Get node ID from nodes info in REST tests (#40052)

* Get master identity from nodes info in REST tests

We discussed recently that the cluster state API should be considered
"internal" and therefore our usual cast-iron stability guarantees do not hold
for this API.

However, there are a good number of REST tests that need to identify the master
node. Today they call `GET /_cluster/state` API and extract the master node ID
from the response. An alternative that avoids the unstable cluster state API is
to call `GET _nodes/_master`: the master node ID is the unique key in the
`nodes` map in the response.

This change adds the ability for YAML-based REST tests to extract the unique
key of a singleton map so that they can obtain the master node ID from the
nodes info API instead of the cluster state API.

* Allow access to an arbitrary node ID and adjust all YAML tests to use this

* Warnings

Author: DaveCTurner

rest-api-spec/src/main/resources/rest-api-spec/test/cluster.allocation_explain/10_basic.yml

@@ -12,10 +12,6 @@
 
   - match: { acknowledged: true }
 
-  - do:
-      cluster.state:
-        metric: [ master_node ]
-
   - do:
       cluster.allocation_explain:
         body: { "index": "test", "shard": 0, "primary": true }
@@ -37,10 +33,6 @@
         index: test
         body: { "settings": { "index.number_of_shards": 1, "index.number_of_replicas": 9 } }
 
-  - do:
-      cluster.state:
-        metric: [ master_node ]
-
   - do:
       cluster.allocation_explain:
         include_disk_info: true

rest-api-spec/src/main/resources/rest-api-spec/test/cluster.reroute/11_explain.yml

@@ -25,12 +25,14 @@ setup:
 
 ---
 "Explain API for non-existent node & shard":
+  - skip:
+      features: [arbitrary_key]
 
   - do:
-      cluster.state:
-        metric: [ master_node ]
-
-  - set: {master_node: node_id}
+      nodes.info:
+        node_id: data:true
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       cluster.reroute:

rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml

@@ -3,27 +3,29 @@
   - skip:
       version: " - 6.9.99"
       reason: expects warnings that pre-7.0.0 will not send
-      features: "warnings"
-  # creates an index with one document solely allocated on the master node
+      features: [warnings, arbitrary_key]
+
+  # creates an index with one document solely allocated on a particular data node
   # and shrinks it into a new index with a single shard
   # we don't do the relocation to a single node after the index is created
   # here since in a mixed version cluster we can't identify
   # which node is the one with the highest version and that is the only one that can safely
   # be used to shrink the index.
-  - do:
-      cluster.state: {}
-      # Get master node id
 
-  - set: { master_node: master }
+  - do:
+      nodes.info:
+        node_id: data:true
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       indices.create:
         index: source
         wait_for_active_shards: 1
         body:
           settings:
-            # ensure everything is allocated on a single node
-            index.routing.allocation.include._id: $master
+            # ensure everything is allocated on the same data node
+            index.routing.allocation.include._id: $node_id
             index.number_of_shards: 2
             index.number_of_replicas: 0
   - do:

rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/20_source_mapping.yml

@@ -3,13 +3,13 @@
     - skip:
         version: " - 6.9.99"
         reason: expects warnings that pre-7.0.0 will not send
-        features: "warnings"
+        features: [warnings, arbitrary_key]
 
     - do:
-        cluster.state: {}
-        # Get master node id
-
-    - set: { master_node: master }
+        nodes.info:
+          node_id: data:true
+    - set:
+        nodes._arbitrary_key_: node_id
 
   # create index
     - do:
@@ -19,7 +19,7 @@
           body:
             settings:
               # ensure everything is allocated on a single node
-              index.routing.allocation.include._id: $master
+              index.routing.allocation.include._id: $node_id
               index.number_of_shards: 2
               index.number_of_replicas: 0
             mappings:

rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/30_copy_settings.yml

@@ -3,22 +3,22 @@
   - skip:
       version: " - 6.9.99"
       reason: expects warnings that pre-7.0.0 will not send
-      features: "warnings"
+      features: [warnings, arbitrary_key]
 
   - do:
-      cluster.state: {}
-
-  # get master node id
-  - set: { master_node: master }
+      nodes.info:
+        node_id: data:true
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       indices.create:
         index: source
         wait_for_active_shards: 1
         body:
           settings:
-            # ensure everything is allocated on the master node
-            index.routing.allocation.include._id: $master
+            # ensure everything is allocated on the same node
+            index.routing.allocation.include._id: $node_id
             index.number_of_shards: 2
             index.number_of_replicas: 0
             index.merge.scheduler.max_merge_count: 4
@@ -60,4 +60,4 @@
   - match: { copy-settings-target.settings.index.merge.scheduler.max_merge_count: "4" }
   - match: { copy-settings-target.settings.index.merge.scheduler.max_thread_count: "2" }
   - match: { copy-settings-target.settings.index.blocks.write: "true" }
-  - match: { copy-settings-target.settings.index.routing.allocation.include._id: $master }
+  - match: { copy-settings-target.settings.index.routing.allocation.include._id: $node_id }

rest-api-spec/src/main/resources/rest-api-spec/test/indices.split/30_copy_settings.yml

@@ -3,22 +3,22 @@
   - skip:
       version: " - 6.9.99"
       reason: expects warnings that pre-7.0.0 will not send
-      features: "warnings"
+      features: [arbitrary_key, warnings]
 
   - do:
-      cluster.state: {}
-
-  # get master node id
-  - set: { master_node: master }
+      nodes.info:
+        node_id: data:true
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       indices.create:
         index: source
         wait_for_active_shards: 1
         body:
           settings:
-            # ensure everything is allocated on the master node
-            index.routing.allocation.include._id: $master
+            # ensure everything is allocated on the same node
+            index.routing.allocation.include._id: $node_id
             index.number_of_replicas: 0
             index.number_of_shards: 1
             index.number_of_routing_shards: 4
@@ -62,4 +62,4 @@
   - match: { copy-settings-target.settings.index.merge.scheduler.max_merge_count: "4" }
   - match: { copy-settings-target.settings.index.merge.scheduler.max_thread_count: "2" }
   - match: { copy-settings-target.settings.index.blocks.write: "true" }
-  - match: { copy-settings-target.settings.index.routing.allocation.include._id: $master }
+  - match: { copy-settings-target.settings.index.routing.allocation.include._id: $node_id }

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.info/10_basic.yml

@@ -1,14 +1,13 @@
+setup:
+  - skip:
+      features: [arbitrary_key]
 ---
 "node_info test":
-  - do:
-      cluster.state: {}
-
-  # Get master node id
-  - set: { master_node: master }
-
   - do:
       nodes.info: {}
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - is_true: nodes
   - is_true: cluster_name
-  - is_true: nodes.$master.roles
+  - is_true: nodes.$node_id.roles

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.info/20_transport.yml

@@ -2,15 +2,15 @@
 
 "node_info test profile is empty":
   - skip:
-        features: stash_in_path
+        features: [stash_in_path, arbitrary_key]
 
   - do:
-      cluster.state: {}
-
-  - set: {master_node: master}
+      nodes.info: {}
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       nodes.info:
         metric: [ transport ]
 
-  - is_true: nodes.$master.transport.profiles
+  - is_true: nodes.$node_id.transport.profiles

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.info/30_settings.yml

@@ -1,19 +1,22 @@
 ---
 "node_info test flat_settings":
-  - do:
-      cluster.state: {}
+  - skip:
+      features: [arbitrary_key]
 
-  - set: { master_node: master }
+  - do:
+      nodes.info: {}
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       nodes.info:
         metric: [ settings ]
 
-  - match : { nodes.$master.settings.client.type: node }
+  - match : { nodes.$node_id.settings.client.type: node }
 
   - do:
       nodes.info:
         metric: [ settings ]
         flat_settings: true
 
-  - match : { nodes.$master.settings.client\.type: node }
+  - match : { nodes.$node_id.settings.client\.type: node }

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.stats/10_basic.yml

@@ -9,17 +9,20 @@
 
 ---
 "Nodes stats level":
-  - do:
-      cluster.state: {}
+  - skip:
+      features: [arbitrary_key]
 
-  - set: { master_node: master }
+  - do:
+      nodes.info: {}
+  - set:
+      nodes._arbitrary_key_: node_id
 
   - do:
       nodes.stats:
         metric: [ indices ]
         level: "indices"
 
-  - is_true: nodes.$master.indices.indices
+  - is_true: nodes.$node_id.indices.indices
 
 ---
 "Nodes stats unrecognized parameter":