GET /_nodes/http,settings?flat_settings returns path.data as an array of strings

[russcam]

Elasticsearch version (bin/elasticsearch --version): 6.1.0

Plugins installed: []

JVM version (java -version):

java version "1.8.0_144"
Java(TM) SE Runtime Environment (build 1.8.0_144-b01)
Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

OS version (uname -a if on a Unix-like system): Windows 10

Description of the problem including expected versus actual behavior:

The .NET client (as well as other clients) uses

GET /_nodes/http,settings?flat_settings

to sniff the state of the cluster. With Elasticsearch 6.0.1, the response looks like

{
    "_nodes": {
        "total": 1,
        "successful": 1,
        "failed": 0
    },
    "cluster_name": "sniffroledetection-cluster-2ba8fa",
    "nodes": {
        "U_ztq5UiS2e8xyOjL_evlA": {
            "name": "sniffroledetection-node-2ba8fa",
            "transport_address": "127.0.0.1:9300",
            "host": "127.0.0.1",
            "ip": "127.0.0.1",
            "version": "6.0.1",
            "build_hash": "601be4a",
            "roles": ["master", "ingest"],
            "attributes": {
                "testingcluster": "true",
                "ml.max_open_jobs": "10",
                "rack_id": "rack_one",
                "ml.enabled": "true",
                "gateway": "true"
            },
            "settings": {
                "client.type": "node",
                "cluster.name": "sniffroledetection-cluster-2ba8fa",
                "http.port": "9200",
                "http.type.default": "netty4",
                "node.attr.gateway": "true",
                "node.attr.ml.enabled": "true",
                "node.attr.ml.max_open_jobs": "10",
                "node.attr.rack_id": "rack_one",
                "node.attr.testingcluster": "true",
                "node.data": "false",
                "node.master": "true",
                "node.name": "sniffroledetection-node-2ba8fa",
                "path.data.0": "C:\\Users\\User\\AppData\\Roaming\\NEST\\6.0.1\\elasticsearch-6.0.1\\data\\sniffroledetection-cluster-2ba8fa",
                "path.home": "C:\\Users\\User\\AppData\\Roaming\\NEST\\6.0.1\\elasticsearch-6.0.1",
                "path.logs": "C:\\Users\\User\\AppData\\Roaming\\NEST\\6.0.1\\elasticsearch-6.0.1\\logs",
                "path.repo": "C:\\Users\\User\\AppData\\Roaming\\NEST\\6.0.1\\repositories",
                "script.allowed_types": "inline,stored",
                "script.max_compilations_rate": "10000/1m",
                "search.remote.connect": "true",
                "transport.type.default": "netty4",
                "xpack.notification.hipchat.account.notify-monitoring.profile": "user",
                "xpack.notification.hipchat.account.notify-monitoring.user": "watcher-user@example.com",
                "xpack.security.authc.realms.file1.order": "0",
                "xpack.security.authc.realms.file1.type": "file",
                "xpack.security.authc.realms.pki1.enabled": "false",
                "xpack.security.authc.realms.pki1.order": "1",
                "xpack.security.authc.realms.pki1.type": "pki",
                "xpack.security.enabled": "false",
                "xpack.security.http.ssl.enabled": "false"
            },
            "http": {
                "bound_address": ["127.0.0.1:9200", "[::1]:9200"],
                "publish_address": "127.0.0.1:9200",
                "max_content_length_in_bytes": 104857600
            }
        }
    }
}

where path.data are flattened into individual key/value string pairs.

With Elasticsearch 6.1.0 however, the response is

{
  "_nodes": {
    "total": 1,
    "successful": 1,
    "failed": 0
  },
  "cluster_name": "sniffroledetection-cluster-4fc5bf",
  "nodes": {
    "VNm0VsLrT1WgF29TePLTgQ": {
      "name": "sniffroledetection-node-4fc5bf",
      "transport_address": "127.0.0.1:9300",
      "host": "127.0.0.1",
      "ip": "127.0.0.1",
      "version": "6.1.0",
      "build_hash": "c0c1ba0",
      "roles": ["master", "ingest"],
      "attributes": {
        "testingcluster": "true",
        "rack_id": "rack_one",
        "ml.machine_memory": "16944017408",
        "ml.max_open_jobs": "20",
        "ml.enabled": "true",
        "gateway": "true"
      },
      "settings": {
        "client.type": "node",
        "cluster.name": "sniffroledetection-cluster-4fc5bf",
        "http.port": "9200",
        "http.type.default": "netty4",
        "node.attr.gateway": "true",
        "node.attr.ml.enabled": "true",
        "node.attr.ml.machine_memory": "16944017408",
        "node.attr.ml.max_open_jobs": "20",
        "node.attr.rack_id": "rack_one",
        "node.attr.testingcluster": "true",
        "node.data": "false",
        "node.master": "true",
        "node.name": "sniffroledetection-node-4fc5bf",
        "path.data": ["C:\\Users\\russc\\AppData\\Roaming\\NEST\\6.1.0\\elasticsearch-6.1.0\\data\\sniffroledetection-cluster-4fc5bf"],
        "path.home": "C:\\Users\\russc\\AppData\\Roaming\\NEST\\6.1.0\\elasticsearch-6.1.0",
        "path.logs": "C:\\Users\\russc\\AppData\\Roaming\\NEST\\6.1.0\\elasticsearch-6.1.0\\logs",
        "path.repo": "C:\\Users\\russc\\AppData\\Roaming\\NEST\\6.1.0\\repositories",
        "script.allowed_types": "inline,stored",
        "script.max_compilations_rate": "10000/1m",
        "search.remote.connect": "true",
        "transport.type.default": "netty4",
        "xpack.notification.hipchat.account.notify-monitoring.profile": "user",
        "xpack.notification.hipchat.account.notify-monitoring.user": "watcher-user@example.com",
        "xpack.security.authc.realms.file1.order": "0",
        "xpack.security.authc.realms.file1.type": "file",
        "xpack.security.authc.realms.pki1.enabled": "false",
        "xpack.security.authc.realms.pki1.order": "1",
        "xpack.security.authc.realms.pki1.type": "pki",
        "xpack.security.enabled": "false",
        "xpack.security.http.ssl.enabled": "false"
      },
      "http": {
        "bound_address": ["127.0.0.1:9200", "[::1]:9200"],
        "publish_address": "127.0.0.1:9200",
        "max_content_length_in_bytes": 104857600
      }
    }
  }
}

Where path.data is returned as an array. This breaks the deserialization of the response, but also does not adhere to the flat_settings parameter.

Steps to reproduce:

Please include a minimal but complete recreation of the problem, including
(e.g.) index creation, mappings, settings, query etc. The easier you make for
us to reproduce it, the more likely that somebody will take the time to look at it.

1. Specify path.data when starting Elasticsearch
2. Execute a request against GET /_nodes/http,settings?flat_settings

[s1monw]

this is caused by #26878 and that is actually a bugfix. The previous behavior was a leak of internal representation and can't be added back. The flat_settings was prone to this problem since it didn't use the actual datatype but the internal representation.

[russcam]

I added #27830 to add this to the 6.1.0 release notes