[scanner] initial documentation

Note: still needs to patch main cdist(1) manpage

docs/src/cdist-scan.rst

@@ -0,0 +1,99 @@
+Scan
+=====
+
+Description
+-----------
+Runs cdist as a daemon that discover/watch on hosts and reconfigure them
+periodically. It is especially useful in netboot-based environment where hosts
+boot unconfigured, and to ensure your infrastructure stays in sync with your
+configuration.
+
+This feature is still consider to be in **beta** stage.
+
+Usage (Examples)
+----------------
+
+Discover hosts on local network and configure those whose name is resolved by
+the name mapper script.
+
+.. code-block:: sh
+
+    $ cdist scan --beta --interface eth0 \
+      --mode scan --name-mapper path/to/script \
+      --mode trigger --mode config
+
+List known hosts and exit.
+
+.. code-block:: sh
+
+    $ cdist scan --beta --list --name-mapper path/to/script
+
+Please refer to `cdist(1)` for a detailed list of parameters.
+
+Modes
+-----
+
+The scanner has 3 modes that can be independently toggled. If the `--mode`
+parameter is not specified, only `tigger` and `scan` are enabled (= hosts are
+not configured).
+
+trigger
+  Send ICMPv6 requests to specific hosts or broadcast over IPv6 link-local to
+  trigger detection by the `scan` module.
+
+scan
+  Watch for incoming ICMPv6 replies and optionally configure detected hosts.
+
+config
+  Enable configuration of hosts detected by `scan`.
+
+Name Mapper Script
+------------------
+
+The name mapper script takes an IPv6 address as first argument and writes the
+resolved name to stdout - if any. The script must be executable.
+
+Simplest script:
+
+.. code-block:: sh
+  #!/bin/sh
+
+  case "$1" in
+  	"fe80::20d:b9ff:fe57:3524")
+  		printf "my-host-01"
+  		;;
+  	"fe80::7603:bdff:fe05:89bb")
+  		printf "my-host-02"
+  		;;
+  esac
+
+Resolving name from `PTR` DNS record:
+
+.. code-block:: sh
+  #!/bin/sh
+
+  for cmd in dig sed; do
+  	if ! command -v $cmd > /dev/null; then
+  		exit 1
+  	fi
+  done
+
+  dig +short -x "$1" | sed -e 's/.$//'
+
+
+Trigger Source Script
+---------------------
+
+This script returns a list of addresses (separated by a newline) to be used by
+`trigger` mode. It is not used to map names. The script must be executable.
+
+Simplest script:
+
+.. code-block:: sh
+  #!/bin/sh
+
+  cat << EOF
+  server1.domain.tld
+  server2.domain.tld
+  server3.domain.tld
+  EOF

docs/src/index.rst

@@ -34,6 +34,7 @@ It natively supports IPv6 since the first release.
    cdist-parallelization
    cdist-inventory
    cdist-preos
+   cdist-scan
    cdist-integration
    cdist-reference
    cdist-best-practice