🍒 8601 - Introduce cache for peer.hostname lookup (#8611)

* Introduce cache for peer.hostname lookup

(cherry picked from commit 20c6a3d)

* Add switch to turn off peer.hostname collection

(cherry picked from commit 3cf184d)

Author: mcculls

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/decorator/BaseDecorator.java

@@ -6,6 +6,8 @@
 import datadog.trace.api.Config;
 import datadog.trace.api.DDTags;
 import datadog.trace.api.Functions;
+import datadog.trace.api.cache.DDCache;
+import datadog.trace.api.cache.DDCaches;
 import datadog.trace.api.cache.QualifiedClassNameCache;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
@@ -37,6 +39,8 @@ public String apply(Class<?> clazz) {
           },
           Functions.PrefixJoin.of("."));
 
+  private static final DDCache<String, String> HOSTNAME_CACHE = DDCaches.newFixedSizeCache(64);
+
   protected final boolean traceAnalyticsEnabled;
   protected final Double traceAnalyticsSampleRate;
 
@@ -114,13 +118,14 @@ public AgentSpan onPeerConnection(final AgentSpan span, final InetAddress remote
 
   public AgentSpan onPeerConnection(AgentSpan span, InetAddress remoteAddress, boolean resolved) {
     if (remoteAddress != null) {
-      if (resolved) {
-        span.setTag(Tags.PEER_HOSTNAME, remoteAddress.getHostName());
+      String ip = remoteAddress.getHostAddress();
+      if (resolved && Config.get().isPeerHostNameEnabled()) {
+        span.setTag(Tags.PEER_HOSTNAME, hostName(remoteAddress, ip));
       }
       if (remoteAddress instanceof Inet4Address) {
-        span.setTag(Tags.PEER_HOST_IPV4, remoteAddress.getHostAddress());
+        span.setTag(Tags.PEER_HOST_IPV4, ip);
       } else if (remoteAddress instanceof Inet6Address) {
-        span.setTag(Tags.PEER_HOST_IPV6, remoteAddress.getHostAddress());
+        span.setTag(Tags.PEER_HOST_IPV6, ip);
       }
     }
     return span;
@@ -187,4 +192,11 @@ public CharSequence className(final Class<?> clazz) {
     String simpleName = clazz.getSimpleName();
     return simpleName.isEmpty() ? CLASS_NAMES.getClassName(clazz) : simpleName;
   }
+
+  private static String hostName(InetAddress remoteAddress, String ip) {
+    if (null != ip) {
+      return HOSTNAME_CACHE.computeIfAbsent(ip, _ip -> remoteAddress.getHostName());
+    }
+    return remoteAddress.getHostName();
+  }
 }

dd-trace-api/src/main/java/datadog/trace/api/config/TracerConfig.java

@@ -126,12 +126,13 @@ public final class TracerConfig {
       "trace.experimental.long-running.initial.flush.interval";
   public static final String TRACE_LONG_RUNNING_FLUSH_INTERVAL =
       "trace.experimental.long-running.flush.interval";
+
+  public static final String TRACE_PEER_HOSTNAME_ENABLED = "trace.peer.hostname.enabled";
+
   public static final String TRACE_PEER_SERVICE_DEFAULTS_ENABLED =
       "trace.peer.service.defaults.enabled";
-
   public static final String TRACE_PEER_SERVICE_COMPONENT_OVERRIDES =
       "trace.peer.service.component.overrides";
-
   public static final String TRACE_REMOVE_INTEGRATION_SERVICE_NAMES_ENABLED =
       "trace.remove.integration-service-names.enabled";
 

internal-api/src/main/java/datadog/trace/api/Config.java

@@ -146,6 +146,7 @@ public static String getHostName() {
   private final String prioritySamplingForce;
   private final boolean traceResolverEnabled;
   private final int spanAttributeSchemaVersion;
+  private final boolean peerHostNameEnabled;
   private final boolean peerServiceDefaultsEnabled;
   private final Map<String, String> peerServiceComponentOverrides;
   private final boolean removeIntegrationServiceNamesEnabled;
@@ -800,6 +801,8 @@ private Config(final ConfigProvider configProvider, final InstrumenterConfig ins
 
     spanAttributeSchemaVersion = schemaVersionFromConfig();
 
+    peerHostNameEnabled = configProvider.getBoolean(TRACE_PEER_HOSTNAME_ENABLED, true);
+
     // following two only used in v0.
     // in v1+ defaults are always calculated regardless this feature flag
     peerServiceDefaultsEnabled =
@@ -2094,6 +2097,10 @@ public int getSpanAttributeSchemaVersion() {
     return spanAttributeSchemaVersion;
   }
 
+  public boolean isPeerHostNameEnabled() {
+    return peerHostNameEnabled;
+  }
+
   public boolean isPeerServiceDefaultsEnabled() {
     return peerServiceDefaultsEnabled;
   }
@@ -4711,6 +4718,8 @@ public String toString() {
         + jaxRsExceptionAsErrorsEnabled
         + ", axisPromoteResourceName="
         + axisPromoteResourceName
+        + ", peerHostNameEnabled="
+        + peerHostNameEnabled
         + ", peerServiceDefaultsEnabled="
         + peerServiceDefaultsEnabled
         + ", peerServiceComponentOverrides="