[PATCH proxmox-backup v7 27/41] docs: notifications: rework matcher sections, describe expression option

[Lukas Wagner <l.wagner@proxmox.com>]

In the matcher section, focus on the higher-level concepts first, as
this resembles what the user actually has to understand to use the UI.
Move configuration options that are used in the configuration file and
API to a separate subsection. Furthermore, add a brief section
demonstrating the JSON format used by match expressions.

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
---

Notes:
    New in v6.

 docs/notifications.rst | 227 +++++++++++++++++++++++++++++++++--------
 1 file changed, 184 insertions(+), 43 deletions(-)

diff --git a/docs/notifications.rst b/docs/notifications.rst
index 440c700a4..3e2b66ce5 100644
--- a/docs/notifications.rst
+++ b/docs/notifications.rst
@@ -195,63 +195,204 @@ Notification Matchers
 
 Notification matchers route notifications to notification targets based on
 their matching rules. These rules can match certain properties of a
-notification, such as the timestamp (``match-calendar``), the severity of the
-notification (``match-severity``) or metadata fields (``match-field``). If a
-notification is matched by a matcher, all targets configured for the matcher
-will receive the notification.
+notification, such as the timestamp, the severity of the notification or
+metadata fields, as well as arbitrary combinations of these. If a notification
+is matched by a matcher, all targets configured for the matcher will receive
+the notification.
 
-An arbitrary number of matchers can be created, each with with their own
-matching rules and targets to notify. Every target is notified at most once for
-every notification, even if the target is used in multiple matchers.
+An arbitrary number of matchers can be created, each with their own match rules
+and targets to notify. Every target is notified at most once for every
+notification, even if the target is used in multiple matchers.
 
-A matcher without rules matches any notification; the configured targets will
-always be notified.
+Match Rules
+^^^^^^^^^^^
+
+Notification matchers can be configured in the GUI under *Configuration →
+Notifications*. Matchers can be created, modified and deleted from this view.
+
+When editing a matcher, match rules can be edited under the *Match Rules* tab.
+Rules are represented as a tree. Each tree node can either match on properties
+of a notification (fields, severity or timestamp) or combine the results of
+child nodes (e.g. *All sub-rules match*). Combinator nodes can be nested, which
+makes it possible to compose arbitrarily complex matching behavior.
+
+The following node types are available:
+
+* **Always match**: Match any notification.
+
+* **All sub-rules match**: All direct children of this node must match.
+
+* **At least one sub-rule matches**: At least one direct child of this node
+  must match.
+
+* **Exactly one sub-rule matches**: Exactly one direct child of this node must
+  match.
+
+* **Match Field**: Match a metadata field of a notification. This node can
+  either match if the field value matches one of the values provided, or,
+  alternatively, if it matches a regular expression. Available fields are
+  listed in :ref:`notification_events`.
+
+* **Match Calendar**: Check if the timestamp of a notification is within a
+  configured time range, based on a selection of weekdays and one contiguous
+  time range within each day (e.g. Monday to Friday, 09:00 to 17:00). If
+  multiple time ranges within a day must be matched, use an **At least one
+  sub-rule matches** node with one **Match Calendar** child per time range.
+
+* **Match Severity**: Match the severity of a notification. The following
+  severity levels are available: ``info``, ``notice``, ``warning``, ``error``
+  and ``unknown``. Each **Match Severity** node can specify multiple severity
+  levels it matches on, for instance ``info`` and ``notice``.
+
+Each node in the tree can be inverted by checking **Invert Rule**. For instance,
+for a **Match Severity** node matching on ``info``, checking **Invert Rule**
+lets the node match on ``notice``, ``warning``, ``error`` and ``unknown``.
+
+Under the *Targets to Notify* tab, one or more notification targets can be
+selected. All selected targets are notified if a notification is matched.
+
+Matcher Configuration Options
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section gives an overview of the options used by matchers in the
+configuration file and in the API.
+
+The following options are used in configuration entries for matchers:
+
+* ``target``: Determine which target should be notified if the matcher
+  matches. Can be used multiple times to notify multiple targets.
+* ``disable``: Don't evaluate this matcher.
+* ``comment``: Comment for this matcher.
+* The matching behavior is defined either by the ``expression`` option or by
+  the deprecated options below; the two cannot be combined.
+
+  * Expression-based matchers (preferred):
+
+    * ``expression``: Ruleset for this matcher as a single JSON-serialized
+      object (:ref:`notification_match_expression_reference`).
+
+  * Deprecated matcher options:
+
+    * ``invert-match``: Inverts the result of the whole matcher.
+    * ``mode``: Determines how the individual match rules are evaluated to
+      compute the result for the whole matcher. If set to ``all``, all
+      matching rules must match. If set to ``any``, at least one rule must
+      match. Defaults to ``all``.
+
+    * ``match-calendar``: Match the notification's timestamp against a
+      schedule. Days can be specified as an inclusive range (e.g.
+      ``mon..wed``) or enumerated (e.g. ``mon,wed,sat``). If no days are
+      specified, the time range applies to every day of the week (e.g.
+      ``08:00-12:00``). Examples:
+
+      * ``match-calendar mon..wed 9-12``
+      * ``match-calendar mon,wed,sat 08:15-12:35``
+      * ``match-calendar 04:15-16:35``
+
+    * ``match-field``: Match a notification's metadata field, either against
+      a list of matched values, or as a regular expression. If the field does
+      not exist, the notification will not be matched. Examples:
+
+      * ``match-field exact:type=gc``
+      * ``match-field exact:type=prune,verify``
+      * ``match-field regex:datastore=^backup-.*$``
+
+    * ``match-severity``: Match the notification's severity. Examples:
+
+      * ``match-severity error``
+      * ``match-severity warning,error,unknown``
+
+A matcher without any matching rules always matches; the configured targets
+will always be notified.
+
+Starting with Proxmox Backup Server 4.3, match rules created and edited via the
+GUI are stored as a single option ``expression`` in the respective matcher
+configuration entry. The previously used options (``match-field``,
+``match-calendar``, ``match-severity``, ``mode`` and ``invert-match``) will
+continue to be supported at least until the next major release.
+
+.. NOTE:: Any existing matcher will be migrated to use the newer ``expression``
+   option when edited through the GUI.
 
 See :ref:`notifications.cfg` for all configuration options.
 
-Calendar Matching Rules
-^^^^^^^^^^^^^^^^^^^^^^^
-A calendar matcher matches a notification's timestamp.
+.. _notification_match_expression_reference:
 
-Examples:
+Match Expression Reference
+^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-* ``match-calendar 8-12``
-* ``match-calendar 8:00-15:30``
-* ``match-calendar mon-fri 9:00-17:00``
-* ``match-calendar sun,tue-wed,fri 9-17``
+This section describes the representation used to encode rules in the
+``expression`` parameter.
 
-Field Matching Rules
-^^^^^^^^^^^^^^^^^^^^
-Notifications have a selection of metadata fields that can be matched. When
-using ``exact`` as a matching mode, a ``,`` can be used as a separator. The
-matching rule then matches if the metadata field has **any** of the specified
-values.
+The ``expression`` option contains a JSON-formatted tree structure of rules,
+with leaf nodes matching on the properties of a notification (``field``,
+``severity``, ``calendar``) or representing constants (``constant``).
+Intermediate nodes and the root node encode the relationship between them
+(``all-of``, ``any-of``, ``one-of``, ``not``).
 
-Examples:
+============ ======================================================== ========= ===============================
+Node Type    Description                                              Leaf Node Example
+============ ======================================================== ========= ===============================
+``all-of``   Match if all child nodes match                           No        ``{"all-of": [<expr>]}``
+``any-of``   Match if any child node matches                          No        ``{"any-of": [<expr>]}``
+``one-of``   Match if exactly one child node matches                  No        ``{"one-of": [<expr>]}``
+``not``      Invert the result of a single child node                 No        ``{"not": <expr>}``
+``constant`` Always or never matches, depending on the boolean value  Yes       ``{"constant": true|false}``
+``match``    Match on a property of a notification                    Yes       ``{"match": <match-expr>}``
+============ ======================================================== ========= ===============================
 
-* ``match-field exact:type=gc`` Only match notifications for garbage collection
-  jobs
-* ``match-field exact:type=prune,verify`` Match prune job and verification job
-  notifications.
-* ``match-field regex:datastore=^backup-.*$`` Match any datastore starting with
-  ``backup``.
+``match`` leaf nodes can have the following variants (``<match-expr>``):
 
-If a notification does not have the matched field, the rule will **not** match.
-For instance, a ``match-field regex:datastore=.*`` directive will match any
-notification that has a ``datastore`` metadata field, but will not match if the
-field does not exist.
+============ =========================================================================== ===================================================================
+Match Type   Description                                                                 Example
+============ =========================================================================== ===================================================================
+``calendar`` Check if the notification's timestamp is within a configured time range     ``{"type": "calendar", "schedule": "mon..fri 9-17"}``
+``field``    Check a notification's fields against a regex or a list of permitted values ``{"type": "field", "field": "job-id", "values": ["a", "b"]}`` or
+                                                                                         ``{"type": "field", "field": "datastore", "regex": "^backup-.*$"}``
+``severity`` Check a notification's severity against a list of permitted values          ``{"type": "severity", "severities": ["info", "notice"]}``
+============ =========================================================================== ===================================================================
 
-Severity Matching Rules
-^^^^^^^^^^^^^^^^^^^^^^^
-A notification has a associated severity that can be matched.
+A pretty-printed, full example of a non-trivial expression is shown below. It
+encodes an expression matching on garbage collection jobs (``gc``), but only
+within a given time range (``mon..fri 09:00-17:00``) or if it has a severity of
+``warning`` or ``error``. In the API and configuration file, the JSON is
+expected to be stored as a single line, as the value of the ``expression``
+option; the line breaks and indentation are only for demonstration purposes.
 
-Examples:
+.. code-block:: json
 
-* ``match-severity error``: Only match errors
-* ``match-severity warning,error``: Match warnings and error
-
-The following severities are in use:
-``info``, ``notice``, ``warning``, ``error``, ``unknown``.
+  {
+    "all-of": [
+      {
+        "any-of": [
+          {
+            "match": {
+              "type": "calendar",
+              "schedule": "mon..fri 09:00-17:00"
+            }
+          },
+          {
+            "match": {
+              "type": "severity",
+              "severities": [
+                "warning",
+                "error"
+              ]
+            }
+          }
+        ]
+      },
+      {
+        "match": {
+          "type": "field",
+          "field": "type",
+          "values": [
+            "gc"
+          ]
+        }
+      }
+    ]
+  }
 
 .. _notification_events:
 
-- 
2.47.3