[Sampling] add get call for sampling configs

rest-api-spec/src/main/resources/rest-api-spec/api/indices.get_sample_configuration.json

@@ -0,0 +1,38 @@
+{
+  "indices.get_sample_configuration": {
+    "documentation": {
+      "url": "https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-get-sample-configuration",
+      "description": "Get sampling configuration for an index or data stream"
+    },
+    "stability": "experimental",
+    "visibility": "public",
+    "headers": {
+      "accept": [
+        "application/json"
+      ]
+    },
+    "url": {
+      "paths": [
+        {
+          "path": "/{index}/_sample/config",
+          "methods": [
+            "GET"
+          ],
+          "parts": {
+            "index": {
+              "type": "string",
+              "description": "The name of a data stream or index"
+            }
+          }
+        }
+      ]
+    },
+    "params": {
+      "master_timeout": {
+        "type": "time",
+        "description": "Timeout for connection to master node"
+      }
+    }
+  }
+}
+

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_sample_configuration/10_basic.yml

@@ -0,0 +1,179 @@
+---
+setup:
+  - requires:
+      cluster_features: [ "random_sampling" ]
+      reason: requires feature 'random_sampling' to get random samples
+
+---
+teardown:
+  - do:
+      indices.delete:
+        index: "*test*"
+        ignore_unavailable: true
+        allow_no_indices: true
+
+---
+"Get sampling configuration after setting it":
+  - do:
+      indices.create:
+        index: test-get-config-index
+        body:
+          settings:
+            number_of_shards: 1
+
+  - do:
+      indices.put_sample_configuration:
+        index: test-get-config-index
+        body:
+          rate: 0.5
+          max_samples: 100
+          max_size: "10mb"
+          time_to_live: "1h"
+
+  - match: { acknowledged: true }
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-get-config-index
+        human: true
+
+  - match: { configuration.rate: 0.5 }
+  - match: { configuration.max_samples: 100 }
+  - match: { configuration.max_size: "10mb" }
+  - match: { configuration.time_to_live: "1h" }
+
+---
+"Get sampling configuration with minimal parameters":
+  - do:
+      indices.create:
+        index: test-minimal-config-index
+
+  - do:
+      indices.put_sample_configuration:
+        index: test-minimal-config-index
+        body:
+          rate: 0.1
+
+  - match: { acknowledged: true }
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-minimal-config-index
+        human: true
+
+  - match: { configuration.rate: 0.1 }
+
+---
+"Get sampling configuration with condition":
+  - do:
+      indices.create:
+        index: test-condition-config-index
+
+  - do:
+      indices.put_sample_configuration:
+        index: test-condition-config-index
+        body:
+          rate: 1.0
+          max_samples: 50
+          if: "ctx?.field == 'sample_me'"
+
+  - match: { acknowledged: true }
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-condition-config-index
+        human: true
+
+  - match: { configuration.rate: 1.0 }
+  - match: { configuration.max_samples: 50 }
+  - match: { configuration.if: "ctx?.field == 'sample_me'" }
+
+---
+"Get sampling configuration for non-existent index":
+  - do:
+      catch: missing
+      indices.get_sample_configuration:
+        index: non-existent-index
+
+---
+"Get sampling configuration for index without configuration":
+  - do:
+      indices.create:
+        index: test-no-config-index
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-no-config-index
+        human: true
+
+  # Should return empty or default configuration
+  - is_false: test-no-config-index.sampling
+
+---
+"Get sampling configuration after update":
+  - do:
+      indices.create:
+        index: test-update-config-index
+
+  # Set initial configuration
+  - do:
+      indices.put_sample_configuration:
+        index: test-update-config-index
+        body:
+          rate: 0.3
+          max_samples: 25
+
+  - match: { acknowledged: true }
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-update-config-index
+        human: true
+
+  - match: { configuration.rate: 0.3 }
+  - match: { configuration.max_samples: 25 }
+
+  # Update configuration
+  - do:
+      indices.put_sample_configuration:
+        index: test-update-config-index
+        body:
+          rate: 0.8
+          max_samples: 75
+          max_size: "5mb"
+
+  - match: { acknowledged: true }
+
+  # Verify updated configuration
+  - do:
+      indices.get_sample_configuration:
+        index: test-update-config-index
+        human: true
+
+  - match: { configuration.rate: 0.8 }
+  - match: { configuration.max_samples: 75 }
+  - match: { configuration.max_size: "5mb" }
+
+---
+"Get sampling configuration with master timeout":
+  - do:
+      indices.create:
+        index: test-timeout-config-index
+
+  - do:
+      indices.put_sample_configuration:
+        index: test-timeout-config-index
+        body:
+          rate: 0.7
+          max_samples: 200
+
+  - match: { acknowledged: true }
+
+  - do:
+      indices.get_sample_configuration:
+        index: test-timeout-config-index
+        master_timeout: "30s"
+        human: true
+
+  - match: { configuration.rate: 0.7 }
+  - match: { configuration.max_samples: 200 }

server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/sampling/GetSampleConfigurationActionIT.java

@@ -0,0 +1,147 @@
+/*
+ * 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 org.elasticsearch.action.admin.indices.sampling;
+
+import org.elasticsearch.common.unit.ByteSizeValue;
+import org.elasticsearch.core.TimeValue;
+import org.elasticsearch.ingest.SamplingService;
+import org.elasticsearch.test.ESIntegTestCase;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.Matchers.nullValue;
+
+public class GetSampleConfigurationActionIT extends ESIntegTestCase {
+
+    public void testGetSampleConfiguration() {
+        assumeTrue("Requires the sampling feature flag to be enabled", SamplingService.RANDOM_SAMPLING_FEATURE_FLAG);
+
+        String indexName = randomIdentifier();
+        createIndex(indexName);
+
+        // Create a random sampling configuration
+        SamplingConfiguration config = randomSamplingConfiguration();
+        putSamplingConfiguration(indexName, config);
+
+        // Get and verify the sampling configuration
+        assertGetConfigurationMatches(indexName, config);
+    }
+
+    public void testGetSampleConfigurationForNonExistentIndex() {
+        assumeTrue("Requires the sampling feature flag to be enabled", SamplingService.RANDOM_SAMPLING_FEATURE_FLAG);
+
+        String nonExistentIndex = randomIdentifier();
+
+        // Try to get configuration for non-existent index
+        GetSampleConfigurationAction.Request getRequest = new GetSampleConfigurationAction.Request(randomValidTimeValue());
+        getRequest.indices(nonExistentIndex);
+
+        // This should fail - cannot get config for non-existent index
+        expectThrows(Exception.class, () -> client().execute(GetSampleConfigurationAction.INSTANCE, getRequest).actionGet());
+    }
+
+    public void testGetSampleConfigurationForIndexWithoutConfiguration() {
+        assumeTrue("Requires the sampling feature flag to be enabled", SamplingService.RANDOM_SAMPLING_FEATURE_FLAG);
+
+        String indexName = randomIdentifier();
+        createIndex(indexName);
+
+        // Get configuration for index without any sampling configuration
+        GetSampleConfigurationAction.Request getRequest = new GetSampleConfigurationAction.Request(randomValidTimeValue());
+        getRequest.indices(indexName);
+
+        GetSampleConfigurationAction.Response response = client().execute(GetSampleConfigurationAction.INSTANCE, getRequest).actionGet();
+
+        // Verify response returns null configuration
+        assertThat("Response should not be null", response, notNullValue());
+        assertThat("Index name should match", response.getIndex(), equalTo(indexName));
+        assertThat("Configuration should be null for index without config", response.getConfiguration(), nullValue());
+    }
+
+    public void testGetSampleConfigurationAfterUpdate() {
+        assumeTrue("Requires the sampling feature flag to be enabled", SamplingService.RANDOM_SAMPLING_FEATURE_FLAG);
+
+        String indexName = randomIdentifier();
+        createIndex(indexName);
+
+        // Create initial random configuration
+        SamplingConfiguration initialConfig = randomSamplingConfiguration();
+        putSamplingConfiguration(indexName, initialConfig);
+
+        // Get initial configuration
+        assertGetConfigurationMatches(indexName, initialConfig);
+
+        // Update with new random configuration
+        SamplingConfiguration updatedConfig = randomSamplingConfiguration();
+        putSamplingConfiguration(indexName, updatedConfig);
+
+        // Get and verify updated configuration
+        assertGetConfigurationMatches(indexName, updatedConfig);
+    }
+
+    public void testGetSampleConfigurationPersistsAcrossClusterStateUpdates() {
+        assumeTrue("Requires the sampling feature flag to be enabled", SamplingService.RANDOM_SAMPLING_FEATURE_FLAG);
+
+        String indexName = randomIdentifier();
+        createIndex(indexName);
+
+        // Store random sampling configuration
+        SamplingConfiguration config = randomSamplingConfiguration();
+        putSamplingConfiguration(indexName, config);
+
+        // Get initial configuration
+        assertGetConfigurationMatches(indexName, config);
+
+        // Trigger cluster state updates by creating additional indices with random names
+        int numDummyIndices = randomIntBetween(2, 5);
+        for (int i = 0; i < numDummyIndices; i++) {
+            createIndex(randomIdentifier());
+        }
+
+        // Get configuration again after cluster state changes and verify it persists
+        assertGetConfigurationMatches(indexName, config);
+    }
+
+    private SamplingConfiguration randomSamplingConfiguration() {
+        return new SamplingConfiguration(
+            randomDoubleBetween(0.1, 1.0, true),
+            randomBoolean() ? randomIntBetween(1, SamplingConfiguration.MAX_SAMPLES_LIMIT) : null,
+            randomBoolean() ? ByteSizeValue.ofMb(randomIntBetween(1, 100)) : null,
+            randomBoolean() ? randomValidTimeValue() : null,
+            randomBoolean() ? randomAlphaOfLengthBetween(5, 30) : null
+        );
+    }
+
+    private void putSamplingConfiguration(String indexName, SamplingConfiguration config) {
+        PutSampleConfigurationAction.Request putRequest = new PutSampleConfigurationAction.Request(
+            config,
+            randomValidTimeValue(),
+            randomValidTimeValue()
+        );
+        putRequest.indices(indexName);
+        client().execute(PutSampleConfigurationAction.INSTANCE, putRequest).actionGet();
+        ensureGreen();
+    }
+
+    private void assertGetConfigurationMatches(String indexName, SamplingConfiguration expectedConfig) {
+        GetSampleConfigurationAction.Request getRequest = new GetSampleConfigurationAction.Request(randomValidTimeValue());
+        getRequest.indices(indexName);
+
+        GetSampleConfigurationAction.Response response = client().execute(GetSampleConfigurationAction.INSTANCE, getRequest).actionGet();
+
+        assertThat("Response should not be null", response, notNullValue());
+        assertThat("Index name should match", response.getIndex(), equalTo(indexName));
+        assertThat("Configuration should match", response.getConfiguration(), equalTo(expectedConfig));
+    }
+
+    private TimeValue randomValidTimeValue() {
+        return TimeValue.timeValueDays(randomIntBetween(10, 20));
+    }
+}