windows:
    cfn-hup:
      enabled: "true"
      ensureRunning: "true"
      files:
        - "c:\\cfn\\cfn-hup.conf"
        - "c:\\cfn\\hooks.d\\cfn-auto-reloader.conf"

Sources

You can use the sources key to download an archive file and unpack it in a target directory on the EC2 instance. This key is fully supported for both Linux and Windows systems.

Supported formats

Supported formats are:

Examples GitHub

If you use GitHub as a source control system, you can use cfn-init and the sources package mechanism to pull a specific version of your application. GitHub allows you to create a .zip or a .tar from a specific version through a URL as follows:

https://github.com/<your directory>/(zipball|tarball)/<version>

For example, the following snippet pulls down version main as a .tar file.

JSON

"sources" : {
  "/etc/puppet" : "https://github.com/user1/cfn-demo/tarball/main"
  }

YAML

sources:
  /etc/puppet: "https://github.com/user1/cfn-demo/tarball/main"

S3 Bucket

The following example downloads a tarball from an S3 bucket and unpacks it into /etc/myapp:

JSON

"sources" : {
  "/etc/myapp" : "https://s3.amazonaws.com/amzn-s3-demo-bucket/myapp.tar.gz"
  }

YAML

sources:
  /etc/myapp: "https://s3.amazonaws.com/amzn-s3-demo-bucket/myapp.tar.gz"

Users

You can use the users key to create Linux/UNIX users on the EC2 instance. The users key isn't supported for Windows systems.

The following table lists the supported keys.

Key Description

uid

A user ID. The creation process fails if the user name exists with a different user ID. If the user ID is already assigned to an existing user the operating system may reject the creation request.

groups

A list of group names. The user will be added to each group in the list.

homeDir

The user's home directory.

Example

Users are created as non-interactive system users with a shell of /sbin/nologin. This is by design and can't be modified.

JSON

"users" : {
    "myUser" : {
        "groups" : ["groupOne", "groupTwo"],
        "uid" : "50",
        "homeDir" : "/tmp"
    }
}

YAML

users:
  myUser:
    groups:
      - "groupOne"
      - "groupTwo"
    uid: "50"
    homeDir: "/tmp"

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