Current state

 Basic matrics more expensive then enhanced metrics.
CloudWatch Logs are not always available, too, for cost or other reasons.

DoD

We should allow users to disable basic and/or enhanced metrics when RDS instance is added. That feature should be available via API and Add RDS Instance UI (as an additional checkbox).

Implementation

rds_exporter

• Add disable_basic_metrics, disable_enhanced_metrics fields to per-instance configuration.
• Do not check session and start scraper for that instance if metrics are disabled.
• Both /basic and /enhanced endpoints / Prometheus registries should still be available even if basic and enhanced metrics are disabled for all instances in the configuration.

API

• Inventory API: add flags disable_basic_metrics, disable_enhanced_metrics to RDSExporter;
• Inventory API: add flags basic_metrics_disabled, enhanced_metrics_disabled to AddRDSExporterRequest;
• Management API: add flags disable_basic_metrics, disable_enhanced_metrics to AddRDSRequest.

pmm-managed

• Add rds_basic_metrics_disabled, rds_enhanced_metrics_disabled fields into Agent model.
• Accept, save, and return those fields in all APIs.
• Include those fields in rds_exporter configuration for pmm-agent.
• Still always add /basic and /enhanced endpoints to Prometheus configuration even if all metrics are disabled.

pmm-admin

• Add flags disable-basic-metrics, disable-enhanced-metrics into pmm-admin inventory add agent rds-exporter command.
• There is no management command to add RDS instance, so nothing should be done for management commands.

UI

• Add two checkboxes on add RDS instance page / section .

DOC

• we MUST explain flags in our documentation

Discussion

• All flags and fields are called "disable"/"disabled" instead of "enable"/"enabled" to play nicely with Go and protobuf default values for booleans, and for backward compatibility.
• The ability to change enable/disable enhanced/basic metrics without removing and re-adding RDS instance (or just rds_exporter via Inventory API) is not in scope. No changes in ChangeRDSExporter Inventory API.
• Refactoring Agent model in pmm-managed to merge several different fields (query_examples_disabled, max_query_log_size, basic_metrics_disabled, etc) into a single JSON field is a separate ticket: PMM-5086
• Combining basic and enhanced metrics in a single endpoint is a separate ticket: PMM-1901
• Automatic detection of whatever basic and enhanced metrics should be enabled is out-of-scope. roma.novikov will create a separate ticket.