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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

local hashring = require "util.hashring";

describe("util.hashring", function ()

	local sha256 = require "util.hashes".sha256;

	local ring = hashring.new(128, sha256);

	it("should fail to get a node that does not exist", function ()
		assert.is_nil(ring:get_node("foo"))
	end);

	it("should support adding nodes", function ()
		ring:add_node("node1");
	end);

	it("should return a single node for all keys if only one node exists", function ()
		for i = 1, 100 do
			assert.is_equal("node1", ring:get_node(tostring(i)))
		end
	end);

	it("should support adding a second node", function ()
		ring:add_node("node2");
	end);

	it("should fail to remove a non-existent node", function ()
		assert.is_falsy(ring:remove_node("node3"));
	end);

	it("should succeed to remove a node", function ()
		assert.is_truthy(ring:remove_node("node1"));
	end);

	it("should return the only node for all keys", function ()
		for i = 1, 100 do
			assert.is_equal("node2", ring:get_node(tostring(i)))
		end
	end);

	it("should support adding multiple nodes", function ()
		ring:add_nodes({ "node1", "node3", "node4", "node5" });
	end);

	it("should disrupt a minimal number of keys on node removal", function ()
		local orig_ring = ring:clone();
		local node_tallies = {};

		local n = 1000;

		for i = 1, n do
			local key = tostring(i);
			local node = ring:get_node(key);
			node_tallies[node] = (node_tallies[node] or 0) + 1;
		end

		--[[
		for node, key_count in pairs(node_tallies) do
			print(node, key_count, ("%.2f%%"):format((key_count/n)*100));
		end
		]]

		ring:remove_node("node5");

		local disrupted_keys = 0;
		for i = 1, n do
			local key = tostring(i);
			if orig_ring:get_node(key) ~= ring:get_node(key) then
				disrupted_keys = disrupted_keys + 1;
			end
		end
		assert.is_equal(node_tallies["node5"], disrupted_keys);
	end);

	it("should support removing multiple nodes", function ()
		ring:remove_nodes({"node2", "node3", "node4", "node5"});
	end);

	it("should return a single node for all keys if only one node remains", function ()
		for i = 1, 100 do
			assert.is_equal("node1", ring:get_node(tostring(i)))
		end
	end);

end);