* Provides an easy-to-use programming model for processing data using Amazon Kinesis
* Helps with scale-out and fault-tolerant processing
## Getting Started
1.**Sign up for AWS**— Before you begin, you need an AWS account. For more information about creating an AWS account and retrieving your AWS credentials, see [AWS Account and Credentials][docs-signup] in the AWS SDK for Java Developer Guide.
1.**Sign up for Amazon Kinesis**— Go to the Amazon Kinesis console to sign up for the service and create an Amazon Kinesis stream. For more information, see [Create an Amazon Kinesis Stream][kinesis-guide-create] in the Amazon Kinesis Developer Guide.
1.**Minimum requirements**— To use the Amazon Kinesis Client Library, you'll need **Java 1.7+**. For more information about Amazon Kinesis Client Library requirements, see [Before You Begin][kinesis-guide-begin] in the Amazon Kinesis Developer Guide.
1.**Using the Amazon Kinesis Client Library**— The best way to get familiar with the Amazon Kinesis Client Library is to read [Developing Record Consumer Applications][kinesis-guide-applications] in the Amazon Kinesis Developer Guide.
## Building from Source
After you've downloaded the code from GitHub, you can build it using Maven. To disable GPG signing in the build, use this command: `mvn clean install -Dgpg.skip=true`
For producer-side developers using the **[Kinesis Producer Library (KPL)][kinesis-guide-kpl]**, the KCL integrates without additional effort. When the KCL retrieves an aggregated Amazon Kinesis record consisting of multiple KPL user records, it will automatically invoke the KPL to extract the individual user records before returning them to the user.
To make it easier for developers to write record processors in other languages, we have implemented a Java based daemon, called MultiLangDaemon that does all the heavy lifting. Our approach has the daemon spawn a sub-process, which in turn runs the record processor, which can be written in any language. The MultiLangDaemon process and the record processor sub-process communicate with each other over [STDIN and STDOUT using a defined protocol][multi-lang-protocol]. There will be a one to one correspondence amongst record processors, child processes, and shards. For Python developers specifically, we have abstracted these implementation details away and [expose an interface][kclpy] that enables you to focus on writing record processing logic in Python. This approach enables KCL to be language agnostic, while providing identical features and similar parallel processing model across all languages.
Prefetching will retrieve and queue additional records from Kinesis while the application is processing existing records.
Prefetching can be enabled by setting [`dataFetchingStrategy`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1317) to `PREFETCH_CACHED`. Once enabled an additional fetching thread will be started to retrieve records from Kinesis. Retrieved records will be held in a queue until the application is ready to process them.
Pre-fetching supports the following configuration values:
| Name | Default | Description |
| ---- | ------- | ----------- |
| [`dataFetchingStrategy`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1317) | `DEFAULT` | Which data fetching strategy to use |
| [`maxPendingProcessRecordsInput`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1296) | 3 | The maximum number of process records input that can be queued |
| [`maxCacheByteSize`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1307) | 8 MiB | The maximum number of bytes that can be queued |
| [`maxRecordsCount`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1326) | 30,000 | The maximum number of records that can be queued |
| [`idleMillisBetweenCalls`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L1353) | 1,500 ms | The amount of time to wait between calls to Kinesis |
* Only advance the shard iterator for the accepted response.
This fixes a race condition in the `KinesisDataFetcher` when it's being used to make asynchronous requests. The shard iterator is now only advanced when the retriever calls `DataFetcherResult#accept()`.
* Call shutdown on the retriever when the record processor is being shutdown
This fixes a bug that could leak threads if using the [`AsynchronousGetRecordsRetrievalStrategy`](https://github.com/awslabs/amazon-kinesis-client/blob/9a82b6bd05b3c9c5f8581af007141fa6d5f0fc4e/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/AsynchronousGetRecordsRetrievalStrategy.java#L42) is being used.
The asynchronous retriever is only used when [`KinesisClientLibConfiguration#retryGetRecordsInSeconds`](https://github.com/awslabs/amazon-kinesis-client/blob/01d2688bc6e68fd3fe5cb698cb65299d67ac930d/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L227), and [`KinesisClientLibConfiguration#maxGetRecordsThreadPool`](https://github.com/awslabs/amazon-kinesis-client/blob/01d2688bc6e68fd3fe5cb698cb65299d67ac930d/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/KinesisClientLibConfiguration.java#L230) are set.
Applications can now set a pending checkpoint, before completing the checkpoint operation. Once the application has completed its checkpoint steps, the final checkpoint will clear the pending checkpoint.
Should the checkpoint fail the attempted sequence number is provided in the [`InitializationInput#getPendingCheckpointSequenceNumber`](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/types/InitializationInput.java#L81) otherwise the value will be null.
* Support timeouts, and retry for GetRecords calls.
Applications can now set timeouts for GetRecord calls to Kinesis. As part of setting the timeout, the application must also provide a thread pool size for concurrent requests.
When writes, or reads, to the lease table are throttled a warning will be emitted. If you're seeing this warning you should increase the IOPs for your lease table to prevent processing delays.
* Support configuring the graceful shutdown timeout for MultiLang Clients
This adds support for setting the timeout that the Java process will wait for the MutliLang client to complete graceful shutdown. The timeout can be configured by adding `shutdownGraceMillis` to the properties file set to the number of milliseconds to wait.
* Support timeouts for calls to the MultiLang Daemon
This adds support for setting a timeout when dispatching records to the client record processor. If the record processor doesn't respond within the timeout the parent Java process will be terminated. This is a temporary fix to handle cases where the KCL becomes blocked while waiting for a client record processor.
The timeout for the this can be set by adding `timeoutInSeconds = <timeout value>`. The default for this is no timeout.
__Setting this can cause the KCL to exit suddenly, before using this ensure that you have an automated restart for your application__
The MultiLangDaemon has been upgraded to use the v2 interfaces, which allows access to enhanced checkpointing, and more information during record processor initialization. The MultiLangDaemon clients must be updated before they can take advantage of these new features.
* Applications can now request a graceful shutdown, and record processors that implement the IShutdownNotificationAware will be given a chance to checkpoint before being shutdown.
* This adds a [new interface](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/interfaces/v2/IShutdownNotificationAware.java), and a [new method on Worker](https://github.com/awslabs/amazon-kinesis-client/blob/master/src/main/java/com/amazonaws/services/kinesis/clientlibrary/lib/worker/Worker.java#L539).
* Add support for time based iterators ([See GetShardIterator Documentation](http://docs.aws.amazon.com/kinesis/latest/APIReference/API_GetShardIterator.html))
The `KinesisClientLibconfiguration` now supports providing a `ShardPrioritization` strategy. This strategy controls how the `Worker` determines which `ShardConsumer` to call next. This can improve processing for streams that split often, such as DynamoDB Streams.
* Remove direct dependency on `aws-java-sdk-core`, to allow independent versioning.
* Support for specifying max leases per worker and max leases to steal at a time.
* Support for specifying initial DynamoDB table read and write capacity.
* Support for parallel lease renewal.
* Support for graceful worker shutdown.
* Change DefaultCWMetricsPublisher log level to debug. [PR # 49](https://github.com/awslabs/amazon-kinesis-client/pull/49)
* Avoid NPE in MLD record processor shutdown if record processor was not initialized. [Issue # 29](https://github.com/awslabs/amazon-kinesis-client/issues/29)
* Expose [approximateArrivalTimestamp](http://docs.aws.amazon.com/kinesis/latest/APIReference/API_GetRecords.html) for Records in processRecords API call.
* Restores compatibility with [dynamodb-streams-kinesis-adapter](https://github.com/awslabs/dynamodb-streams-kinesis-adapter) (which was broken in 1.4.0).
* **Multi-Language Support** — Amazon KCL now supports implementing record processors in any language by communicating with the daemon over [STDIN and STDOUT][multi-lang-protocol]. Python developers can directly use the [Amazon Kinesis Client Library for Python][kclpy] to write their data processing applications.
* **Checkpointing at a specific sequence number** — The IRecordProcessorCheckpointer interface now supports checkpointing at a sequence number specified by the record processor.
* **Set region** — KinesisClientLibConfiguration now supports setting the region name to indicate the location of the Amazon Kinesis service. The Amazon DynamoDB table and Amazon CloudWatch metrics associated with your application will also use this region setting.
