I like this, but not at the expense of JSON output. It would be the only
new API surface for CouchDB that isn't JSON-based, and there needs to be
excellent justification for such. Prometheus is well-known enough to be
supported, but we should continue to put out JSON stats for the
foreseeable future.
I know that Prometheus can't send a header, but sending an accepts
application/json to /_metrics and having it send back the same data as
Prometheus, but in JSON, would be lovely. If you feel up to it :)
-Joan "on vacation" Touzet
On 2020-09-22 8:55 a.m., jiangph wrote:
Hey all,
We would like to add a Prometheus metrics endpoint for CouchDB and wanted to
see if the community would be interested in us contributing this to CouchDB 4.x.
Prometheus is a CNCF open-source project and the Prometheus metrics endpoint
format is supported by many monitoring tools. Its data model is based around
having a metric name which then contains a label name and a label value:
<metric name>{<label name>=<label value>, ...}
And it supports the Counter, Gauge, Histogram, and Summary metric types.
The idea for the new Prometheus endpoint, /_metrics, would be that the endpoint
is a consolidation of the _stats [1], _system [2], and _active_tasks [3]
endpoints.
For _stats and _system, the conversion from JSON to Prometheus-based format
seems to be straightforward.
JSON format:
{
"value": {
"min": 0,
"max": 0,
"arithmetic_mean": 0,
"geometric_mean": 0,
"harmonic_mean": 0,
"median": 0,
"variance": 0,
"standard_deviation": 0,
...
"percentile": [
[
50,
0
],
[
75,
0
],
[
90,
0
],
[
95,
0
],
[
99,
0
],
[
999,
0
]
],
"histogram": [
[
0,
0
]
],
}
Prometheus-based format:
couchdb_stats{value="min"} 0
couchdb_stats{value="max"} 0
couchdb_stats{value="percentile50"} 0
couchdb_stats{value="percentile75"} 0
couchdb_stats{value="percentile95"} 0
For _active_tasks, the change will be a bit more complicated, and some fields
will be added to labels and tags.
JSON format:
{
"checkpointed_source_seq": 68585,
"continuous": false,
"doc_id": null,
"doc_write_failures": 0,
"docs_read": 4524,
"docs_written": 4524,
"missing_revisions_found": 4524,
"pid": "<0.1538.5>",
"progress": 44,
"replication_id": "9bc1727d74d49d9e157e260bb8bbd1d5",
"revisions_checked": 4524,
"source": "mailbox",
"source_seq": 154419,
"started_on": 1376116644,
"target": "http://mailsrv:5984/mailbox <http://mailsrv:5984/mailbox>",
"type": "replication",
"updated_on": 1376116651
}
Prometheus-based would look something like:
format:couchdb_active_task{type="replication", source="mailbox", target="http://mailsrv:5984/mailbox
<http://mailsrv:5984/mailbox>", docs_count = "docs_read"} 4524
couchdb_active_task{type="replication", source="mailbox", target="http://mailsrv:5984/mailbox
<http://mailsrv:5984/mailbox>", docs_count = "docs_written"} 4524
couchdb_active_task{type="replication", source="mailbox", target="http://mailsrv:5984/mailbox
<http://mailsrv:5984/mailbox>", docs_count = "missing_revisions_found"} 4524
Best regards,
Garren Smith
Peng Hui Jiang
[1] https://docs.couchdb.org/en/latest/api/server/common.html#node-node-name-stats
<https://docs.couchdb.org/en/latest/api/server/common.html#node-node-name-stats>
[2] https://docs.couchdb.org/en/latest/api/server/common.html#active-tasks
<https://docs.couchdb.org/en/latest/api/server/common.html#active-tasks>
[3] https://docs.couchdb.org/en/latest/api/server/common.html#node-node-name-system
<https://docs.couchdb.org/en/latest/api/server/common.html#node-node-name-system>
