Improve `randomIdentifier` usage in AWS tests (#125775)

Adds prefixes to various randomly-generated values to make it easier to
pin down where they're coming from in debugging sessions. Also forces
the STS expiry time to be rendered in UTC.

plugins/discovery-ec2/src/javaRestTest/java/org/elasticsearch/discovery/ec2/DiscoveryEc2InstanceProfileIT.java

@@ -10,14 +10,13 @@
 package org.elasticsearch.discovery.ec2;
 
 import fixture.aws.DynamicAwsCredentials;
+import fixture.aws.DynamicRegionSupplier;
 import fixture.aws.ec2.AwsEc2HttpFixture;
 import fixture.aws.imds.Ec2ImdsHttpFixture;
 import fixture.aws.imds.Ec2ImdsServiceBuilder;
 import fixture.aws.imds.Ec2ImdsVersion;
 
-import org.elasticsearch.common.util.LazyInitializable;
 import org.elasticsearch.discovery.DiscoveryModule;
-import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.cluster.ElasticsearchCluster;
 import org.junit.ClassRule;
 import org.junit.rules.RuleChain;
@@ -29,7 +28,7 @@ import java.util.function.Supplier;
 public class DiscoveryEc2InstanceProfileIT extends DiscoveryEc2ClusterFormationTestCase {
 
     // Lazy-initialized so we can generate it randomly, which is not possible in static context.
-    private static final Supplier<String> regionSupplier = new LazyInitializable<>(ESTestCase::randomIdentifier)::getOrCompute;
+    private static final Supplier<String> regionSupplier = new DynamicRegionSupplier();
 
     private static final DynamicAwsCredentials dynamicCredentials = new DynamicAwsCredentials(regionSupplier, "ec2");
 

test/fixtures/aws-fixture-utils/src/main/java/fixture/aws/DynamicRegionSupplier.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package fixture.aws;
+
+import org.elasticsearch.test.ESTestCase;
+
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Supplier;
+
+/**
+ * Lazy supplier for a region name. We cannot use randomness like {@link ESTestCase#randomIdentifier()} when creating the test fixtures in
+ * the first place because this happens in static context, so instead we create one of these and defer the creation of the region name
+ * itself until the test actually starts running.
+ */
+public class DynamicRegionSupplier implements Supplier<String> {
+    private final AtomicReference<String> generatedRegion = new AtomicReference<>();
+
+    @Override
+    public String get() {
+        return Objects.requireNonNullElseGet(generatedRegion.get(), this::generateAndGet);
+    }
+
+    private String generateAndGet() {
+        final var newRegion = "DynamicRegionSupplier-" + ESTestCase.randomIdentifier();
+        return Objects.requireNonNullElse(generatedRegion.compareAndExchange(null, newRegion), newRegion);
+    }
+}

test/fixtures/aws-sts-fixture/src/main/java/fixture/aws/sts/AwsStsHttpHandler.java

@@ -18,6 +18,7 @@ import org.elasticsearch.rest.RestStatus;
 import java.io.IOException;
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
+import java.time.Clock;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
 import java.util.Arrays;
@@ -73,7 +74,7 @@ public class AwsStsHttpHandler implements HttpHandler {
                     exchange.close();
                     return;
                 }
-                final var accessKey = randomIdentifier();
+                final var accessKey = "test_key_STS_" + randomIdentifier();
                 final var sessionToken = randomIdentifier();
                 newCredentialsConsumer.accept(accessKey, sessionToken);
                 final byte[] response = String.format(
@@ -104,7 +105,7 @@ public class AwsStsHttpHandler implements HttpHandler {
                     ROLE_NAME,
                     sessionToken,
                     randomSecretKey(),
-                    ZonedDateTime.now().plusDays(1L).format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssZ")),
+                    ZonedDateTime.now(Clock.systemUTC()).plusDays(1L).format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssZ")),
                     accessKey
                 ).getBytes(StandardCharsets.UTF_8);
                 exchange.getResponseHeaders().add("Content-Type", "text/xml; charset=UTF-8");

test/fixtures/ec2-imds-fixture/src/main/java/fixture/aws/imds/Ec2ImdsHttpHandler.java

@@ -121,7 +121,7 @@ public class Ec2ImdsHttpHandler implements HttpHandler {
 
             if ("GET".equals(requestMethod)) {
                 if (path.equals(IMDS_SECURITY_CREDENTIALS_PATH) && dynamicProfileNames) {
-                    final var profileName = randomIdentifier();
+                    final var profileName = "imds_profile_" + randomIdentifier();
                     validCredentialsEndpoints.add(IMDS_SECURITY_CREDENTIALS_PATH + profileName);
                     sendStringResponse(exchange, profileName);
                     return;
@@ -133,7 +133,7 @@ public class Ec2ImdsHttpHandler implements HttpHandler {
                     sendStringResponse(exchange, Strings.toString(instanceIdentityDocument));
                     return;
                 } else if (validCredentialsEndpoints.contains(path)) {
-                    final String accessKey = randomIdentifier();
+                    final String accessKey = "test_key_imds_" + randomIdentifier();
                     final String sessionToken = randomIdentifier();
                     newCredentialsConsumer.accept(accessKey, sessionToken);
                     final byte[] response = Strings.format(