automate: Add netmiko and napalm examples

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+:lastproofread: 2021-07-12
+
+.. _cloud-init:
+
+###############
+VyOS cloud-init
+###############
+
+Cloud and virtualized instances of VyOS are initialized using the
+industry-standard cloud-init. Via cloud-init, the system performs tasks such as
+injecting SSH keys and configuring the network. In addition, the user can supply
+a custom configuration at the time of instance launch.
+
+**************
+Config Sources
+**************
+
+VyOS support three types of config sources.
+
+* Metadata - Metadata is sourced by the cloud platform or hypervisor.
+  In some clouds, there is implemented as an HTTP endpoint at
+  http://169.254.169.254.
+* Network configuration - This config source informs the system about the
+  network settings like IP addresses, routes, DNS. Available only in several
+  cloud and virtualization platforms.
+* User-data - User-data is specified by the user. This config source offers the
+  ability to insert any CLI configuration commands into the configuration before
+  the first boot.
+
+*********
+User-data
+*********
+
+Major cloud providers offer a means of providing user-data at the time of
+instance launch. It can be provided as plain text or as base64-encoded text,
+depending on cloud provider. Also, it can be compressed using gzip, which makes
+sense with a long configuration commands list, because of the hard limit to
+~16384 bytes for the whole user-data.
+
+The easiest way to configure the system via user-data is the Cloud-config syntax
+described below.
+
+********************
+Cloud-config modules
+********************
+
+In VyOS, by default, enabled only two modules:
+
+* ``write_files`` - this module allows to insert any files into the filesystem
+  before the first boot, for example, pre-generated encryption keys,
+  certificates, or even a whole ``config.boot`` file.
+* ``vyos_userdata`` - the module accepts a list of CLI configuration commands in
+  a ``vyos_config_commands`` section, which gives an easy way to configure the
+  system during deployment.
+
+************************
+cloud-config file format
+************************
+
+A cloud-config document is written in YAML. The file must begin
+with ``#cloud-config`` line. The key used to designate a VyOS configuration
+is ``vyos_config_commands``. What follows is VyOS configuration using
+the "set-style" syntax. Both "set" and "delete" commands are supported.
+
+Commands requirements:
+
+* one command per line
+* if command ends in a value, it must be inside single quotes
+* a single-quote symbol is not allowed inside command or value
+
+The commands list produced by the ``show configuration commands`` command on a
+VyOS router should comply with all the requirements, so it is easy to get a 
+proper commands list by copying it from another router.
+
+The configuration specified in the cloud-config document overwrites default
+configuration values and values configured via Metadata.
+
+Here is an example cloud-config.
+
+.. code-block:: yaml
+
+   #cloud-config
+   vyos_config_commands:
+     - set system host-name 'vyos-prod-ashburn'
+     - set system ntp server 1.pool.ntp.org
+     - set system ntp server 2.pool.ntp.org
+     - delete interfaces ethernet eth1 address 'dhcp'
+     - set interfaces ethernet eth1 address '192.0.2.247/24'
+     - set protocols static route 198.51.100.0/24 next-hop '192.0.2.1'
+
+*************************
+System Defaults/Fallbacks
+*************************
+
+These are the VyOS defaults and fallbacks.
+
+* SSH is configured on port 22
+* ``vyos``/``vyos`` credentials if no others specified by data source
+* DHCP on first Ethernet interface if no network configuration is provided
+
+All of these can be overridden using the configuration in user-data.
+
+***************
+Troubleshooting
+***************
+
+If you encounter problems, verify that the cloud-config document contains
+valid YAML. Online resources such as https://yamlvalidator.com/ provide
+a simple tool for validating YAML.
+
+cloud-init logs to /var/log/cloud-init.log. This file can be helpful in
+determining why the configuration varies from what you expect. You can fetch the
+most important data filtering output for ``vyos`` keyword:
+
+.. code-block:: none
+
+    sudo grep vyos /var/log/cloud-init.log
+