[DO NOT MERGE]Add environment variables for stats config (#1627)

[rg2011]

Adds environment variables for stats configuration (fixes #1627).

NOTE: Adds documentation for config.stats.persistence, that seemed to be undocumented.

NOTE: Changed to DO NOT MERGE because of #1627 (comment)

[fgalan]

It would be great to provide more detail on this. For instance:

• In which collection at mongo backend are the stas persisted?
• How are the documents in that collection? Which fields they have? An example would be also great

[rg2011]

fixed

[AlvaroVega]

@rg2011 Is this PR including all feature? if feature is already implemented any link to paths involved or doc related is welcome!

[rg2011]

@rg2011 Is this PR including all feature? if feature is already implemented any link to paths involved or doc related is welcome!

The stats.persistence flag and kpis mongo collection were actually added in commit fd1354b 9 years ago (!?).

So the feature was already present, this PR only exposes its configuration through environment variables.

I also added some documentation for the stats.persistence parameter that I dind't find mentioned elsewhere, the documentation I wrote was derived from the code in:

• iotagent-node-lib/lib/model/dbConn.js

  Lines 193 to 196 in 01b3f5f

  	if (
  	(currentConfig.deviceRegistry && currentConfig.deviceRegistry.type === 'mongodb') ||
  	(currentConfig.stats && currentConfig.stats.persistence === true)
  	) {

  : Creates a dbConn if stats.persistence is true

• iotagent-node-lib/lib/services/stats/statsRegistry.js

  Lines 179 to 184 in 01b3f5f

  	function mongodbPersistence(currentValues, globalValues, callback) {
  	const statStamp = _.clone(globalValues);
  	statStamp.timestamp = new Date().toISOString();
  	dbService.db.collection('kpis').insertOne(statStamp, callback);
  	}

  : Uses collection kpis for stats, dumps global stats as mongo document.

However, it seems that setting stats.persistence is not enough to enable stats persistence. activateStatLogs does not check the flag at all, and will never schedule the mongodbPersistence action:

iotagent-node-lib/lib/fiware-iotagent-lib.js

Lines 48 to 64 in 01b3f5f

	function activateStatLogs(newConfig, callback) {
	if (newConfig.stats && newConfig.stats.interval) {
	async.series(
	[
	apply(statsRegistry.globalLoad, {
	deviceCreationRequests: 0,
	deviceRemovalRequests: 0,
	measureRequests: 0
	}),
	apply(statsRegistry.addTimerAction, statsRegistry.logStats)
	],
	callback
	);
	} else {
	callback();
	}
	}

So if an user wants stats persisted to mongo , in addition to defining stats.persistence, it must also schedule an statsRegistry.addTimerAction(statsRegistry.mongodbPersistence, ...) as done here:

iotagent-node-lib/test/unit/general/statistics-persistence_test.js

Line 104 in 01b3f5f

statsService.addTimerAction(statsService.mongodbPersistence, function () {

I will add this to the documentation.

[rg2011]

I will add this to the documentation.

0bb40cd

[AlvaroVega]

The stats.persistence flag and kpis mongo collection were actually added in commit fd1354b 9 years ago (!?).

So the feature was already present, this PR only exposes its configuration through environment variables.

OMG! I'm pretty sure nobody has used this feature before, so I'm not sure if is fully implemented. Let's see.

[rg2011]

deprecated by #1629