[Default Configuration Part 2]:Implement auto mode discovery

core/aws-core/src/main/java/software/amazon/awssdk/awscore/internal/defaultsmode/AutoDefaultsModeDiscovery.java

@@ -27,11 +27,12 @@
 import software.amazon.awssdk.utils.internal.SystemSettingUtils;
 
 /**
- * This class attempts to discover the appropriate {@link DefaultsMode} the mode by inspecting the environment. It falls
- * back to the standard defaults mode if the target mode cannot be determined.
+ * This class attempts to discover the appropriate {@link DefaultsMode} by inspecting the environment. It falls
+ * back to the {@link DefaultsMode#STANDARD} mode if the target mode cannot be determined.
  */
 @SdkInternalApi
 public final class AutoDefaultsModeDiscovery {
+    private static final String EC2_METADATA_REGION_PATH = "/latest/meta-data/placement/region";
     private static final DefaultsMode FALLBACK_DEFAULTS_MODE = DefaultsMode.STANDARD;
     private static final String ANDROID_JAVA_VENDOR = "The Android Project";
     private static final String AWS_DEFAULT_REGION_ENV_VAR = "AWS_DEFAULT_REGION";
@@ -54,20 +55,20 @@ public DefaultsMode discover(Region regionResolvedFromSdkClient) {
             Optional<String> regionStr = regionFromAwsExecutionEnvironment();
 
             if (regionStr.isPresent()) {
-                return compareRegion(regionStr.get(), regionResolvedFromSdkClient.id());
+                return compareRegion(regionStr.get(), regionResolvedFromSdkClient);
             }
         }
 
         Optional<String> regionFromEc2 = queryImdsV2();
         if (regionFromEc2.isPresent()) {
-            return compareRegion(regionFromEc2.get(), regionResolvedFromSdkClient.id());
+            return compareRegion(regionFromEc2.get(), regionResolvedFromSdkClient);
         }
 
         return FALLBACK_DEFAULTS_MODE;
     }
 
-    private static DefaultsMode compareRegion(String region, String anotherRegion) {
-        if (region.equalsIgnoreCase(anotherRegion)) {
+    private static DefaultsMode compareRegion(String region, Region clientRegion) {
+        if (region.equalsIgnoreCase(clientRegion.id())) {
             return DefaultsMode.IN_REGION;
         }
 
@@ -76,7 +77,7 @@ private static DefaultsMode compareRegion(String region, String anotherRegion) {
 
     private static Optional<String> queryImdsV2() {
         try {
-            String ec2InstanceRegion = EC2MetadataUtils.getEC2InstanceRegion();
+            String ec2InstanceRegion = EC2MetadataUtils.fetchData(EC2_METADATA_REGION_PATH, false, 1);
             // ec2InstanceRegion could be null
             return Optional.ofNullable(ec2InstanceRegion);
         } catch (Exception exception) {

core/aws-core/src/test/java/software/amazon/awssdk/awscore/internal/AutoDefaultsModeDiscoveryTest.java

@@ -35,6 +35,7 @@
 import software.amazon.awssdk.core.SdkSystemSetting;
 import software.amazon.awssdk.defaultsmode.DefaultsMode;
 import software.amazon.awssdk.regions.Region;
+import software.amazon.awssdk.regions.internal.util.EC2MetadataUtils;
 import software.amazon.awssdk.testutils.EnvironmentVariableHelper;
 import software.amazon.awssdk.utils.JavaSystemSetting;
 
@@ -47,35 +48,50 @@ public class AutoDefaultsModeDiscoveryTest {
     @Parameterized.Parameters
     public static Collection<Object> data() {
         return Arrays.asList(new Object[] {
+
+            // Mobile
             new TestData().clientRegion(Region.US_EAST_1)
                           .javaVendorProperty("The Android Project")
                           .awsExecutionEnvVar("AWS_Lambda_java8")
                           .awsRegionEnvVar("us-east-1")
                 .expectedResolvedMode(DefaultsMode.MOBILE),
 
+            // Region available from AWS execution environment
             new TestData().clientRegion(Region.US_EAST_1)
                           .awsExecutionEnvVar("AWS_Lambda_java8")
                           .awsRegionEnvVar("us-east-1")
                 .expectedResolvedMode(DefaultsMode.IN_REGION),
 
+            // Region available from AWS execution environment
             new TestData().clientRegion(Region.US_EAST_1)
                           .awsExecutionEnvVar("AWS_Lambda_java8")
                           .awsDefaultRegionEnvVar("us-west-2")
                 .expectedResolvedMode(DefaultsMode.CROSS_REGION),
 
+            // ImdsV2 available, in-region
             new TestData().clientRegion(Region.US_EAST_1)
                           .awsDefaultRegionEnvVar("us-west-2")
                           .ec2MetadataConfig(new Ec2MetadataConfig().region("us-east-1")
                                                                     .imdsAvailable(true))
                 .expectedResolvedMode(DefaultsMode.IN_REGION),
 
+            // ImdsV2 available, cross-region
             new TestData().clientRegion(Region.US_EAST_1)
                           .awsDefaultRegionEnvVar("us-west-2")
                           .ec2MetadataConfig(new Ec2MetadataConfig().region("us-west-2")
                                                                     .imdsAvailable(true)
                                                                     .ec2MetadataDisabledEnvVar("false"))
                 .expectedResolvedMode(DefaultsMode.CROSS_REGION),
 
+            // Imdsv2 disabled, should not query ImdsV2 and use fallback mode
+            new TestData().clientRegion(Region.US_EAST_1)
+                          .awsDefaultRegionEnvVar("us-west-2")
+                          .ec2MetadataConfig(new Ec2MetadataConfig().region("us-west-2")
+                                                                    .imdsAvailable(true)
+                                                                    .ec2MetadataDisabledEnvVar("true"))
+                .expectedResolvedMode(DefaultsMode.STANDARD),
+
+            // Imdsv2 not available, should use fallback mode.
             new TestData().clientRegion(Region.US_EAST_1)
                           .awsDefaultRegionEnvVar("us-west-2")
                           .ec2MetadataConfig(new Ec2MetadataConfig().imdsAvailable(false))
@@ -94,6 +110,7 @@ public void methodSetup() {
 
     @After
     public void cleanUp() {
+        EC2MetadataUtils.clearCache();
         wireMock.resetAll();
         ENVIRONMENT_VARIABLE_HELPER.reset();
         System.clearProperty(JavaSystemSetting.JAVA_VENDOR.property());
@@ -143,23 +160,10 @@ public void stubSuccessfulResponse(String region) {
         stubFor(put("/latest/api/token")
                     .willReturn(aResponse().withStatus(200).withBody("token")));
 
-
-        stubFor(get("/latest/dynamic/instance-identity/document")
-                    .willReturn(aResponse().withStatus(200).withBody(constructInstanceInfo(region))));
+        stubFor(get("/latest/meta-data/placement/region")
+                    .willReturn(aResponse().withStatus(200).withBody(region)));
     }
 
-    private String constructInstanceInfo(String region) {
-        return String.format("{"
-                             + "\"pendingTime\":\"2014-08-07T22:07:46Z\","
-                             + "\"instanceType\":\"m1.small\","
-                             + "\"imageId\":\"ami-123456\","
-                             + "\"instanceId\":\"i-123456\","
-                             + "\"region\":\"%s\","
-                             + "\"version\":\"2010-08-31\""
-                             + "}", region);
-    }
-
-
     private static final class TestData {
         private Region clientRegion;
         private String javaVendorProperty;

core/regions/src/main/java/software/amazon/awssdk/regions/internal/util/EC2MetadataUtils.java

@@ -39,7 +39,15 @@
 import software.amazon.awssdk.regions.util.ResourcesEndpointProvider;
 
 /**
- * Utility class for retrieving Amazon EC2 instance metadata.<br>
+
+ *
+ * Utility class for retrieving Amazon EC2 instance metadata.
+ *
+ * <p>
+ * <b>Note</b>: this is an internal API subject to change. Users of the SDK
+ * should not depend on this.
+ *
+ * <p>
  * You can use the data to build more generic AMIs that can be modified by
  * configuration files supplied at launch time. For example, if you run web
  * servers for various small businesses, they can all use the same AMI and
@@ -361,7 +369,7 @@ public static List<String> getItems(String path, int tries) {
     }
 
     @SdkTestInternalApi
-    static void clearCache() {
+    public static void clearCache() {
         CACHE.clear();
     }
 
@@ -391,6 +399,11 @@ private static List<String> getItems(String path, int tries, boolean slurp) {
             log.warn("Unable to retrieve the requested metadata.");
             return null;
         } catch (IOException | URISyntaxException | RuntimeException e) {
+            // If there is no retry available, just throw exception instead of pausing.
+            if (tries - 1 == 0) {
+                throw SdkClientException.builder().message("Unable to contact EC2 metadata service.").cause(e).build();
+            }
+
             // Retry on any other exceptions
             int pause = (int) (Math.pow(2, DEFAULT_QUERY_RETRIES - tries) * MINIMUM_RETRY_WAIT_TIME_MILLISECONDS);
             try {
@@ -427,19 +440,30 @@ public static String getToken() {
         }
     }
 
-
     private static String fetchData(String path) {
         return fetchData(path, false);
     }
 
     private static String fetchData(String path, boolean force) {
+        return fetchData(path, force, DEFAULT_QUERY_RETRIES);
+    }
+
+    /**
+     * Fetch data using the given path
+     *
+     * @param path the path
+     * @param force whether to force to override the value in the cache
+     * @param attempts the number of attempts that should be executed.
+     * @return the value retrieved from the path
+     */
+    public static String fetchData(String path, boolean force, int attempts) {
         if (SdkSystemSetting.AWS_EC2_METADATA_DISABLED.getBooleanValueOrThrow()) {
             throw SdkClientException.builder().message("EC2 metadata usage is disabled.").build();
         }
 
         try {
             if (force || !CACHE.containsKey(path)) {
-                CACHE.put(path, getData(path));
+                CACHE.put(path, getData(path, attempts));
             }
             return CACHE.get(path);
         } catch (SdkClientException e) {

core/regions/src/test/java/software/amazon/awssdk/regions/internal/util/EC2MetadataUtilsTest.java

@@ -24,7 +24,9 @@
 import static com.github.tomakehurst.wiremock.client.WireMock.stubFor;
 import static com.github.tomakehurst.wiremock.client.WireMock.urlPathEqualTo;
 import static org.assertj.core.api.Assertions.assertThat;
+
 import com.github.tomakehurst.wiremock.client.WireMock;
+import com.github.tomakehurst.wiremock.http.Fault;
 import com.github.tomakehurst.wiremock.junit.WireMockRule;
 import org.junit.Before;
 import org.junit.Rule;
@@ -131,4 +133,17 @@ public void getAmiId_queriesTokenResource_400Error_throws() {
 
         EC2MetadataUtils.getAmiId();
     }
+
+    @Test
+    public void fetchDataWithAttemptNumber_ioError_shouldHonor() {
+        int attempts = 1;
+        thrown.expect(SdkClientException.class);
+        thrown.expectMessage("Unable to contact EC2 metadata service");
+
+        stubFor(put(urlPathEqualTo(TOKEN_RESOURCE_PATH)).willReturn(aResponse().withBody("some-token")));;
+        stubFor(get(urlPathEqualTo(AMI_ID_RESOURCE)).willReturn(aResponse().withFault(Fault.CONNECTION_RESET_BY_PEER)));
+
+        EC2MetadataUtils.fetchData(AMI_ID_RESOURCE, false, attempts);
+        WireMock.verify(attempts, getRequestedFor(urlPathEqualTo(AMI_ID_RESOURCE)));
+    }
 }