Make client.name low cardinality keyvalue for client observations

Prior to this commit, the `"client.name"` key value for the
`"http.client.requests"` client HTTP observations would be considered as
high cardinality, as the URI host is technically unbounded.
In practice, the number of hosts used by a client in a given application
can be considered as low cardinality. This commit moves this keyvalue to
low cardinality so that it's present for both metrics and traces.

Closes gh-29839

framework-docs/src/docs/asciidoc/integration/observability.adoc

@@ -131,18 +131,18 @@ Instrumentation is using the `org.springframework.http.client.observation.Client
 [cols="a,a"]
 |===
 |Name | Description
-|`exception` _(required)_|Name of the exception thrown during the exchange, or `"none"` if no exception happened.
 |`method` _(required)_|Name of HTTP request method or `"none"` if the request could not be created.
-|`outcome` _(required)_|Outcome of the HTTP client exchange.
-|`status` _(required)_|HTTP response raw status code, or `"IO_ERROR"` in case of `IOException`, or `"CLIENT_ERROR"` if no response was received.
 |`uri` _(required)_|URI template used for HTTP request, or `"none"` if none was provided.
+|`client.name` _(required)_|Client name derived from the request URI host.
+|`status` _(required)_|HTTP response raw status code, or `"IO_ERROR"` in case of `IOException`, or `"CLIENT_ERROR"` if no response was received.
+|`outcome` _(required)_|Outcome of the HTTP client exchange.
+|`exception` _(required)_|Name of the exception thrown during the exchange, or `"none"` if no exception happened.
 |===
 
 .High cardinality Keys
 [cols="a,a"]
 |===
 |Name | Description
-|`client.name` _(required)_|Client name derived from the request URI host.
 |`http.url` _(required)_|HTTP request URI.
 |===
 
@@ -157,18 +157,18 @@ Instrumentation is using the `org.springframework.web.reactive.function.client.C
 [cols="a,a"]
 |===
 |Name | Description
-|`exception` _(required)_|Name of the exception thrown during the exchange, or `"none"` if no exception happened.
 |`method` _(required)_|Name of HTTP request method or `"none"` if the request could not be created.
-|`outcome` _(required)_|Outcome of the HTTP client exchange.
-|`status` _(required)_|HTTP response raw status code, or `"IO_ERROR"` in case of `IOException`, or `"CLIENT_ERROR"` if no response was received.
 |`uri` _(required)_|URI template used for HTTP request, or `"none"` if none was provided.
+|`client.name` _(required)_|Client name derived from the request URI host.
+|`status` _(required)_|HTTP response raw status code, or `"IO_ERROR"` in case of `IOException`, or `"CLIENT_ERROR"` if no response was received.
+|`outcome` _(required)_|Outcome of the HTTP client exchange.
+|`exception` _(required)_|Name of the exception thrown during the exchange, or `"none"` if no exception happened.
 |===
 
 .High cardinality Keys
 [cols="a,a"]
 |===
 |Name | Description
-|`client.name` _(required)_|Client name derived from the request URI host.
 |`http.url` _(required)_|HTTP request URI.
 |===
 

spring-web/src/main/java/org/springframework/http/client/observation/ClientHttpObservationDocumentation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,7 +50,7 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 
 		@Override
 		public KeyName[] getHighCardinalityKeyNames() {
-			return HighCardinalityKeyNames.values();
+			return new KeyName[] {HighCardinalityKeyNames.HTTP_URL};
 		}
 
 	};
@@ -89,6 +89,17 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 			}
 		},
 
+
+		/**
+		 * Client name derived from the request URI host.
+		 */
+		CLIENT_NAME {
+			@Override
+			public String asString() {
+				return "client.name";
+			}
+		},
+
 		/**
 		 * Name of the exception thrown during the exchange, or {@value KeyValue#NONE_VALUE} if no exception happened.
 		 */
@@ -126,7 +137,10 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 
 		/**
 		 * Client name derived from the request URI host.
+		 * @deprecated in favor of {@link LowCardinalityKeyNames#CLIENT_NAME}.
+		 * This will be available both as a low and high cardinality key value.
 		 */
+		@Deprecated(since = "6.0.5", forRemoval = true)
 		CLIENT_NAME {
 			@Override
 			public String asString() {

spring-web/src/main/java/org/springframework/http/client/observation/DefaultClientRequestObservationConvention.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,12 +51,12 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	private static final KeyValue HTTP_OUTCOME_UNKNOWN = KeyValue.of(LowCardinalityKeyNames.OUTCOME, "UNKNOWN");
 
+	private static final KeyValue CLIENT_NAME_NONE = KeyValue.of(LowCardinalityKeyNames.CLIENT_NAME, KeyValue.NONE_VALUE);
+
 	private static final KeyValue EXCEPTION_NONE = KeyValue.of(LowCardinalityKeyNames.EXCEPTION, KeyValue.NONE_VALUE);
 
 	private static final KeyValue HTTP_URL_NONE = KeyValue.of(HighCardinalityKeyNames.HTTP_URL, KeyValue.NONE_VALUE);
 
-	private static final KeyValue CLIENT_NAME_NONE = KeyValue.of(HighCardinalityKeyNames.CLIENT_NAME, KeyValue.NONE_VALUE);
-
 
 	private final String name;
 
@@ -87,7 +87,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	@Override
 	public KeyValues getLowCardinalityKeyValues(ClientRequestObservationContext context) {
-		return KeyValues.of(uri(context), method(context), status(context), exception(context), outcome(context));
+		return KeyValues.of(uri(context), method(context), status(context), clientName(context), exception(context), outcome(context));
 	}
 
 	protected KeyValue uri(ClientRequestObservationContext context) {
@@ -119,6 +119,13 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 		}
 	}
 
+	protected KeyValue clientName(ClientRequestObservationContext context) {
+		if (context.getCarrier() != null && context.getCarrier().getURI().getHost() != null) {
+			return KeyValue.of(LowCardinalityKeyNames.CLIENT_NAME, context.getCarrier().getURI().getHost());
+		}
+		return CLIENT_NAME_NONE;
+	}
+
 	protected KeyValue exception(ClientRequestObservationContext context) {
 		Throwable error = context.getError();
 		if (error != null) {
@@ -129,7 +136,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 		return EXCEPTION_NONE;
 	}
 
-	protected static KeyValue outcome(ClientRequestObservationContext context) {
+	protected KeyValue outcome(ClientRequestObservationContext context) {
 		if (context.getResponse() != null) {
 			try {
 				return HttpOutcome.forStatus(context.getResponse().getStatusCode());
@@ -143,7 +150,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	@Override
 	public KeyValues getHighCardinalityKeyValues(ClientRequestObservationContext context) {
-		return KeyValues.of(requestUri(context), clientName(context));
+		return KeyValues.of(requestUri(context));
 	}
 
 	protected KeyValue requestUri(ClientRequestObservationContext context) {
@@ -153,12 +160,6 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 		return HTTP_URL_NONE;
 	}
 
-	protected KeyValue clientName(ClientRequestObservationContext context) {
-		if (context.getCarrier() != null && context.getCarrier().getURI().getHost() != null) {
-			return KeyValue.of(HighCardinalityKeyNames.CLIENT_NAME, context.getCarrier().getURI().getHost());
-		}
-		return CLIENT_NAME_NONE;
-	}
 
 	static class HttpOutcome {
 

spring-web/src/test/java/org/springframework/http/client/observation/DefaultClientRequestObservationConventionTests.java

@@ -69,9 +69,8 @@ class DefaultClientRequestObservationConventionTests {
 		context.setUriTemplate("/resource/{id}");
 		assertThat(this.observationConvention.getLowCardinalityKeyValues(context))
 				.contains(KeyValue.of("exception", "none"), KeyValue.of("method", "GET"), KeyValue.of("uri", "/resource/{id}"),
-						KeyValue.of("status", "200"), KeyValue.of("outcome", "SUCCESS"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2)
-				.contains(KeyValue.of("client.name", "none"), KeyValue.of("http.url", "/resource/42"));
+						KeyValue.of("status", "200"), KeyValue.of("client.name", "none"), KeyValue.of("outcome", "SUCCESS"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).contains(KeyValue.of("http.url", "/resource/42"));
 	}
 
 	@Test
@@ -79,9 +78,8 @@ class DefaultClientRequestObservationConventionTests {
 		ClientRequestObservationContext context = createContext(
 				new MockClientHttpRequest(HttpMethod.GET, "/resource/42"), new MockClientHttpResponse());
 		assertThat(this.observationConvention.getLowCardinalityKeyValues(context))
-				.contains(KeyValue.of("method", "GET"), KeyValue.of("uri", "none"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2)
-				.contains(KeyValue.of("http.url", "/resource/42"));
+				.contains(KeyValue.of("method", "GET"), KeyValue.of("client.name", "none"), KeyValue.of("uri", "none"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).contains(KeyValue.of("http.url", "/resource/42"));
 	}
 
 	@Test
@@ -89,7 +87,7 @@ class DefaultClientRequestObservationConventionTests {
 		ClientRequestObservationContext context = createContext(
 				new MockClientHttpRequest(HttpMethod.GET, "https://localhost:8080/resource/42"),
 				new MockClientHttpResponse());
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).contains(KeyValue.of("client.name", "localhost"));
+		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).contains(KeyValue.of("client.name", "localhost"));
 	}
 
 	@Test

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/ClientHttpObservationDocumentation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,7 +47,7 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 
 		@Override
 		public KeyName[] getHighCardinalityKeyNames() {
-			return HighCardinalityKeyNames.values();
+			return new KeyName[] {HighCardinalityKeyNames.HTTP_URL};
 		}
 
 	};
@@ -86,6 +86,16 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 			}
 		},
 
+		/**
+		 * Client name derived from the request URI host.
+		 */
+		CLIENT_NAME {
+			@Override
+			public String asString() {
+				return "client.name";
+			}
+		},
+
 		/**
 		 * Name of the exception thrown during the exchange, or {@value KeyValue#NONE_VALUE} if no exception happened.
 		 */
@@ -124,7 +134,10 @@ public enum ClientHttpObservationDocumentation implements ObservationDocumentati
 
 		/**
 		 * Client name derived from the request URI host.
+		 * @deprecated in favor of {@link LowCardinalityKeyNames#CLIENT_NAME}.
+		 * This will be available both as a low and high cardinality key value.
 		 */
+		@Deprecated(since = "6.0.5", forRemoval = true)
 		CLIENT_NAME {
 			@Override
 			public String asString() {

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientRequestObservationConvention.java

@@ -50,11 +50,12 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	private static final KeyValue HTTP_OUTCOME_UNKNOWN = KeyValue.of(LowCardinalityKeyNames.OUTCOME, "UNKNOWN");
 
+	private static final KeyValue CLIENT_NAME_NONE = KeyValue.of(LowCardinalityKeyNames.CLIENT_NAME, KeyValue.NONE_VALUE);
+
 	private static final KeyValue EXCEPTION_NONE = KeyValue.of(LowCardinalityKeyNames.EXCEPTION, KeyValue.NONE_VALUE);
 
 	private static final KeyValue HTTP_URL_NONE = KeyValue.of(HighCardinalityKeyNames.HTTP_URL, KeyValue.NONE_VALUE);
 
-	private static final KeyValue CLIENT_NAME_NONE = KeyValue.of(HighCardinalityKeyNames.CLIENT_NAME, KeyValue.NONE_VALUE);
 
 	private final String name;
 
@@ -86,7 +87,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	@Override
 	public KeyValues getLowCardinalityKeyValues(ClientRequestObservationContext context) {
-		return KeyValues.of(uri(context), method(context), status(context), exception(context), outcome(context));
+		return KeyValues.of(uri(context), method(context), status(context), clientName(context), exception(context), outcome(context));
 	}
 
 	protected KeyValue uri(ClientRequestObservationContext context) {
@@ -119,6 +120,13 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 		return STATUS_CLIENT_ERROR;
 	}
 
+	protected KeyValue clientName(ClientRequestObservationContext context) {
+		if (context.getRequest() != null && context.getRequest().url().getHost() != null) {
+			return KeyValue.of(LowCardinalityKeyNames.CLIENT_NAME, context.getRequest().url().getHost());
+		}
+		return CLIENT_NAME_NONE;
+	}
+
 	protected KeyValue exception(ClientRequestObservationContext context) {
 		Throwable error = context.getError();
 		if (error != null) {
@@ -141,7 +149,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 
 	@Override
 	public KeyValues getHighCardinalityKeyValues(ClientRequestObservationContext context) {
-		return KeyValues.of(httpUrl(context), clientName(context));
+		return KeyValues.of(httpUrl(context));
 	}
 
 	protected KeyValue httpUrl(ClientRequestObservationContext context) {
@@ -151,13 +159,6 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 		return HTTP_URL_NONE;
 	}
 
-	protected KeyValue clientName(ClientRequestObservationContext context) {
-		if (context.getRequest() != null && context.getRequest().url().getHost() != null) {
-			return KeyValue.of(HighCardinalityKeyNames.CLIENT_NAME, context.getRequest().url().getHost());
-		}
-		return CLIENT_NAME_NONE;
-	}
-
 	static class HttpOutcome {
 
 		static KeyValue forStatus(HttpStatusCode statusCode) {

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/DefaultClientRequestObservationConventionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -58,22 +58,23 @@ class DefaultClientRequestObservationConventionTests {
 	@Test
 	void shouldAddKeyValuesForNullExchange() {
 		ClientRequestObservationContext context = new ClientRequestObservationContext();
-		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).hasSize(5)
+		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).hasSize(6)
 				.contains(KeyValue.of("method", "none"), KeyValue.of("uri", "none"), KeyValue.of("status", "CLIENT_ERROR"),
+						KeyValue.of("client.name", "none"),
 						KeyValue.of("exception", "none"), KeyValue.of("outcome", "UNKNOWN"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2)
-				.contains(KeyValue.of("client.name", "none"), KeyValue.of("http.url", "none"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(1)
+				.contains(KeyValue.of("http.url", "none"));
 	}
 
 	@Test
 	void shouldAddKeyValuesForExchangeWithException() {
 		ClientRequestObservationContext context = new ClientRequestObservationContext();
 		context.setError(new IllegalStateException("Could not create client request"));
-		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).hasSize(5)
+		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).hasSize(6)
 				.contains(KeyValue.of("method", "none"), KeyValue.of("uri", "none"), KeyValue.of("status", "CLIENT_ERROR"),
-						KeyValue.of("exception", "IllegalStateException"), KeyValue.of("outcome", "UNKNOWN"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2)
-				.contains(KeyValue.of("client.name", "none"), KeyValue.of("http.url", "none"));
+						KeyValue.of("client.name", "none"), KeyValue.of("exception", "IllegalStateException"), KeyValue.of("outcome", "UNKNOWN"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(1)
+				.contains(KeyValue.of("http.url", "none"));
 	}
 
 	@Test
@@ -85,9 +86,9 @@ class DefaultClientRequestObservationConventionTests {
 		context.setRequest(context.getCarrier().build());
 		assertThat(this.observationConvention.getLowCardinalityKeyValues(context))
 				.contains(KeyValue.of("exception", "none"), KeyValue.of("method", "GET"), KeyValue.of("uri", "/resource/{id}"),
-						KeyValue.of("status", "200"), KeyValue.of("outcome", "SUCCESS"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2)
-				.contains(KeyValue.of("client.name", "none"), KeyValue.of("http.url", "/resource/42"));
+						KeyValue.of("status", "200"), KeyValue.of("client.name", "none"), KeyValue.of("outcome", "SUCCESS"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(1)
+				.contains(KeyValue.of("http.url", "/resource/42"));
 	}
 
 	@Test
@@ -96,14 +97,14 @@ class DefaultClientRequestObservationConventionTests {
 		context.setRequest(context.getCarrier().build());
 		assertThat(this.observationConvention.getLowCardinalityKeyValues(context))
 				.contains(KeyValue.of("method", "GET"), KeyValue.of("uri", "none"));
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(2).contains(KeyValue.of("http.url", "/resource/42"));
+		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).hasSize(1).contains(KeyValue.of("http.url", "/resource/42"));
 	}
 
 	@Test
 	void shouldAddClientNameKeyValueForRequestWithHost() {
 		ClientRequestObservationContext context = createContext(ClientRequest.create(HttpMethod.GET, URI.create("https://localhost:8080/resource/42")));
 		context.setRequest(context.getCarrier().build());
-		assertThat(this.observationConvention.getHighCardinalityKeyValues(context)).contains(KeyValue.of("client.name", "localhost"));
+		assertThat(this.observationConvention.getLowCardinalityKeyValues(context)).contains(KeyValue.of("client.name", "localhost"));
 	}
 
 	private ClientRequestObservationContext createContext(ClientRequest.Builder request) {