feat: The Prometheus plugin can now allow users to configure the DEFAULT_BUCKETS

[wklken]

Description

-- Default set of latency buckets, 1ms to 60s:
local DEFAULT_BUCKETS = {1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000, 30000, 60000}

3 types: apisix/request/upstream

If we have 10,000 routes, the maximum number of metrics can be (15+1) * 3 * 10000 = 480,000, which is a huge response. (we will deploy 1 route to multiple services, so it will be much more records than that)

In production, we may not need such accurate metrics and can instead set them to {50, 100, 200, 500, 1000, 5000}, so it only have 210,000 metrics.

Or if we do not need the metrics by default, we can set it to {100000} to make the response small enough.(we registerd our own metrics)

Is it possible to set the buckets via plugin_attr? or can we add some triggers for those default metrics.

plugin_attr:
  prometheus:
    default_buckets:
      - 50
      - 100
      - 200
      - 500

[shreemaan-abhishek]

@kingluo what do you think?

[kingluo]

Yes, I think it's better to be configurable.

[jiangfucheng]

Hi, I want try to implement this feature, could assign it to me?