Create reference documentation for base config

Also add schema entries for the base config modules lists that can be
overridden with user data.

15 files changed, 533 insertions, 26 deletions

diff --git a/cloudinit/config/schemas/schema-cloud-config-v1.json b/cloudinit/config/schemas/schema-cloud-config-v1.json
index 42dc7ebc..9b314077 100644
--- a/cloudinit/config/schemas/schema-cloud-config-v1.json
+++ b/cloudinit/config/schemas/schema-cloud-config-v1.json
@@ -1,6 +1,111 @@
 {
   "$schema": "http://json-schema.org/draft-04/schema#",
   "$defs": {
+    "all_modules": {
+      "enum": [
+        "ansible",
+        "apk-configure",
+        "apk_configure",
+        "apt-configure",
+        "apt_configure",
+        "apt-pipelining",
+        "apt_pipelining",
+        "bootcmd",
+        "byobu",
+        "ca-certs",
+        "ca_certs",
+        "chef",
+        "disable-ec2-metadata",
+        "disable_ec2_metadata",
+        "disk-setup",
+        "disk_setup",
+        "fan",
+        "final-message",
+        "final_message",
+        "growpart",
+        "grub-dpkg",
+        "grub_dpkg",
+        "install-hotplug",
+        "install_hotplug",
+        "keyboard",
+        "keys-to-console",
+        "keys_to_console",
+        "landscape",
+        "locale",
+        "lxd",
+        "mcollective",
+        "migrator",
+        "mounts",
+        "ntp",
+        "package-update-upgrade-install",
+        "package_update_upgrade_install",
+        "phone-home",
+        "phone_home",
+        "power-state-change",
+        "power_state_change",
+        "puppet",
+        "refresh-rmc-and-interface",
+        "refresh_rmc_and_interface",
+        "reset-rmc",
+        "reset_rmc",
+        "resizefs",
+        "resolv-conf",
+        "resolv_conf",
+        "rh-subscription",
+        "rh_subscription",
+        "rightscale-userdata",
+        "rightscale_userdata",
+        "rsyslog",
+        "runcmd",
+        "salt-minion",
+        "salt_minion",
+        "scripts-per-boot",
+        "scripts_per_boot",
+        "scripts-per-instance",
+        "scripts_per_instance",
+        "scripts-per-once",
+        "scripts_per_once",
+        "scripts-user",
+        "scripts_user",
+        "scripts-vendor",
+        "scripts_vendor",
+        "seed-random",
+        "seed_random",
+        "set-hostname",
+        "set_hostname",
+        "set-passwords",
+        "set_passwords",
+        "snap",
+        "spacewalk",
+        "ssh",
+        "ssh-authkey-fingerprints",
+        "ssh_authkey_fingerprints",
+        "ssh-import-id",
+        "ssh_import_id",
+        "timezone",
+        "ubuntu-advantage",
+        "ubuntu_advantage",
+        "ubuntu-autoinstall",
+        "ubuntu_autoinstall",
+        "ubuntu-drivers",
+        "ubuntu_drivers",
+        "update-etc-hosts",
+        "update_etc_hosts",
+        "update-hostname",
+        "update_hostname",
+        "users-groups",
+        "users_groups",
+        "wireguard",
+        "write-files",
+        "write_files",
+        "write-files-deferred",
+        "write_files_deferred",
+        "yum-add-repo",
+        "yum_add_repo",
+        "zypper-add-repo",
+        "zypper_add_repo"
+      ]
+    },
     "users_groups.groups_by_groupname": {
       "additionalProperties": false,
       "patternProperties": {
@@ -231,6 +336,31 @@
       },
       "minProperties": 1
     },
+    "modules_definition": {
+      "type": "array",
+      "items": {
+        "oneOf": [
+          {
+            "$ref": "#/$defs/all_modules"
+          },
+          {
+            "type": "array",
+            "prefixItems": [
+              { "enum": {"$ref": "#/$defs/all_modules"}},
+              { "enum": ["always", "once", "once-per-instance"]}
+            ]
+          }
+        ]
+      }
+    },
+    "base_config": {
+      "type": "object",
+      "properties": {
+        "cloud_init_modules": {"$ref": "#/$defs/modules_definition"},
+        "cloud_config_modules": {"$ref": "#/$defs/modules_definition"},
+        "cloud_final_modules": {"$ref": "#/$defs/modules_definition"}
+      }
+    },
     "cc_ubuntu_autoinstall": {
       "type": "object",
       "properties": {
@@ -2684,6 +2814,7 @@
     }
   },
   "allOf": [
+    { "$ref": "#/$defs/base_config"},
     { "$ref": "#/$defs/cc_ansible" },
     { "$ref": "#/$defs/cc_apk_configure" },
     { "$ref": "#/$defs/cc_apt_configure" },
diff --git a/config/cloud.cfg.tmpl b/config/cloud.cfg.tmpl
index fa250a51..daf31d12 100644
--- a/config/cloud.cfg.tmpl
+++ b/config/cloud.cfg.tmpl
@@ -1,6 +1,7 @@
 ## template:jinja
+
 # The top level settings are used as module
-# and system configuration.
+# and base configuration.
 {% set is_bsd = variant in ["dragonfly", "freebsd", "netbsd", "openbsd"] %}
 {% set is_rhel = variant in ["rhel", "centos"] %}
 {% if is_bsd %}
diff --git a/doc/examples/cloud-config.txt b/doc/examples/cloud-config.txt
index 7f4ded8c..15d788f3 100644
--- a/doc/examples/cloud-config.txt
+++ b/doc/examples/cloud-config.txt
@@ -143,17 +143,6 @@ bootcmd:
  - echo 192.168.1.130 us.archive.ubuntu.com > /etc/hosts
  - [ cloud-init-per, once, mymkfs, mkfs, /dev/vdb ]
 
-# cloud_config_modules:
-# default:
-# cloud_config_modules:
-# - mounts
-# - ssh
-# - apt-update-upgrade
-# - puppet
-# - updates-check
-# - disable-ec2-metadata
-# - runcmd
-#
 # This is an array of arrays or strings.
 # if item is a string, then it is read as a module name
 # if the item is an array it is of the form:
@@ -171,7 +160,6 @@ cloud_config_modules:
  - grub-dpkg
  - [ apt-update-upgrade, always ]
  - puppet
- - updates-check
  - disable-ec2-metadata
  - runcmd
  - byobu
diff --git a/doc/rtd/index.rst b/doc/rtd/index.rst
index 682c7c83..159113f4 100644
--- a/doc/rtd/index.rst
+++ b/doc/rtd/index.rst
@@ -63,7 +63,6 @@ Having trouble? We would like to help!
    topics/format.rst
    topics/examples.rst
    topics/events.rst
-   topics/modules.rst
    topics/merging.rst
 
 .. toctree::
@@ -79,6 +78,14 @@ Having trouble? We would like to help!
 .. toctree::
    :hidden:
    :titlesonly:
+   :caption: Reference
+
+   topics/base_config_reference.rst
+   topics/modules.rst
+
+.. toctree::
+   :hidden:
+   :titlesonly:
    :caption: Development
 
    topics/contributing.rst
diff --git a/doc/rtd/topics/base_config_reference.rst b/doc/rtd/topics/base_config_reference.rst
new file mode 100644
index 00000000..97abcff5
--- /dev/null
+++ b/doc/rtd/topics/base_config_reference.rst
@@ -0,0 +1,363 @@
+.. _base_config_reference:
+
+Base Configuration
+******************
+
+.. warning::
+    This documentation is intended for custom image creators, such as
+    distros and cloud providers, not
+    end users. Modifying the base configuration should not be necessary for
+    end users and can result in a system that may be unreachable or
+    may no longer boot.
+
+Cloud-init base config is primarily defined in two places:
+
+* **/etc/cloud/cloud.cfg**
+* **/etc/cloud/cloud.cfg.d/*.cfg**
+
+See the :ref:`configuration sources explanation<configuration>` for more
+information on how these files get sourced and combined with other
+configuration.
+
+Generation
+==========
+
+``cloud.cfg`` isn't present in any of cloud-init's source files. The
+`configuration is templated`_ and customized for each
+distribution supported by cloud-init.
+
+Base Configuration Keys
+=======================
+
+Module Keys
+-----------
+
+Modules are grouped into the following keys:
+
+* **cloud_init_modules**: Modules run during
+  :ref:`network<topics/boot:network>` timeframe.
+* **cloud_config_modules**: Modules run during
+  :ref:`config<topics/boot:config>` timeframe.
+* **cloud_final_modules**: Modules run during
+  :ref:`final<topics/boot:final>` timeframe.
+
+Each ``modules`` definition contains an array of strings, where each string
+is the name of the module. Each name is taken directly from the
+module filename,
+with the ``cc_`` prefix and ``.py`` suffix removed, and with
+``-`` and ``_`` being interchangeable.
+
+Alternatively, in place of the module name, an array of
+`<name>, <frequency>[, <args>]` args may be specified. See
+:ref:`the module creation guidelines<topics/module_creation:guidelines>` for
+more information on ``frequency`` and ``args``.
+
+.. note::
+    Most modules won't run at all if they're not triggered via a
+    respective user data key, so removing modules or changing the run
+    frequency is **not** a recommended way to reduce instance boot time.
+
+Examples
+^^^^^^^^
+
+To specify that only `cc_final_message.py`_ run during final
+timeframe:
+
+.. code-block:: yaml
+
+    cloud_final_modules:
+    - final_message
+
+To change the frequency from the default of ``ALWAYS`` to ``ONCE``:
+
+.. code-block:: yaml
+
+    cloud_final_modules:
+    - [final_message, once]
+
+To include default arguments to the module (that may be overridden by
+user data):
+
+.. code-block:: yaml
+
+    cloud_final_modules:
+    - [final_message, once, "my final message"]
+
+.. _datasource_base_config:
+
+Datasource Keys
+---------------
+
+Many datasources allow configuration of the datasource for use in
+querying the datasource for metadata using the ``datasource`` key.
+This configuration is datasource dependent and can be found under
+each datasource's respective :ref:`documentation<datasources>`. It will
+generally take the form of:
+
+.. code-block:: yaml
+
+    datasource:
+      <datasource_name>:
+        ...
+
+System Info Keys
+----------------
+These keys are used for setup of cloud-init itself, or the datasource
+or distro. Anything under the ``system_info`` cannot be overridden by
+vendor data, user data, or any other handlers or transforms. In some cases,
+there may be a ``system_info`` key used for the distro, while the same
+key is used outside of ``system_info`` for a userdata module.
+Both keys will be processed independently.
+
+* **system_info**: Top-level key
+
+  - **paths**: Definitions of common paths used by cloud-init
+
+    + **cloud_dir**: Defaults to ``/var/lib/cloud``
+    + **templates_dir**: Defaults to ``/etc/cloud/templates``
+
+  - **distro**: Name of distro being used.
+  - **default_user**: Defines the default user for the system using the same
+    user configuration as :ref:`topics/modules:users and groups`. Note that
+    this CAN be overridden if a ``users`` configuration
+    is specified without a ``- default`` entry.
+  - **ntp_client**: The default ntp client for the distro. Takes the same
+    form as ``ntp_client`` defined in :ref:`topics/modules:ntp`.
+  - **package_mirrors**: Defines the package mirror info for apt.
+  - **ssh_svcname**: The ssh service name. For most distros this will be
+    either ``ssh`` or ``sshd``.
+  - **network**: Top-level key for distro-specific networking configuration
+
+    + **renderers**: Prioritized list of networking configurations to try
+      on this system. The first valid entry found will be used.
+      Options are:
+
+      * **eni** - For /etc/network/interfaces
+      * **network-manager**
+      * **netplan**
+      * **networkd** - For systemd-networkd
+      * **freebsd**
+      * **netbsd**
+      * **openbsd**
+
+    + **activators**: Prioritized list of networking tools to try to activate
+      network on this system. The first valid entry found will be used.
+      Options are:
+
+      * **eni** - For ``ifup``/``ifdown``
+      * **netplan** - For ``netplan generate``/``netplan apply``
+      * **network-manager** - For ``nmcli connection load``/
+        ``nmcli connection up``
+      * **networkd** - For ``ip link set up``/``ip link set down``
+
+Logging Keys
+------------
+
+See :ref:`the logging explanation<logging>` for a comprehensive
+logging explanation. Note that cloud-init has a default logging
+definition that shouldn't need to be altered. It is defined on the
+instance at ``/etc/cloud/cloud.cfg.d/05_logging.cfg``.
+
+The logging keys used in the base configuration are as follows:
+
+**logcfg**: A standard python `fileConfig`_ formatted log configuration.
+This is the primary logging configuration key and will take precedence over
+**log_cfgs** or **log_basic** keys.
+
+**log_cfgs**: A list of logging configs in `fileConfig`_ format to apply
+when running cloud-init. Note that **log_cfgs** is used in
+``/etc/cloud.cfg.d/05_logging.cfg``.
+
+**log_basic**: Boolean value to determine if cloud-init should apply a
+basic default logging configuration if none has been provided. Defaults
+to ``true`` but only takes effect if **logcfg** or **log_cfgs** hasn't
+been defined.
+
+**output**: If and how to redirect stdout/stderr. Defined in
+``/etc/cloud.cfg.d/05_logging.cfg`` and explained in
+:ref:`the logging explanation<logging_command_output>`.
+
+**syslog_fix_perms**: Takes a list of ``<owner:group>`` strings and will set
+the owner of **def_log_file** accordingly.
+
+**def_log_file**: Only used in conjunction with **syslog_fix_perms**.
+Specifies the filename to be used for setting permissions. Defaults
+to ``/var/log/cloud-init.log``.
+
+Other Keys
+----------
+
+**network**: The :ref:`network_config` to be applied to this instance.
+
+**datasource_pkg_list**: Prioritized list of python packages to search when
+finding a datasource. Automatically includes ``cloudinit.sources``.
+
+**datasource_list**: Prioritized list of datasources that cloud-init will
+attempt to find on boot. By default, this will be defined in
+``/etc/cloud/cloud.cfg.d``. There are two primary use cases for modifying
+the datasource_list:
+
+1. Remove known invalid datasources. This may avoid long timeouts attempting
+   to detect datasources on any system without a systemd-generator hook
+   that invokes ds-identify.
+2. Override default datasource ordering to discover a different datasource
+   type than would typically be prioritized.
+
+If **datasource_list** has only a single entry (or a single entry + ``None``),
+:ref:`cloud-init's generator script<topics/boot:generator>`
+will automatically assume and use this datasource without
+attempting detection.
+
+**vendor_data**/**vendor_data2**: Allows the user to disable ``vendor_data``
+or ``vendor_data2`` along with providing a prefix for any executed scripts.
+
+Format is a dict with ``enabled`` and ``prefix`` keys:
+
+* **enabled**: Boolean indicating whether to enable or disable the vendor_data
+* **prefix**: A path to prepend to any vendor_data provided script
+
+Example
+=======
+
+On an ubuntu system, ``/etc/cloud/cloud.cfg`` should look similar to:
+
+.. code-block:: yaml
+
+    # The top level settings are used as module and base configuration.
+    # A set of users which may be applied and/or used by various modules
+    # when a 'default' entry is found it will reference the 'default_user'
+    # from the distro configuration specified below
+    users:
+    - default
+
+
+    # If this is set, 'root' will not be able to ssh in and they
+    # will get a message to login instead as the default $user
+    disable_root: true
+
+    # This will cause the set+update hostname module to not operate (if true)
+    preserve_hostname: false
+
+    # If you use datasource_list array, keep array items in a single line.
+    # If you use multi line array, ds-identify script won't read array items.
+    # Example datasource config
+    # datasource:
+    #    Ec2:
+    #      metadata_urls: [ 'blah.com' ]
+    #      timeout: 5 # (defaults to 50 seconds)
+    #      max_wait: 10 # (defaults to 120 seconds)
+
+    # The modules that run in the 'init' stage
+    cloud_init_modules:
+    - migrator
+    - seed_random
+    - bootcmd
+    - write-files
+    - growpart
+    - resizefs
+    - disk_setup
+    - mounts
+    - set_hostname
+    - update_hostname
+    - update_etc_hosts
+    - ca-certs
+    - rsyslog
+    - users-groups
+    - ssh
+
+    # The modules that run in the 'config' stage
+    cloud_config_modules:
+    - snap
+    - ssh-import-id
+    - keyboard
+    - locale
+    - set-passwords
+    - grub-dpkg
+    - apt-pipelining
+    - apt-configure
+    - ubuntu-advantage
+    - ntp
+    - timezone
+    - disable-ec2-metadata
+    - runcmd
+    - byobu
+
+    # The modules that run in the 'final' stage
+    cloud_final_modules:
+    - package-update-upgrade-install
+    - fan
+    - landscape
+    - lxd
+    - ubuntu-drivers
+    - write-files-deferred
+    - puppet
+    - chef
+    - mcollective
+    - salt-minion
+    - reset_rmc
+    - refresh_rmc_and_interface
+    - rightscale_userdata
+    - scripts-vendor
+    - scripts-per-once
+    - scripts-per-boot
+    - scripts-per-instance
+    - scripts-user
+    - ssh-authkey-fingerprints
+    - keys-to-console
+    - install-hotplug
+    - phone-home
+    - final-message
+    - power-state-change
+
+    # System and/or distro specific settings
+    # (not accessible to handlers/transforms)
+    system_info:
+      # This will affect which distro class gets used
+      distro: ubuntu
+      # Default user name + that default users groups (if added/used)
+      default_user:
+        name: ubuntu
+        lock_passwd: True
+        gecos: Ubuntu
+        groups: [adm, audio, cdrom, dialout, dip, floppy, lxd, netdev, plugdev, sudo, video]
+        sudo: ["ALL=(ALL) NOPASSWD:ALL"]
+        shell: /bin/bash
+      network:
+        renderers: ['netplan', 'eni', 'sysconfig']
+      # Automatically discover the best ntp_client
+      ntp_client: auto
+      # Other config here will be given to the distro class and/or path classes
+      paths:
+        cloud_dir: /var/lib/cloud/
+        templates_dir: /etc/cloud/templates/
+      package_mirrors:
+        - arches: [i386, amd64]
+        failsafe:
+            primary: http://archive.ubuntu.com/ubuntu
+            security: http://security.ubuntu.com/ubuntu
+        search:
+            primary:
+            - http://%(ec2_region)s.ec2.archive.ubuntu.com/ubuntu/
+            - http://%(availability_zone)s.clouds.archive.ubuntu.com/ubuntu/
+            - http://%(region)s.clouds.archive.ubuntu.com/ubuntu/
+            security: []
+        - arches: [arm64, armel, armhf]
+        failsafe:
+            primary: http://ports.ubuntu.com/ubuntu-ports
+            security: http://ports.ubuntu.com/ubuntu-ports
+        search:
+            primary:
+            - http://%(ec2_region)s.ec2.ports.ubuntu.com/ubuntu-ports/
+            - http://%(availability_zone)s.clouds.ports.ubuntu.com/ubuntu-ports/
+            - http://%(region)s.clouds.ports.ubuntu.com/ubuntu-ports/
+            security: []
+        - arches: [default]
+        failsafe:
+            primary: http://ports.ubuntu.com/ubuntu-ports
+            security: http://ports.ubuntu.com/ubuntu-ports
+      ssh_svcname: ssh
+
+
+.. _configuration is templated: https://github.com/canonical/cloud-init/blob/main/config/cloud.cfg.tmpl
+.. _cc_final_message.py: https://github.com/canonical/cloud-init/blob/main/cloudinit/config/cc_final_message.py
+.. _fileConfig: https://docs.python.org/3/library/logging.config.html#logging-config-fileformat
diff --git a/doc/rtd/topics/datasources/exoscale.rst b/doc/rtd/topics/datasources/exoscale.rst
index 9074edc6..2d2e4544 100644
--- a/doc/rtd/topics/datasources/exoscale.rst
+++ b/doc/rtd/topics/datasources/exoscale.rst
@@ -38,8 +38,9 @@ Configuration
 Users of this datasource are discouraged from changing the default settings
 unless instructed to by Exoscale support.
 
-The following settings are available and can be set for the datasource in
-system configuration (in `/etc/cloud/cloud.cfg.d/`).
+The following settings are available and can be set for the
+:ref:`datasource base configuration<datasource_base_config>`
+(in `/etc/cloud/cloud.cfg.d/`).
 
 The settings available are:
 
diff --git a/doc/rtd/topics/datasources/smartos.rst b/doc/rtd/topics/datasources/smartos.rst
index 55604ffb..6fe45c73 100644
--- a/doc/rtd/topics/datasources/smartos.rst
+++ b/doc/rtd/topics/datasources/smartos.rst
@@ -125,7 +125,9 @@ are provided by SmartOS:
  * user-data
  * user-script
 
-This list can be changed through system config of variable 'no_base64_decode'.
+This list can be changed through
+:ref:`datasource base configuration<datasource_base_config>` variable
+'no_base64_decode'.
 
 This means that user-script and user-data as well as other values can be
 base64 encoded. Since Cloud-init can only guess as to whether or not something
diff --git a/doc/rtd/topics/faq.rst b/doc/rtd/topics/faq.rst
index 49399986..8dae49e9 100644
--- a/doc/rtd/topics/faq.rst
+++ b/doc/rtd/topics/faq.rst
@@ -47,6 +47,9 @@ Cloud-init config is provided in two places:
 These files can define the modules that run during instance initialization,
 the datasources to evaluate on boot, and other settings.
 
+See the :ref:`configuration sources explanation<configuration>` and
+:ref:`configuration reference<base_config_reference>` for more information.
+
 Where are the data files?
 =========================
 
diff --git a/doc/rtd/topics/instancedata.rst b/doc/rtd/topics/instancedata.rst
index a5b297e1..575dbf1b 100644
--- a/doc/rtd/topics/instancedata.rst
+++ b/doc/rtd/topics/instancedata.rst
@@ -181,10 +181,10 @@ Top-level keys:
   'security sensitive'. Only the keys listed here will be redacted from
   instance-data.json for non-root users.
 
-* **merged_cfg**: Merged cloud-init 'system_config' from `/etc/cloud/cloud.cfg`
-  and  `/etc/cloud/cloud-cfg.d`. Values under this key could contain sensitive
-  information such as passwords, so it is included in the **sensitive-keys**
-  list which is only readable by root.
+* **merged_cfg**: Merged cloud-init :ref:`base_config_reference` from
+  `/etc/cloud/cloud.cfg` and  `/etc/cloud/cloud-cfg.d`. Values under this key
+  could contain sensitive information such as passwords, so it is included in
+  the **sensitive-keys** list which is only readable by root.
 
 * **ds**: Datasource-specific metadata crawled for the specific cloud
   platform. It should closely represent the structure of the cloud metadata
@@ -375,7 +375,7 @@ EC2 instance:
    "availability_zone": "us-east-1b",
    "base64_encoded_keys": [],
    "merged_cfg": {
-    "_doc": "Merged cloud-init system config from /etc/cloud/cloud.cfg and /etc/cloud/cloud.cfg.d/",
+    "_doc": "Merged cloud-init base config from /etc/cloud/cloud.cfg and /etc/cloud/cloud.cfg.d/",
     "_log": [
      "[loggers]\nkeys=root,cloudinit\n\n[handlers]\nkeys=consoleHandler,cloudLogHandler\n\n[formatters]\nkeys=simpleFormatter,arg0Formatter\n\n[logger_root]\nlevel=DEBUG\nhandlers=consoleHandler,cloudLogHandler\n\n[logger_cloudinit]\nlevel=DEBUG\nqualname=cloudinit\nhandlers=\npropagate=1\n\n[handler_consoleHandler]\nclass=StreamHandler\nlevel=WARNING\nformatter=arg0Formatter\nargs=(sys.stderr,)\n\n[formatter_arg0Formatter]\nformat=%(asctime)s - %(filename)s[%(levelname)s]: %(message)s\n\n[formatter_simpleFormatter]\nformat=[CLOUDINIT] %(filename)s[%(levelname)s]: %(message)s\n",
      "[handler_cloudLogHandler]\nclass=FileHandler\nlevel=DEBUG\nformatter=arg0Formatter\nargs=('/var/log/cloud-init.log',)\n",
diff --git a/doc/rtd/topics/logging.rst b/doc/rtd/topics/logging.rst
index f72b77c1..4d0a14ca 100644
--- a/doc/rtd/topics/logging.rst
+++ b/doc/rtd/topics/logging.rst
@@ -1,3 +1,5 @@
+.. _logging:
+
 *******
 Logging
 *******
@@ -98,8 +100,10 @@ the default format string ``%(message)s``::
 For additional information about configuring python's logging module, please
 see the documentation for `python logging config`_.
 
+.. _logging_command_output:
+
 Command Output
---------------
+==============
 Cloud-init can redirect its stdout and stderr based on config given under the
 ``output`` config key. The output of any commands run by cloud-init and any
 user or vendor scripts provided will also be included here. The ``output`` key
diff --git a/doc/rtd/topics/module_creation.rst b/doc/rtd/topics/module_creation.rst
index c0bf4003..56cadec4 100644
--- a/doc/rtd/topics/module_creation.rst
+++ b/doc/rtd/topics/module_creation.rst
@@ -66,7 +66,9 @@ Guidelines
     instance types.
   * ``log``: A logger object that can be used to log messages.
   * ``args``: An argument list. This is usually empty and is only populated
-    if the module is called independently from the command line.
+    if the module is called independently from the command line or if the
+    module definition in ``/etc/cloud/cloud.cfg[.d]`` has been modified
+    to pass arguments to this module.
 
 * If your module introduces any new cloud-config keys, you must provide a
   schema definition in `cloud-init-schema.json`_.
diff --git a/doc/rtd/topics/network-config-format-v1.rst b/doc/rtd/topics/network-config-format-v1.rst
index 68a9cefa..a9dd31af 100644
--- a/doc/rtd/topics/network-config-format-v1.rst
+++ b/doc/rtd/topics/network-config-format-v1.rst
@@ -10,7 +10,8 @@ creation (bonds, bridges, vlans) routes and DNS configuration.
 Required elements of a Network Config Version 1 are ``config`` and
 ``version``.
 
-Cloud-init will read this format from system config.
+Cloud-init will read this format from :ref:`base_config_reference`.
+
 For example the following could be present in
 ``/etc/cloud/cloud.cfg.d/custom-networking.cfg``:
 
diff --git a/doc/rtd/topics/network-config-format-v2.rst b/doc/rtd/topics/network-config-format-v2.rst
index 952d15ae..53274417 100644
--- a/doc/rtd/topics/network-config-format-v2.rst
+++ b/doc/rtd/topics/network-config-format-v2.rst
@@ -30,7 +30,8 @@ The ``network`` key has at least two required elements.  First
 it must include ``version: 2``  and one or more of possible device
 ``types``.
 
-Cloud-init will read this format from system config.
+Cloud-init will read this format from :ref:`base_config_reference`.
+
 For example the following could be present in
 ``/etc/cloud/cloud.cfg.d/custom-networking.cfg``::
 
diff --git a/doc/rtd/topics/network-config.rst b/doc/rtd/topics/network-config.rst
index 3e48555f..b6d7a9be 100644
--- a/doc/rtd/topics/network-config.rst
+++ b/doc/rtd/topics/network-config.rst
@@ -1,3 +1,5 @@
+.. _network_config:
+
 *********************
 Network Configuration
 *********************
diff --git a/tests/unittests/config/test_schema.py b/tests/unittests/config/test_schema.py
index a401ffd4..50128f2c 100644
--- a/tests/unittests/config/test_schema.py
+++ b/tests/unittests/config/test_schema.py
@@ -165,6 +165,7 @@ class TestGetSchema:
         assert ["$defs", "$schema", "allOf"] == sorted(list(schema.keys()))
         # New style schema should be defined in static schema file in $defs
         expected_subschema_defs = [
+            {"$ref": "#/$defs/base_config"},
             {"$ref": "#/$defs/cc_ansible"},
             {"$ref": "#/$defs/cc_apk_configure"},
             {"$ref": "#/$defs/cc_apt_configure"},