[Tile-serving] [openstreetmap/mod_tile] Add a Prometheus metrics endpoint (#222)

[Tom Hughes]

This is an example response from our current ruby script, which should be similar to what this patch produces:

```
# HELP modtile_http_response_total Number of HTTP responses by response code
# TYPE modtile_http_response_total counter
modtile_http_response_total{code="200"} 47092130
modtile_http_response_total{code="304"} 28129640
modtile_http_response_total{code="404"} 6234
modtile_http_response_total{code="503"} 0
modtile_http_response_total{code="5XX"} 0
modtile_http_response_total{code="other"} 0
# HELP modtile_tile_total Number of tiles served
# TYPE modtile_tile_total counter
modtile_tile_total{age="fresh",rendered="no"} 70984024
modtile_tile_total{age="old",rendered="no"} 0
modtile_tile_total{age="outdated",rendered="no"} 0
modtile_tile_total{age="fresh",rendered="yes"} 3919472
modtile_tile_total{age="old",rendered="attempted"} 685
modtile_tile_total{age="outdated",rendered="attempted"} 318023
# HELP modtile_zoom_tile_total Number of tiles served by zoom level
# TYPE modtile_zoom_tile_total counter
modtile_zoom_tile_total{zoom="0"} 14
modtile_zoom_tile_total{zoom="1"} 1295
modtile_zoom_tile_total{zoom="2"} 37
modtile_zoom_tile_total{zoom="3"} 132
modtile_zoom_tile_total{zoom="4"} 292
modtile_zoom_tile_total{zoom="5"} 707
modtile_zoom_tile_total{zoom="6"} 1778
modtile_zoom_tile_total{zoom="7"} 1437
modtile_zoom_tile_total{zoom="8"} 3983
modtile_zoom_tile_total{zoom="9"} 11765
modtile_zoom_tile_total{zoom="10"} 17676
modtile_zoom_tile_total{zoom="11"} 29349
modtile_zoom_tile_total{zoom="12"} 35724
modtile_zoom_tile_total{zoom="13"} 5000429
modtile_zoom_tile_total{zoom="14"} 7278472
modtile_zoom_tile_total{zoom="15"} 10788637
modtile_zoom_tile_total{zoom="16"} 13310500
modtile_zoom_tile_total{zoom="17"} 16435153
modtile_zoom_tile_total{zoom="18"} 14647665
modtile_zoom_tile_total{zoom="19"} 7656725
# HELP modtile_read_count_total Number of tiles read from disk
# TYPE modtile_read_count_total counter
modtile_read_count_total 75221629
# HELP modtile_read_seconds_total Number of seconds spend reading from disk
# TYPE modtile_read_seconds_total counter
modtile_read_seconds_total 26845.23321
# HELP modtile_zoom_read_count_total Number of tiles read from disk by zoom level
# TYPE modtile_zoom_read_count_total counter
modtile_zoom_read_count_total{zoom="0"} 14
modtile_zoom_read_count_total{zoom="1"} 1295
modtile_zoom_read_count_total{zoom="2"} 37
modtile_zoom_read_count_total{zoom="3"} 132
modtile_zoom_read_count_total{zoom="4"} 292
modtile_zoom_read_count_total{zoom="5"} 707
modtile_zoom_read_count_total{zoom="6"} 1778
modtile_zoom_read_count_total{zoom="7"} 1437
modtile_zoom_read_count_total{zoom="8"} 3983
modtile_zoom_read_count_total{zoom="9"} 11765
modtile_zoom_read_count_total{zoom="10"} 17676
modtile_zoom_read_count_total{zoom="11"} 29349
modtile_zoom_read_count_total{zoom="12"} 35724
modtile_zoom_read_count_total{zoom="13"} 5000419
modtile_zoom_read_count_total{zoom="14"} 7278465
modtile_zoom_read_count_total{zoom="15"} 10788629
modtile_zoom_read_count_total{zoom="16"} 13310476
modtile_zoom_read_count_total{zoom="17"} 16435117
modtile_zoom_read_count_total{zoom="18"} 14647638
modtile_zoom_read_count_total{zoom="19"} 7656696
# HELP modtile_zoom_read_seconds_total Number of seconds spend reading from disk by zoom level
# TYPE modtile_zoom_read_seconds_total counter
modtile_zoom_read_seconds_total{zoom="0"} 0.001955
modtile_zoom_read_seconds_total{zoom="1"} 0.060303
modtile_zoom_read_seconds_total{zoom="2"} 0.006941
modtile_zoom_read_seconds_total{zoom="3"} 0.116287
modtile_zoom_read_seconds_total{zoom="4"} 0.083617
modtile_zoom_read_seconds_total{zoom="5"} 0.419832
modtile_zoom_read_seconds_total{zoom="6"} 0.656725
modtile_zoom_read_seconds_total{zoom="7"} 1.017994
modtile_zoom_read_seconds_total{zoom="8"} 1.506264
modtile_zoom_read_seconds_total{zoom="9"} 3.766258
modtile_zoom_read_seconds_total{zoom="10"} 5.725569
modtile_zoom_read_seconds_total{zoom="11"} 9.74763
modtile_zoom_read_seconds_total{zoom="12"} 13.866226
modtile_zoom_read_seconds_total{zoom="13"} 1762.651592
modtile_zoom_read_seconds_total{zoom="14"} 2828.137942
modtile_zoom_read_seconds_total{zoom="15"} 4257.89612
modtile_zoom_read_seconds_total{zoom="16"} 5290.864963
modtile_zoom_read_seconds_total{zoom="17"} 5894.000526
modtile_zoom_read_seconds_total{zoom="18"} 4993.436004
modtile_zoom_read_seconds_total{zoom="19"} 1781.270462
```

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/mod_tile/pull/222#issuecomment-787207084
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20210227/3ac5f463/attachment-0001.htm>