[Backport 8.18] Put node roles support back

docs/basic-config.asciidoc

@@ -171,7 +171,18 @@ a|`function` - Takes a `Connection` and returns `true` if it can be sent a reque
 _Default:_
 [source,js]
 ----
-() => true
+function defaultNodeFilter (conn) {
+  if (conn.roles != null) {
+    if (
+      // avoid master-only nodes
+      conn.roles.master &&
+      !conn.roles.data &&
+      !conn.roles.ingest &&
+      !conn.roles.ml
+    ) return false
+  }
+  return true
+}
 ----
 
 |`nodeSelector`

src/client.ts

@@ -78,6 +78,13 @@ export interface NodeOptions {
   ssl?: TlsConnectionOptions
   /** @property headers Custom HTTP headers that should be sent with each request */
   headers?: Record<string, any>
+  /** @property roles Common Elasticsearch roles that can be assigned to this node. Can be helpful when writing custom nodeFilter or nodeSelector functions. */
+  roles?: {
+    master: boolean
+    data: boolean
+    ingest: boolean
+    ml: boolean
+  }
 }
 
 export interface ClientOptions {
@@ -135,7 +142,7 @@ export interface ClientOptions {
     * @defaultValue null */
   agent?: HttpAgentOptions | UndiciAgentOptions | agentFn | false
   /** @property nodeFilter A custom function used by the connection pool to determine which nodes are qualified to receive a request
-    * @defaultValue () => true */
+    * @defaultValue A function that uses the Connection `roles` property to avoid master-only nodes */
   nodeFilter?: nodeFilterFn
   /** @property nodeSelector A custom function used by the connection pool to determine which node should receive the next request
     * @defaultValue A "round robin" function that loops sequentially through each node in the pool. */

test/unit/client.test.ts

@@ -77,6 +77,31 @@ test('Missing node(s)', t => {
   t.end()
 })
 
+test('multi nodes with roles, using default node filter', async t => {
+  const client = new Client({
+    nodes: [
+      {
+        url: new URL('http://node1:9200'),
+        roles: { master: true, data: false, ingest: false, ml: false }
+      },
+      {
+        url: new URL('http://node2:9200'),
+        roles: { master: true, data: true, ingest: false, ml: false }
+      },
+    ]
+  })
+  const conn = client.connectionPool.getConnection({
+    now: Date.now() + 1000 * 60 * 3,
+    requestId: 1,
+    name: 'elasticsearch-js',
+    context: null
+  })
+
+  t.equal(conn?.url.hostname, 'node2')
+
+  t.end()
+})
+
 test('Custom headers', t => {
   const client = new Client({
     node: 'http://localhost:9200',