Additional Prometheus metrics

[gabrieltz]

Hello,

It would be nice to have some additional prometheus metrics that already exist in /stats endpoint:

1. lastUpdate exposed as a gauge with seconds since last update, or unix timestamp to detect if something is not "feeding meilisearch with new data" so we can define alert rules to prevent stale data.
2. isIndexing exposed as 0/1 would be helpful to correlate slower http_response_time_seconds_bucket with indexing

and from the /tasks endpoint

1. exposing the number of tasks with queued status ( gauge )
2. exposing the number of tasks with processing status ( gauge )

thank you

[macraig]

Hi @gabrieltz , thanks for taking the time to leave your feedback! I'll move it to #625 and close this so we can keep all the Prometheus metrics under the same discussion. Feel free to add to that discussion as well!

[gabrieltz]

thank you @macraig , i'll keep an eye on the discussion there