Add processor architectures to cluster stats

docs/reference/cluster/stats.asciidoc

@@ -766,6 +766,23 @@ Human-readable name of an operating system used by one or more selected nodes.
 Number of selected nodes using the operating system.
 ======
 
+`architectures`::
+(array of objects)
+Contains statistics about processor architectures (for example, x86_64 or
+aarch64) used by selected nodes.
++
+.Properties of `architectures`
+[%collapsible%open]
+======
+`arch`:::
+(string)
+Name of an architecture used by one or more selected nodes.
+
+`count`:::
+(string)
+Number of selected nodes using the architecture.
+======
+
 `mem`::
 (object)
 Contains statistics about memory used by selected nodes.
@@ -1252,6 +1269,12 @@ The API returns the following response:
                "count": 1
             }
          ],
+         "architectures": [
+            {
+               "arch": "x86_64",
+               "count": 1
+            }
+         ],
          "mem" : {
             "total" : "16gb",
             "total_in_bytes" : 17179869184,

server/src/main/java/org/elasticsearch/action/admin/cluster/stats/ClusterStatsNodes.java

@@ -248,6 +248,7 @@ public static class OsStats implements ToXContentFragment {
         final int allocatedProcessors;
         final ObjectIntHashMap<String> names;
         final ObjectIntHashMap<String> prettyNames;
+        final ObjectIntHashMap<String> architectures;
         final org.elasticsearch.monitor.os.OsStats.Mem mem;
 
         /**
@@ -256,6 +257,7 @@ public static class OsStats implements ToXContentFragment {
         private OsStats(List<NodeInfo> nodeInfos, List<NodeStats> nodeStatsList) {
             this.names = new ObjectIntHashMap<>();
             this.prettyNames = new ObjectIntHashMap<>();
+            this.architectures = new ObjectIntHashMap<>();
             int availableProcessors = 0;
             int allocatedProcessors = 0;
             for (NodeInfo nodeInfo : nodeInfos) {
@@ -268,6 +270,9 @@ private OsStats(List<NodeInfo> nodeInfos, List<NodeStats> nodeStatsList) {
                 if (nodeInfo.getInfo(OsInfo.class).getPrettyName() != null) {
                     prettyNames.addTo(nodeInfo.getInfo(OsInfo.class).getPrettyName(), 1);
                 }
+                if (nodeInfo.getInfo(OsInfo.class).getArch() != null) {
+                    architectures.addTo(nodeInfo.getInfo(OsInfo.class).getArch(), 1);
+                }
             }
             this.availableProcessors = availableProcessors;
             this.allocatedProcessors = allocatedProcessors;
@@ -308,6 +313,8 @@ static final class Fields {
             static final String NAMES = "names";
             static final String PRETTY_NAME = "pretty_name";
             static final String PRETTY_NAMES = "pretty_names";
+            static final String ARCH = "arch";
+            static final String ARCHITECTURES = "architectures";
             static final String COUNT = "count";
         }
 
@@ -340,6 +347,18 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params)
                 }
             }
             builder.endArray();
+            builder.startArray(Fields.ARCHITECTURES);
+            {
+                for (final ObjectIntCursor<String> arch : architectures) {
+                    builder.startObject();
+                    {
+                        builder.field(Fields.ARCH, arch.key);
+                        builder.field(Fields.COUNT, arch.value);
+                    }
+                    builder.endObject();
+                }
+            }
+            builder.endArray();
             mem.toXContent(builder, params);
             return builder;
         }

x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java

@@ -269,6 +269,7 @@ public void testToXContent() throws IOException {
         when(mockOsInfo.getAllocatedProcessors()).thenReturn(16);
         when(mockOsInfo.getName()).thenReturn("_os_name");
         when(mockOsInfo.getPrettyName()).thenReturn("_pretty_os_name");
+        when(mockOsInfo.getArch()).thenReturn("_architecture");
 
         final JvmInfo mockJvmInfo = mock(JvmInfo.class);
         when(mockNodeInfo.getInfo(JvmInfo.class)).thenReturn(mockJvmInfo);
@@ -495,6 +496,12 @@ public void testToXContent() throws IOException {
                 + "            \"count\": 1"
                 + "          }"
                 + "        ],"
+                + "        \"architectures\": ["
+                + "          {"
+                + "            \"arch\": \"_architecture\","
+                + "            \"count\": 1"
+                + "          }"
+                + "        ],"
                 + "        \"mem\": {"
                 + "          \"total_in_bytes\": 100,"
                 + "          \"free_in_bytes\": 79,"