Reverting to legacy ES client behavior where maxSockets = Infinity (#113644)

* Reverting to legacy ES client behavior where maxSockets = Infinity

* Removing unnused type

* Specifying keepAlive: true by default

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

src/core/server/elasticsearch/client/client_config.test.ts

@@ -37,6 +37,19 @@ describe('parseClientOptions', () => {
     );
   });
 
+  it('specifies `headers.maxSockets` Infinity and `keepAlive` true by default', () => {
+    const config = createConfig({});
+
+    expect(parseClientOptions(config, false)).toEqual(
+      expect.objectContaining({
+        agent: {
+          keepAlive: true,
+          maxSockets: Infinity,
+        },
+      })
+    );
+  });
+
   describe('basic options', () => {
     it('`customHeaders` option', () => {
       const config = createConfig({
@@ -76,11 +89,21 @@ describe('parseClientOptions', () => {
       );
     });
 
-    it('`keepAlive` option', () => {
-      expect(parseClientOptions(createConfig({ keepAlive: true }), false)).toEqual(
-        expect.objectContaining({ agent: { keepAlive: true } })
-      );
-      expect(parseClientOptions(createConfig({ keepAlive: false }), false).agent).toBeUndefined();
+    describe('`keepAlive option`', () => {
+      it('`keepAlive` is true', () => {
+        const options = parseClientOptions(createConfig({ keepAlive: true }), false);
+        expect(options.agent).toHaveProperty('keepAlive', true);
+      });
+
+      it('`keepAlive` is false', () => {
+        const options = parseClientOptions(createConfig({ keepAlive: false }), false);
+        expect(options.agent).toHaveProperty('keepAlive', false);
+      });
+
+      it('`keepAlive` is undefined', () => {
+        const options = parseClientOptions(createConfig({}), false);
+        expect(options.agent).toHaveProperty('keepAlive', true);
+      });
     });
 
     it('`sniffOnStart` options', () => {

src/core/server/elasticsearch/client/client_config.ts

@@ -59,6 +59,10 @@ export function parseClientOptions(
     // do not make assumption on user-supplied data content
     // fixes https://github.com/elastic/kibana/issues/101944
     disablePrototypePoisoningProtection: true,
+    agent: {
+      maxSockets: Infinity,
+      keepAlive: config.keepAlive ?? true,
+    },
   };
 
   if (config.pingTimeout != null) {
@@ -73,11 +77,6 @@ export function parseClientOptions(
         ? config.sniffInterval
         : getDurationAsMs(config.sniffInterval);
   }
-  if (config.keepAlive) {
-    clientOptions.agent = {
-      keepAlive: config.keepAlive,
-    };
-  }
 
   if (!scoped) {
     if (config.username && config.password) {