Add retry strategy for throttling in clients

This is expected for Review Readiness of the Uluru handlers.

aws-transfer-server/src/main/java/software/amazon/transfer/server/clients/ClientBuilder.java

@@ -1,16 +1,36 @@
 package software.amazon.transfer.server.clients;
 
+import java.time.Duration;
+
+import software.amazon.awssdk.awscore.retry.AwsRetryStrategy;
+import software.amazon.awssdk.core.client.config.ClientOverrideConfiguration;
+import software.amazon.awssdk.core.internal.retry.SdkDefaultRetrySetting;
+import software.amazon.awssdk.retries.api.BackoffStrategy;
+import software.amazon.awssdk.retries.api.RetryStrategy;
 import software.amazon.awssdk.services.transfer.TransferClient;
 import software.amazon.cloudformation.LambdaWrapper;
 
 /** Create a TransferClient instance. */
 public class ClientBuilder {
+    private static final BackoffStrategy TRANSFER_BACKOFF_THROTTLING_STRATEGY =
+            BackoffStrategy.exponentialDelay(Duration.ofMillis(2000), SdkDefaultRetrySetting.MAX_BACKOFF);
+
+    private static final RetryStrategy TRANSFER_RETRY_STRATEGY = AwsRetryStrategy.adaptiveRetryStrategy().toBuilder()
+            .backoffStrategy(TRANSFER_BACKOFF_THROTTLING_STRATEGY)
+            .maxAttempts(4)
+            .build();
+
     /**
      * Returns the TransferClient instance.
      *
      * @return the TransferClient instance.
      */
     public static TransferClient getClient() {
-        return TransferClient.builder().httpClient(LambdaWrapper.HTTP_CLIENT).build();
+        return TransferClient.builder()
+                .httpClient(LambdaWrapper.HTTP_CLIENT)
+                .overrideConfiguration(ClientOverrideConfiguration.builder()
+                        .retryStrategy(TRANSFER_RETRY_STRATEGY)
+                        .build())
+                .build();
     }
 }

aws-transfer-server/src/main/java/software/amazon/transfer/server/clients/Ec2ClientBuilder.java

@@ -1,16 +1,36 @@
 package software.amazon.transfer.server.clients;
 
+import java.time.Duration;
+
+import software.amazon.awssdk.awscore.retry.AwsRetryStrategy;
+import software.amazon.awssdk.core.client.config.ClientOverrideConfiguration;
+import software.amazon.awssdk.core.internal.retry.SdkDefaultRetrySetting;
+import software.amazon.awssdk.retries.api.BackoffStrategy;
+import software.amazon.awssdk.retries.api.RetryStrategy;
 import software.amazon.awssdk.services.ec2.Ec2Client;
 import software.amazon.cloudformation.LambdaWrapper;
 
 /** Create an Ec2Client instance. */
 public class Ec2ClientBuilder {
+    private static final BackoffStrategy EC2_BACKOFF_THROTTLING_STRATEGY =
+            BackoffStrategy.exponentialDelay(Duration.ofMillis(2000), SdkDefaultRetrySetting.MAX_BACKOFF);
+
+    private static final RetryStrategy EC2_RETRY_STRATEGY = AwsRetryStrategy.adaptiveRetryStrategy().toBuilder()
+            .backoffStrategy(EC2_BACKOFF_THROTTLING_STRATEGY)
+            .maxAttempts(4)
+            .build();
+
     /**
      * Returns the Ec2Client instance.
      *
      * @return the Ec2Client instance.
      */
     public static Ec2Client getClient() {
-        return Ec2Client.builder().httpClient(LambdaWrapper.HTTP_CLIENT).build();
+        return Ec2Client.builder()
+                .httpClient(LambdaWrapper.HTTP_CLIENT)
+                .overrideConfiguration(ClientOverrideConfiguration.builder()
+                        .retryStrategy(EC2_RETRY_STRATEGY)
+                        .build())
+                .build();
     }
 }

aws-transfer-user/src/main/java/software/amazon/transfer/user/clients/ClientBuilder.java

@@ -1,12 +1,36 @@
 package software.amazon.transfer.user.clients;
 
+import java.time.Duration;
+
+import software.amazon.awssdk.awscore.retry.AwsRetryStrategy;
+import software.amazon.awssdk.core.client.config.ClientOverrideConfiguration;
+import software.amazon.awssdk.core.internal.retry.SdkDefaultRetrySetting;
+import software.amazon.awssdk.retries.api.BackoffStrategy;
+import software.amazon.awssdk.retries.api.RetryStrategy;
 import software.amazon.awssdk.services.transfer.TransferClient;
 import software.amazon.cloudformation.LambdaWrapper;
 
-public final class ClientBuilder {
-    private ClientBuilder() {}
+/** Create a TransferClient instance. */
+public class ClientBuilder {
+    private static final BackoffStrategy TRANSFER_BACKOFF_THROTTLING_STRATEGY =
+            BackoffStrategy.exponentialDelay(Duration.ofMillis(2000), SdkDefaultRetrySetting.MAX_BACKOFF);
+
+    private static final RetryStrategy TRANSFER_RETRY_STRATEGY = AwsRetryStrategy.adaptiveRetryStrategy().toBuilder()
+            .backoffStrategy(TRANSFER_BACKOFF_THROTTLING_STRATEGY)
+            .maxAttempts(4)
+            .build();
 
+    /**
+     * Returns the TransferClient instance.
+     *
+     * @return the TransferClient instance.
+     */
     public static TransferClient getClient() {
-        return TransferClient.builder().httpClient(LambdaWrapper.HTTP_CLIENT).build();
+        return TransferClient.builder()
+                .httpClient(LambdaWrapper.HTTP_CLIENT)
+                .overrideConfiguration(ClientOverrideConfiguration.builder()
+                        .retryStrategy(TRANSFER_RETRY_STRATEGY)
+                        .build())
+                .build();
     }
 }