[Telemetry] Share promise for concurrent telemetry report generation

[afharo]

As identified in the Load Testing PR elastic/kibana-load-testing#211, we could improve the performance of Kibana if we'd handle concurrent Telemetry Report Generation together in one promise.

This way, if a new request comes in while the Report Generation is taking place due to a previous request, they'll await the same promise. This way we'll reduce the load on both ES and Kibana, and it will reduce response times for any new incoming request.

Once it's served, the caching mechanism that's already in place, will ensure that we don't generate the report again for a few hours (currently 4h).

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[pgayvallet]

Mind sharing a few pointers regarding where the reports are generated from?

[afharo]

Good point! We generate the report here:

kibana/src/plugins/telemetry_collection_manager/server/plugin.ts

Lines 245 to 284 in d12c1e8

	private async getStats(config: StatsGetterConfig) {
	if (!this.usageCollection) {
	return [];
	}
	const collection = this.collectionStrategy;
	if (collection) {
	// Build the context (clients and others) to send to the CollectionStrategies
	const statsCollectionConfig = this.getStatsCollectionConfig(config, this.usageCollection);
	if (statsCollectionConfig) {
	try {
	const usageData = await this.getUsageForCollection(collection, statsCollectionConfig);
	this.logger.debug(`Received Usage using ${collection.title} collection.`);
	return await Promise.all(
	usageData.map(async (clusterStats) => {
	const { cluster_uuid: clusterUuid } = clusterStats.cluster_stats as Record<
	string,
	string
	>;
	return {
	clusterUuid,
	stats: config.unencrypted
	? clusterStats
	: await encryptTelemetry(clusterStats, {
	useProdKey: this.isDistributable,
	}),
	};
	})
	);
	} catch (err) {
	this.logger.debug(
	`Failed to collect any usage with registered collection ${collection.title}.`
	);
	}
	}
	}
	return [];
	}

[afharo]

I think that it will be easier if we implement #96538 first. Because we can share the response to all users and do not bear in mind the permissions of each one of them.

[afharo]

Grooming outcome: we are closing this as we think the improvement will only cover a very niche scenario. Especially after all the improvements we've done in the report generation after we created this issue.