Allow restricting exporter scope to specific instances

[mindw]

Is your feature request related to a problem? Please describe.

I'm looking for exporting the output of describe-db-instances to prometheus. This promising project seems to fit the bill - except it returns metrics for all RDS instances within region. At least I could not an example on how to do it.

Describe the solution you'd like

Add an option to restrict exporter to an RDS instance(s) by - id, regex, tag (key/*, key/val, key/regex)

Describe alternatives you've considered

Use the archived https://github.com/movio/aws-prometheus-exporter exporter to expose describe-db-instances output.

Thanks!

[vmercierfr]

Thanks for reporting this issue. In our initial use case, we needed to collect metrics from all RDS instances, but it makes sense to support instance filtering. We need to think about the way to implement it.

Can you provide more details on your ideal instance filters (e.g., on which RDS instance parameters you would like to filter)? If you can provide a concrete use case, it will help us a lot to design the feature.

---

Meanwhile, I see two possible workarounds:

• Use the rds_instance_tags metric (introduced in v0.5.0 for a similar issue Add RDS tags #37) to filter Prometheus results, but metrics are still collected and stored in your Prometheus

• Use metric_relabel_configs Prometheus parameter to drop useless metrics, but metrics are still fetched from AWS APIs

  scrape_configs:
    - job_name: 'rds-exporter'
      static_configs:
        - targets: ['rds-exporter:9043']
      metric_relabel_configs:
        - source_labels: [job, dbidentifier]
          separator: "@"
          regex: "rds-exporter@db[0-9]+" # Exclude all metrics collected by "rds-exporter" job that match "db[0-9]+" regexp
          action: drop

[mindw]

@vmercierfr thanks you for looking into this and the prompt reply!

For my use case filtering on a specific identifier is sufficient. Something like a db-instance key in the config accepting a single value.

The rest of the options I've picked up from CloudWatch exporter filters.

[vmercierfr]

I guess jstewart612 is also interested by this feature.