Expose Kibana settings needed by Monitoring via HTTP API

[ycombinator]

In the same vein as #20577, Kibana should provide an HTTP API that exposes Kibana settings currently used by Kibana X-Pack Monitoring. I believe the only such setting today is the admin email address.

Use case

Metricbeat — concretely the settings metricset in the kibana module — will call this API periodically and ship the results in the right format to .kibana-monitoring-6-* indices. This will help make progress towards completing the larger feature of using Metricbeat to monitoring Kibana (and eventually the rest of the Elastic stack).

Important note

This API is likely a temporary solution until the Kibana Alerting feature is built. Once that is shipped and driving the Cluster Alerts feature in Monitoring, we will no longer need to index kibana_settings documents into .kibana-monitoring-6* indices. At that point this API (and the corresponding metricset in metricbeat) can be removed. As such it is probably best to not document this API for external/public use.

[ycombinator]

Proposal for API

I looked at a sample document from .kibana-monitoring-6-* with type = kibana_settings. Here's what it looks like:

{
  "cluster_uuid":"u5ii0pnQRka_P0gimfmthg",
  "timestamp":"2018-07-03T17:17:02.356Z",
  "interval_ms":10000,
  "type":"kibana_settings",
  "source_node":{
    "uuid":"Txan2CYoQeCvDfkBm4lpRw",
    "host":"127.0.0.1",
    "transport_address":"127.0.0.1:9300",
    "ip":"127.0.0.1",
    "name":"Txan2CY",
    "timestamp":"2018-07-03T17:17:02.356Z"
  },
  "kibana_settings":{
    "xpack":{
      "default_admin_email":"jane@doe.com"
    },
    "kibana":{
      "uuid":"5b2de169-2785-441b-ae8c-186a1936b17d",
      "name":"Janes-MBP-2",
      "index":".kibana",
      "host":"localhost",
      "transport_address":"localhost:5601",
      "version":"7.0.0-alpha1",
      "snapshot":false,
      "status":"green"
    }
  }
}

Based on the information within it, here's my proposal for a minimal Kibana settings HTTP API.

URL

GET /api/settings

(This mirrors the GET /api/stats API URL built in #20577).

Response structure

{
  "cluster_uuid":"u5ii0pnQRka_P0gimfmthg",
  "settings":{
    "xpack":{
      "default_admin_email":"jane@doe.com"
    },
    "kibana":{
      "uuid":"5b2de169-2785-441b-ae8c-186a1936b17d",
      "name":"Janes-MBP-2",
      "index":".kibana",
      "host":"localhost",
      "transport_address":"localhost:5601",
      "version":"7.0.0-alpha1",
      "snapshot":false,
      "status":"green"
    }
  }
}

WDYT?