Merge pull request #77 from chexxor/master
Update cloud-config.md to include expected file format
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Brian Waldon
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# Customize with Cloud-Config
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# Functionality Overview
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CoreOS allows you to configure networking, create users, launch systemd units on startup and more. We've designed our implementation to allow the same cloud-config file to work across all of our supported platforms.
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CoreOS allows you to declaratively customize various OS-level items, such as network configuration, user accounts, and systemd units. This document describes the full list of items we can configure. The `coreos-cloudinit` program uses these files as it configures the OS after startup or during runtime.
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Only a subset of [cloud-config functionality][cloud-config] is implemented. A set of custom parameters were added to the cloud-config format that are specific to CoreOS. An example file containing all available options can be found at the bottom of this page.
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# Configuration File
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The file used by this system initialization program is called a "cloud-config" file. It is inspired by the [cloud-init][cloud-init] project's [cloud-config][cloud-config] file. which is "the defacto multi-distribution package that handles early initialization of a cloud instance" ([cloud-init docs][cloud-init-docs]). Because the cloud-init project includes tools which aren't used by CoreOS, only the relevant subset of its configuration items will be implemented in our cloud-config file. In addition to those, we added a few CoreOS-specific items, such as etcd configuration, OEM definition, and systemd units.
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We've designed our implementation to allow the same cloud-config file to work across all of our supported platforms.
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[cloud-init]: https://launchpad.net/cloud-init
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[cloud-init-docs]: http://cloudinit.readthedocs.org/en/latest/index.html
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[cloud-config]: http://cloudinit.readthedocs.org/en/latest/topics/format.html#cloud-config-data
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## How to Provide Cloud-Config
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## File Format
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The cloud-config file uses the [YAML][yaml] file format, which uses whitespace and new-lines to delimit lists, associative arrays, and values.
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A cloud-config file should contain an associative array which has zero or more of the following keys:
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- `coreos`
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- `ssh_authorized_keys`
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- `hostname`
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- `users`
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- `write_files`
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- `manage_etc_hosts`
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The expected values for these keys are defined in the rest of this document.
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[yaml]: https://en.wikipedia.org/wiki/YAML
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## Providing Cloud-Config with Config-Drive
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CoreOS tries to conform to each platform's native method to provide user data. Each cloud provider tends to be unique, but this complexity has been abstracted by CoreOS. You can view each platform's instructions on their documentation pages. The most universal way to provide cloud-config is [via config-drive](https://github.com/coreos/coreos-cloudinit/blob/master/Documentation/config-drive.md), which attaches a read-only device to the machine, that contains your cloud-config file.
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# Configuration Parameters
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## CoreOS Parameters
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### coreos.etcd
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## `coreos`
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The `coreos.etcd.*` options are translated to a partial systemd unit acting as an etcd configuration file.
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### `etcd`
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The `coreos.etcd.*` parameters will be translated to a partial systemd unit acting as an etcd configuration file.
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We can use the templating feature of coreos-cloudinit to automate etcd configuration with the `$private_ipv4` and `$public_ipv4` fields. For example, the following cloud-config document...
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```
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@ -40,15 +67,14 @@ Environment="ETCD_ADDR=203.0.113.29:4001"
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Environment="ETCD_PEER_ADDR=192.0.2.13:7001"
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```
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For more information about the available configuration options, see the [etcd documentation][etcd-config].
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For more information about the available configuration parameters, see the [etcd documentation][etcd-config].
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Note that hyphens in the coreos.etcd.* keys are mapped to underscores.
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[etcd-config]: https://github.com/coreos/etcd/blob/master/Documentation/configuration.md
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### coreos.oem
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### `oem`
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These fields are borrowed from the [os-release spec][os-release] and repurposed
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as a way for coreos-cloudinit to know about the OEM partition on this machine:
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The `coreos.oem.*` parameters follow the [os-release spec][os-release], but have been repurposed as a way for coreos-cloudinit to know about the OEM partition on this machine:
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- **id**: Lowercase string identifying the OEM
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- **name**: Human-friendly string representing the OEM
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@ -84,10 +110,9 @@ BUG_REPORT_URL="https://github.com/coreos/coreos-overlay"
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[os-release]: http://www.freedesktop.org/software/systemd/man/os-release.html
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### coreos.units
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### `units`
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Arbitrary systemd units may be provided in the `coreos.units` attribute.
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`coreos.units` is a list of objects with the following fields:
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The `coreos.units.*` parameters define a list of arbitrary systemd units to start. Each item is an object with the following fields:
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- **name**: String representing unit's name. Required.
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- **runtime**: Boolean indicating whether or not to persist the unit across reboots. This is analagous to the `--runtime` argument to `systemd enable`. Default value is false.
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@ -135,14 +160,12 @@ coreos:
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command: start
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```
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## Cloud-Config Parameters
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## `ssh_authorized_keys`
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### ssh_authorized_keys
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Provided public SSH keys will be authorized for the `core` user.
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The `ssh_authorized_keys` parameter adds public SSH keys which will be authorized for the `core` user.
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The keys will be named "coreos-cloudinit" by default.
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Override this with the `--ssh-key-name` flag when calling `coreos-cloudinit`.
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Override this by using the `--ssh-key-name` flag when calling `coreos-cloudinit`.
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```
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#cloud-config
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@ -151,9 +174,9 @@ ssh_authorized_keys:
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- ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...
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```
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### hostname
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## `hostname`
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The provided value will be used to set the system's hostname.
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The `hostname` parameter defines the system's hostname.
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This is the local part of a fully-qualified domain name (i.e. `foo` in `foo.example.com`).
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```
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@ -162,10 +185,9 @@ This is the local part of a fully-qualified domain name (i.e. `foo` in `foo.exam
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hostname: coreos1
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```
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### users
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## `users`
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Add or modify users with the `users` directive by providing a list of user objects, each consisting of the following fields.
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Each field is optional and of type string unless otherwise noted.
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The `users` parameter adds or modifies the specified list of users. Each user is an object which consists of the following fields. Each field is optional and of type string unless otherwise noted.
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All but the `passwd` and `ssh-authorized-keys` fields will be ignored if the user already exists.
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- **name**: Required. Login name of user
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@ -203,7 +225,7 @@ users:
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- ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC0g+ZTxC7weoIJLUafOgrm+h...
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```
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#### Generating a password hash
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### Generating a password hash
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If you choose to use a password instead of an SSH key, generating a safe hash is extremely important to the security of your system. Simplified hashes like md5crypt are trivial to crack on modern GPU hardware. Here are a few ways to generate secure hashes:
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@ -223,9 +245,11 @@ perl -e 'print crypt("password","\$6\$SALT\$") . "\n"'
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Using a higher number of rounds will help create more secure passwords, but given enough time, password hashes can be reversed. On most RPM based distributions there is a tool called mkpasswd available in the `expect` package, but this does not handle "rounds" nor advanced hashing algorithms.
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#### Retrieving ssh authorized keys from a GitHub user
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### Retrieving SSH Authorized Keys
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Using the field `coreos-ssh-import-github` you can make coreos-cloudinit to add the public ssh keys from a GitHub user as authorized keys to a server.
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#### From a GitHub User
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Using the `coreos-ssh-import-github` field, we can import public SSH keys from a GitHub user to use as authorized keys to a server.
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```
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#cloud-config
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@ -235,10 +259,10 @@ users:
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coreos-ssh-import-github: elroy
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```
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#### Retrieving ssh authorized keys from an http endpoint
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#### From an HTTP Endpoint
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coreos-cloudinit can also pull public SSH keys from any http endpoint that matches [GitHub's API response format](https://developer.github.com/v3/users/keys/#list-public-keys-for-a-user).
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For example, if you have an installation of GitHub Enterprise, you can provide a complete url with an authentication token:
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We can also pull public SSH keys from any HTTP endpoint which matches [GitHub's API response format](https://developer.github.com/v3/users/keys/#list-public-keys-for-a-user).
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For example, if you have an installation of GitHub Enterprise, you can provide a complete URL with an authentication token:
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```
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#cloud-config
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@ -248,7 +272,7 @@ users:
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coreos-ssh-import-url: https://token:<OAUTH-TOKEN>@github-enterprise.example.com/users/elroy/keys
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```
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You can also provide any url which response matches that json format for public keys:
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You can also specify any URL whose response matches the JSON format for public keys:
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```
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#cloud-config
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@ -258,10 +282,9 @@ users:
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coreos-ssh-import-url: https://example.com/public-keys
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```
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### write_files
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## `write_files`
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Inject an arbitrary set of files to the local filesystem.
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Provide a list of objects with the following attributes:
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The `write-file` parameter defines a list of files to create on the local filesystem. Each file is represented as an associative array which has the following keys:
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- **path**: Absolute location on disk where contents should be written
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- **content**: Data to write at the provided `path`
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@ -271,10 +294,10 @@ Provide a list of objects with the following attributes:
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Explicitly not implemented is the **encoding** attribute.
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The **content** field must represent exactly what should be written to disk.
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### manage_etc_hosts
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## `manage_etc_hosts`
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Have coreos-cloudinit manage your /etc/hosts file for local name resolution.
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The only supported value is "localhost" which will cause your system's hostname
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The `manage_etc_hosts` parameter configures the contents of the `/etc/hosts` file, which is used for local name resolution.
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Currently, the only supported value is "localhost" which will cause your system's hostname
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to resolve to "127.0.0.1". This is helpful when the host does not have DNS
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infrastructure in place to resolve its own hostname, for example, when using Vagrant.
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