add more specific metrics and logging for DNS lookup failures

dialogue-clients/metrics.md

@@ -68,6 +68,8 @@ Dialogue DNS metrics.
     - `success`: DNS resolution succeeded using `InetAddress.getAllByName`.
     - `fallback`: DNS resolution using the primary mechanism failed, however addresses were available in the fallback cache.
     - `failure`: No addresses could be resolved for the given hostname.
+- `client.dns.lookupError` (meter): DNS resolver query failures.
+  - `error-type`: Describes the error type returned by getaddrinfo() when lookup fails.
 
 ### client.uri
 Dialogue URI parsing metrics.

dialogue-clients/src/main/java/com/palantir/dialogue/clients/DefaultDialogueDnsResolver.java

@@ -19,17 +19,25 @@
 import com.google.common.collect.ImmutableSet;
 import com.palantir.dialogue.core.DialogueDnsResolver;
 import com.palantir.logsafe.Preconditions;
+import com.palantir.logsafe.Safe;
+import com.palantir.logsafe.SafeArg;
 import com.palantir.logsafe.UnsafeArg;
 import com.palantir.logsafe.logger.SafeLogger;
 import com.palantir.logsafe.logger.SafeLoggerFactory;
+import com.palantir.tritium.metrics.registry.TaggedMetricRegistry;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.util.Optional;
 
-enum DefaultDialogueDnsResolver implements DialogueDnsResolver {
-    INSTANCE;
-
+final class DefaultDialogueDnsResolver implements DialogueDnsResolver {
     private static final SafeLogger log = SafeLoggerFactory.get(DefaultDialogueDnsResolver.class);
 
+    private final ClientDnsMetrics metrics;
+
+    DefaultDialogueDnsResolver(TaggedMetricRegistry registry) {
+        this.metrics = ClientDnsMetrics.of(registry);
+    }
+
     @Override
     public ImmutableSet<InetAddress> resolve(String hostname) {
         Preconditions.checkNotNull(hostname, "hostname is required");
@@ -41,8 +49,81 @@ public ImmutableSet<InetAddress> resolve(String hostname) {
             }
             return ImmutableSet.copyOf(results);
         } catch (UnknownHostException e) {
-            log.warn("Unknown host '{}'", UnsafeArg.of("hostname", hostname), e);
+            GaiError gaiError = extractGaiErrorString(e);
+            log.warn(
+                    "Unknown host '{}'",
+                    SafeArg.of("gaiErrorType", gaiError.name()),
+                    SafeArg.of("gaiErrorMessage", gaiError.errorMessage()),
+                    UnsafeArg.of("hostname", hostname),
+                    e);
+            metrics.lookupError(gaiError.name()).mark();
             return ImmutableSet.of();
         }
     }
+
+    // these strings were taken from glibc-2.39, but likely have not changed in quite a while
+    // strings may be different on BSD systems like macos
+    // TODO(dns): update this list to try to match against known strings on other platforms
+    private enum GaiError {
+        EAI_ADDRFAMILY("Address family for hostname not supported"),
+        EAI_AGAIN("Temporary failure in name resolution"),
+        EAI_BADFLAGS("Bad value for ai_flags"),
+        EAI_FAIL("Non-recoverable failure in name resolution"),
+        EAI_FAMILY("ai_family not supported"),
+        EAI_MEMORY("Memory allocation failure"),
+        EAI_NODATA("No address associated with hostname"),
+        EAI_NONAME("Name or service not known"),
+        EAI_SERVICE("Servname not supported for ai_socktype"),
+        EAI_SOCKTYPE("ai_socktype not supported"),
+        EAI_SYSTEM("System error"),
+        EAI_INPROGRESS("Processing request in progress"),
+        EAI_CANCELED("Request canceled"),
+        EAI_NOTCANCELED("Request not canceled"),
+        EAI_ALLDONE("All requests done"),
+        EAI_INTR("Interrupted by a signal"),
+        EAI_IDN_ENCODE("Parameter string not correctly encoded"),
+        EAI_OVERFLOW("Result too large for supplied buffer"),
+        CACHED(),
+        UNKNOWN();
+
+        private final Optional<String> errorMessage;
+
+        GaiError() {
+            this.errorMessage = Optional.empty();
+        }
+
+        GaiError(String errorMessage) {
+            this.errorMessage = Optional.of(errorMessage);
+        }
+
+        @Safe
+        String errorMessage() {
+            return errorMessage.orElseGet(this::name);
+        }
+    }
+
+    private static GaiError extractGaiErrorString(UnknownHostException exception) {
+        if (exception.getMessage() == null) {
+            return GaiError.UNKNOWN;
+        }
+
+        try {
+            StackTraceElement[] trace = exception.getStackTrace();
+            if (trace.length > 0) {
+                StackTraceElement top = trace[0];
+                if ("java.net.InetAddress$CachedLookup".equals(top.getClassName())) {
+                    return GaiError.CACHED;
+                }
+
+                for (GaiError error : GaiError.values()) {
+                    if (error.errorMessage.isPresent() && exception.getMessage().contains(error.errorMessage.get())) {
+                        return error;
+                    }
+                }
+            }
+            return GaiError.UNKNOWN;
+        } catch (Exception e) {
+            return GaiError.UNKNOWN;
+        }
+    }
 }

dialogue-clients/src/main/metrics/dialogue-core-metrics.yml

@@ -37,3 +37,9 @@ namespaces:
               - value: failure
                 docs: No addresses could be resolved for the given hostname.
         docs: DNS resolver query metrics, on a per-hostname basis.
+      lookupError:
+        type: meter
+        tags: 
+          - name: error-type
+            docs: Describes the error type returned by getaddrinfo() when lookup fails.
+        docs: DNS resolver query failures.

dialogue-clients/src/test/java/com/palantir/dialogue/clients/DefaultDialogueDnsResolverTest.java

@@ -18,9 +18,13 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assumptions.assumeThat;
 
 import com.google.common.collect.ImmutableSet;
+import com.palantir.dialogue.core.DialogueDnsResolver;
 import com.palantir.logsafe.exceptions.SafeNullPointerException;
+import com.palantir.tritium.metrics.registry.DefaultTaggedMetricRegistry;
+import com.palantir.tritium.metrics.registry.TaggedMetricRegistry;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import org.junit.jupiter.api.Test;
@@ -66,7 +70,42 @@ void malformedIpv6_noBrackets() {
         assertThat(resolve("::z")).isEmpty();
     }
 
+    @Test
+    void unknown_host() {
+        assumeThat(System.getProperty("os.name").toLowerCase().startsWith("linux"))
+                .describedAs("GAI Error Strings are only defined for Linux environments")
+                .isTrue();
+
+        TaggedMetricRegistry registry = new DefaultTaggedMetricRegistry();
+        DialogueDnsResolver resolver = new DefaultDialogueDnsResolver(registry);
+
+        String badHost = "alksdjflajsdlkfjalksjflkadjsf.com";
+        ImmutableSet<InetAddress> result = resolver.resolve(badHost);
+
+        assertThat(result).isEmpty();
+        ClientDnsMetrics metrics = ClientDnsMetrics.of(registry);
+        assertThat(metrics.lookupError("EAI_NONAME").getCount()).isGreaterThan(0);
+    }
+
+    @Test
+    void unknown_host_from_cache() {
+        TaggedMetricRegistry registry = new DefaultTaggedMetricRegistry();
+        DialogueDnsResolver resolver = new DefaultDialogueDnsResolver(registry);
+
+        String badHost = "alksdjflajsdlkfjalksjflkadjsf.com";
+        ImmutableSet<InetAddress> result = resolver.resolve(badHost);
+
+        assertThat(result).isEmpty();
+
+        // should resolve from cache
+        ImmutableSet<InetAddress> result2 = resolver.resolve(badHost);
+        assertThat(result2).isEmpty();
+        ClientDnsMetrics metrics = ClientDnsMetrics.of(registry);
+        assertThat(metrics.lookupError("CACHED").getCount()).isGreaterThan(0);
+    }
+
     private static ImmutableSet<InetAddress> resolve(String hostname) {
-        return DefaultDialogueDnsResolver.INSTANCE.resolve(hostname);
+        DialogueDnsResolver resolver = new DefaultDialogueDnsResolver(new DefaultTaggedMetricRegistry());
+        return resolver.resolve(hostname);
     }
 }