Diff

Statistics: Rewrite statistics backends to use OpenMetrics The metric subsystem of Prosody has had some shortcomings from the perspective of the current state-of-the-art in metric observability. The OpenMetrics standard [0] is a formalization of the data model (and serialization format) of the well-known and widely-used Prometheus [1] software stack. The previous stats subsystem of Prosody did not map well to that format (see e.g. [2] and [3]); the key reason is that it was trying to do too much math on its own ([2]) while lacking first-class support for "families" of metrics ([3]) and structured metric metadata (despite the `extra` argument to metrics, there was no standard way of representing common things like "tags" or "labels"). Even though OpenMetrics has grown from the Prometheus world of monitoring, it maps well to other popular monitoring stacks such as: - InfluxDB (labels can be mapped to tags and fields as necessary) - Carbon/Graphite (labels can be attached to the metric name with dot-separation) - StatsD (see graphite when assuming that graphite is used as backend, which is the default) The util.statsd module has been ported to use the OpenMetrics model as a proof of concept. An implementation which exposes the util.statistics backend data as Prometheus metrics is ready for publishing in prosody-modules (most likely as mod_openmetrics_prometheus to avoid breaking existing 0.11 deployments). At the same time, the previous measure()-based API had one major advantage: It is really simple and easy to use without requiring lots of knowledge about OpenMetrics or similar concepts. For that reason as well as compatibility with existing code, it is preserved and may even be extended in the future. However, code relying on the `stats-updated` event as well as `get_stats` from `statsmanager` will break because the data model has changed completely; in case of `stats-updated`, the code will simply not run (as the event was renamed in order to avoid conflicts); the `get_stats` function has been removed completely (so it will cause a traceback when it is attempted to be used). Note that the measure_*_event methods have been removed from the module API. I was unable to find any uses or documentation and thus deemed they should not be ported. Re-implementation is possible when necessary. [0]: https://openmetrics.io/ [1]: https://prometheus.io/ [2]: #959 [3]: #960

--- a/core/moduleapi.lua	Sun Apr 25 17:32:27 2021 +0200
+++ b/core/moduleapi.lua	Sun Apr 18 11:47:41 2021 +0200
@@ -510,26 +510,33 @@
 
 function api:measure(name, stat_type, conf)
 	local measure = require "core.statsmanager".measure;
-	return measure(stat_type, "/"..self.host.."/mod_"..self.name.."/"..name, conf);
+	local fixed_label_key, fixed_label_value
+	if self.host ~= "*" then
+		fixed_label_key = "host"
+		fixed_label_value = self.host
+	end
+	-- new_legacy_metric takes care of scoping for us, as it does not accept
+	-- an array of labels
+	-- the prosody_ prefix is automatically added by statsmanager for legacy
+	-- metrics.
+	return measure(stat_type, "mod_"..self.name.."/"..name, conf, fixed_label_key, fixed_label_value)
 end
 
-function api:measure_object_event(events_object, event_name, stat_name)
-	local m = self:measure(stat_name or event_name, "times");
-	local function handler(handlers, _event_name, _event_data)
-		local finished = m();
-		local ret = handlers(_event_name, _event_data);
-		finished();
-		return ret;
+function api:metric(type_, name, unit, description, label_keys, conf)
+	local metric = require "core.statsmanager".metric;
+	local is_scoped = self.host ~= "*"
+	if is_scoped then
+		-- prepend `host` label to label keys if this is not a global module
+		local orig_labels = label_keys
+		label_keys = array { "host" }
+		label_keys:append(orig_labels)
 	end
-	return self:hook_object_event(events_object, event_name, handler);
-end
-
-function api:measure_event(event_name, stat_name)
-	return self:measure_object_event((hosts[self.host] or prosody).events.wrappers, event_name, stat_name);
-end
-
-function api:measure_global_event(event_name, stat_name)
-	return self:measure_object_event(prosody.events.wrappers, event_name, stat_name);
+	local mf = metric(type_, "prosody_mod_"..self.name.."/"..name, unit, description, label_keys, conf)
+	if is_scoped then
+		-- make sure to scope the returned metric family to the current host
+		return mf:with_partial_label(self.host)
+	end
+	return mf
 end
 
 local status_priorities = { error = 3, warn = 2, info = 1, core = 0 };