Feature Request: Lightweight CNCLI Blocks Prometheus Exporter

[Straightpool]

Feature description
A lightweight Prometheus exporter for the CNCLI "Blocks" data.
I propose the following metrics, always in relation to the current active epoch for monitoring purposes:

• cntools_cncli_blocks_metrics_next_leader_time_utc
• cntools_cncli_blocks_metrics_next_next_leader_time_utc
• cntools_cncli_blocks_metrics_ideal
• cntools_cncli_blocks_metrics_luck
• cntools_cncli_blocks_metrics_adopted_total
• cntools_cncli_blocks_metrics_confirmed_total
• cntools_cncli_blocks_metrics_missed_total
• cntools_cncli_blocks_metrics_ghosted_total
• cntools_cncli_blocks_metrics_stolen_total
• cntools_cncli_blocks_metrics_invalid_total
• cntools_cncli_blocks_metrics_adopted_max_consec
• cntools_cncli_blocks_metrics_confirmed_max_consec
• cntools_cncli_blocks_metrics_missed_max_consec
• cntools_cncli_blocks_metrics_ghosted_max_consec
• cntools_cncli_blocks_metrics_stolen_max_consec
• cntools_cncli_blocks_metrics_invalid_max_consec

Next_leader_time_UTC returns the UTC time of the next leader slot
Next_next_leader_time_UTC returns the UTC time of the leader slot after next

*_total refers to the total number at the current time. *_max_consec refers to the max consecutive occurrence of said block state.

Example
Example block sequence:

1. confirmed
2. confirmed
3. stolen
4. confirmed
5. ghosted
6. confirmed
7. confirmed
8. confirmed
9. missed
10. confirmed
11. confirmed
12. confirmed
13. confirmed
14. missed
15. missed
16. missed
17. invalid

Results in:

• cntools_cncli_blocks_metrics_adopted_total: 0
• cntools_cncli_blocks_metrics_confirmed_total: 10
• cntools_cncli_blocks_metrics_missed_total: 4
• cntools_cncli_blocks_metrics_ghosted_total: 1
• cntools_cncli_blocks_metrics_stolen_total: 1
• cntools_cncli_blocks_metrics_invalid_total: 1
• cntools_cncli_blocks_metrics_adopted_max_consec: 0
• cntools_cncli_blocks_metrics_confirmed_max_consec: 4
• cntools_cncli_blocks_metrics_missed_max_consec: 3
• cntools_cncli_blocks_metrics_ghosted_max_consec: 1
• cntools_cncli_blocks_metrics_stolen_max_consec: 1
• cntools_cncli_blocks_metrics_invalid_max_consec: 1

Rationale
Sometimes out of the blue errors or bugs can occur in the pool infrastructure or Cardano node itself which can lead to a number of consecutive lost blocks. A single missed block is currently usually a false classification and rather a ghosted block. A single ghosted block is usually a race condition currently.
However, if any of these error states do happen in multiples in direct succession something is clearly off though and ought to trigger an alert / action based on Prometheus / Grafana rules. In the example "cntools_cncli_blocks_metrics_missed_max_consec: 3" would be such a case which would warrant an alert / action or cntools_cncli_blocks_metrics_invalid_total =! 0. Without a Prometheus Exporter it might take a while to notice the issue, especailly if it triggers no other alerts, with more lost blocks than necessary.

Possible implementation approaches
From first looks this seems to be a feasible architecture with SQL scraping:

• Build upon an open source extensible sql-query Prometheus exporter such as: https://github.com/albertodonato/query-exporter
• To determine consecutive runs a SQL count partition query should deliver expected results, see e.g. https://stackoverflow.com/questions/36927685/count-number-of-consecutive-occurrence-of-values-in-table

Another approach could be to use Bash pushing:

• Employ a Prometheus PushGateway to use Bash scripts to push an update when there is an update on a block, see e.g. https://medium.com/avmconsulting-blog/pushing-bash-script-result-to-prometheus-using-pushgateway-a0760cd261e
• See https://prometheus.io/docs/practices/pushing/ on the implications

Considered alternatives
None

Version:

• OS: Ubunto 20.04 LTS
• Product version: CNTools 9.1.0
• Cardano Node version:
  cardano-node 1.34.1 - linux-x86_64 - ghc-8.10
  git rev 73f9a746362695dc2cb63ba757fbcabb81733d23
• Network you're connecting to: Mainnet