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132 lines
4 KiB
Markdown
132 lines
4 KiB
Markdown
# FSM Mapping
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## Overview
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This package implements a fast and efficient algorithm for generic glob style
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string matching using a finite state machine (FSM).
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### Source Hierachy
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```
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'-- fsm
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'-- dump.go // functionality to dump the FSM to Dot file
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'-- formatter.go // format glob templates using captured * groups
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'-- fsm.go // manipulating and searching of FSM
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'-- minmax.go // min() max() function for interger
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```
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## FSM Explained
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Per [Wikipedia](https://en.wikipedia.org/wiki/Finite-state_machine):
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> A finite-state machine (FSM) or finite-state automaton (FSA, plural: automata),
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> finite automaton, or simply a state machine, is a mathematical model of
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> computation. It is an abstract machine that can be in exactly one of a finite
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> number of states at any given time. The FSM can change from one state to
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> another in response to some external inputs; the change from one state to
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> another is called a transition. An FSM is defined by a list of its states, its
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> initial state, and the conditions for each transition.
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In our use case, each *state* is a substring after the input StatsD metric name is splitted by `.`.
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### Add state to FSM
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`func (f *FSM) AddState(match string, matchMetricType string,
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maxPossibleTransitions int, result interface{}) int`
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At first, the FSM only contains three states, representing three possible metric types:
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____ [gauge]
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/
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(start)---- [counter]
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\
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'--- [observer]
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Adding a rule `client.*.request.count` with type `counter` will make the FSM to be:
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____ [gauge]
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/
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(start)---- [counter] -- [client] -- [*] -- [request] -- [count] -- {R1}
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\
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'--- [observer]
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`{R1}` is short for result 1, which is the match result for `client.*.request.count`.
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Adding a rule `client.*.*.size` with type `counter` will make the FSM to be:
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____ [gauge] __ [request] -- [count] -- {R1}
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/ /
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(start)---- [counter] -- [client] -- [*]
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\ \__ [*] -- [size] -- {R2}
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'--- [observer]
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### Finding a result state in FSM
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`func (f *FSM) GetMapping(statsdMetric string, statsdMetricType string)
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(*mappingState, []string)`
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For example, when mapping `client.aaa.request.count` with `counter` type in the
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FSM, the `^1` to `^7` symbols indicate how FSM will traversal in its tree:
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____ [gauge] __ [request] -- [count] -- {R1}
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/ / ^5 ^6 ^7
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(start)---- [counter] -- [client] -- [*]
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^1 \ ^2 ^3 \__ [*] -- [size] -- {R2}
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'--- [observer] ^4
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To map `client.bbb.request.size`, FSM will do a backtracking:
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____ [gauge] __ [request] -- [count] -- {R1}
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/ / ^5 ^6
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(start)---- [counter] -- [client] -- [*]
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^1 \ ^2 ^3 \__ [*] -- [size] -- {R2}
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'--- [observer] ^4
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^7 ^8 ^9
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## Debugging
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To see all the states of the current FSM, use `func (f *FSM) DumpFSM(w io.Writer)`
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to dump into a Dot file. The Dot file can be further renderer into image using:
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```shell
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$ dot -Tpng dump.dot > dump.png
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```
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In StatsD exporter, one could use the following:
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```shell
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$ statsd_exporter --statsd.mapping-config=statsd.rules --debug.dump-fsm=dump.dot
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$ dot -Tpng dump.dot > dump.png
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```
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For example, the following rules:
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```yaml
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mappings:
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- match: client.*.request.count
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name: request_count
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match_metric_type: counter
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labels:
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client: $1
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- match: client.*.*.size
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name: sizes
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match_metric_type: counter
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labels:
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client: $1
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direction: $2
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```
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will be rendered as:
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The `dot` program is part of [Graphviz](https://www.graphviz.org/) and is
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available in most of popular operating systems.
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