# Develop KCL 1.x consumers
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can develop a consumer application for Amazon Kinesis Data Streams using the Kinesis Client Library (KCL).
For more information about KCL, see [About KCL (previous versions)](shared-throughput-kcl-consumers.md#shared-throughput-kcl-consumers-overview).
Choose from the following topics depending on the option you want to use.
**Topics**
+ [Develop a Kinesis Client Library consumer in Java](kinesis-record-processor-implementation-app-java.md)
+ [Develop a Kinesis Client Library consumer in Node.js](kinesis-record-processor-implementation-app-nodejs.md)
+ [Develop a Kinesis Client Library consumer in .NET](kinesis-record-processor-implementation-app-dotnet.md)
+ [Develop a Kinesis Client Library consumer in Python](kinesis-record-processor-implementation-app-py.md)
+ [Develop a Kinesis Client Library consumer in Ruby](kinesis-record-processor-implementation-app-ruby.md)
# Develop a Kinesis Client Library consumer in Java
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can use the Kinesis Client Library (KCL) to build applications that process data from your Kinesis data streams. The Kinesis Client Library is available in multiple languages. This topic discusses Java. To view the Javadoc reference, see the [AWS Javadoc topic for Class AmazonKinesisClient](https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/kinesis/AmazonKinesisClient.html).
To download the Java KCL from GitHub, go to [Kinesis Client Library (Java)](https://github.com/awslabs/amazon-kinesis-client). To locate the Java KCL on Apache Maven, go to the [KCL search results](https://search.maven.org/#search|ga|1|amazon-kinesis-client) page. To download sample code for a Java KCL consumer application from GitHub, go to the [KCL for Java sample project](https://github.com/aws/aws-sdk-java/tree/master/src/samples/AmazonKinesis) page on GitHub.
The sample application uses [Apache Commons Logging](http://commons.apache.org/proper/commons-logging/guide.html). You can change the logging configuration in the static `configure` method defined in the `AmazonKinesisApplicationSample.java` file. For more information about how to use Apache Commons Logging with Log4j and AWS Java applications, see [Logging with Log4j](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/java-dg-logging.html) in the *AWS SDK for Java Developer Guide*.
You must complete the following tasks when implementing a KCL consumer application in Java:
**Topics**
+ [Implement the IRecordProcessor methods](#kinesis-record-processor-implementation-interface-java)
+ [Implement a class factory for the IRecordProcessor interface](#kinesis-record-processor-implementation-factory-java)
+ [Create a worker](#kcl-java-worker)
+ [Modify the configuration properties](#kinesis-record-processor-initialization-java)
+ [Migrate to Version 2 of the record processor interface](#kcl-java-v2-migration)
## Implement the IRecordProcessor methods
The KCL currently supports two versions of the `IRecordProcessor` interface:The original interface is available with the first version of the KCL, and version 2 is available starting with KCL version 1.5.0. Both interfaces are fully supported. Your choice depends on your specific scenario requirements. Refer to your locally built Javadocs or the source code to see all the differences. The following sections outline the minimal implementation for getting started.
**Topics**
+ [Original Interface (Version 1)](#kcl-java-interface-original)
+ [Updated interface (Version 2)](#kcl-java-interface-v2)
### Original Interface (Version 1)
The original `IRecordProcessor` interface (`package com.amazonaws.services.kinesis.clientlibrary.interfaces`) exposes the following record processor methods that your consumer must implement. The sample provides implementations that you can use as a starting point (see `AmazonKinesisApplicationSampleRecordProcessor.java`).
```
public void initialize(String shardId)
public void processRecords(List records, IRecordProcessorCheckpointer checkpointer)
public void shutdown(IRecordProcessorCheckpointer checkpointer, ShutdownReason reason)
```
**initialize**
The KCL calls the `initialize` method when the record processor is instantiated, passing a specific shard ID as a parameter. This record processor processes only this shard and typically, the reverse is also true (this shard is processed only by this record processor). However, your consumer should account for the possibility that a data record might be processed more than one time. Kinesis Data Streams has *at least once* semantics, meaning that every data record from a shard is processed at least one time by a worker in your consumer. For more information about cases in which a particular shard may be processed by more than one worker, see [Use resharding, scaling, and parallel processing to change the number of shards](kinesis-record-processor-scaling.md).
```
public void initialize(String shardId)
```
**processRecords**
The KCL calls the `processRecords` method, passing a list of data record from the shard specified by the `initialize(shardId)` method. The record processor processes the data in these records according to the semantics of the consumer. For example, the worker might perform a transformation on the data and then store the result in an Amazon Simple Storage Service (Amazon S3) bucket.
```
public void processRecords(List records, IRecordProcessorCheckpointer checkpointer)
```
In addition to the data itself, the record also contains a sequence number and partition key. The worker can use these values when processing the data. For example, the worker could choose the S3 bucket in which to store the data based on the value of the partition key. The `Record` class exposes the following methods that provide access to the record's data, sequence number, and partition key.
```
record.getData()
record.getSequenceNumber()
record.getPartitionKey()
```
In the sample, the private method `processRecordsWithRetries` has code that shows how a worker can access the record's data, sequence number, and partition key.
Kinesis Data Streams requires the record processor to keep track of the records that have already been processed in a shard. The KCL takes care of this tracking for you by passing a checkpointer (`IRecordProcessorCheckpointer`) to `processRecords`. The record processor calls the `checkpoint` method on this interface to inform the KCL of how far it has progressed in processing the records in the shard. If the worker fails, the KCL uses this information to restart the processing of the shard at the last known processed record.
For a split or merge operation, the KCL won't start processing the new shards until the processors for the original shards have called `checkpoint` to signal that all processing on the original shards is complete.
If you don't pass a parameter, the KCL assumes that the call to `checkpoint` means that all records have been processed, up to the last record that was passed to the record processor. Therefore, the record processor should call `checkpoint` only after it has processed all the records in the list that was passed to it. Record processors do not need to call `checkpoint` on each call to `processRecords`. A processor could, for example, call `checkpoint` on every third call to `processRecords`. You can optionally specify the exact sequence number of a record as a parameter to `checkpoint`. In this case, the KCL assumes that all records have been processed up to that record only.
In the sample, the private method `checkpoint` shows how to call `IRecordProcessorCheckpointer.checkpoint` using the appropriate exception handling and retry logic.
The KCL relies on `processRecords` to handle any exceptions that arise from processing the data records. If an exception is thrown from `processRecords`, the KCL skips over the data records that were passed before the exception. That is, these records are not re-sent to the record processor that threw the exception or to any other record processor in the consumer.
**shutdown**
The KCL calls the `shutdown` method either when processing ends (the shutdown reason is `TERMINATE`) or the worker is no longer responding (the shutdown reason is `ZOMBIE`).
```
public void shutdown(IRecordProcessorCheckpointer checkpointer, ShutdownReason reason)
```
Processing ends when the record processor does not receive any further records from the shard, because either the shard was split or merged, or the stream was deleted.
The KCL also passes a `IRecordProcessorCheckpointer` interface to `shutdown`. If the shutdown reason is `TERMINATE`, the record processor should finish processing any data records, and then call the `checkpoint` method on this interface.
### Updated interface (Version 2)
The updated `IRecordProcessor` interface (`package com.amazonaws.services.kinesis.clientlibrary.interfaces.v2`) exposes the following record processor methods that your consumer must implement:
```
void initialize(InitializationInput initializationInput)
void processRecords(ProcessRecordsInput processRecordsInput)
void shutdown(ShutdownInput shutdownInput)
```
All of the arguments from the original version of the interface are accessible through get methods on the container objects. For example, to retrieve the list of records in `processRecords()`, you can use `processRecordsInput.getRecords()`.
As of version 2 of this interface (KCL 1.5.0 and later), the following new inputs are available in addition to the inputs provided by the original interface:
starting sequence number
In the `InitializationInput` object passed to the `initialize()` operation, the starting sequence number from which records would be provided to the record processor instance. This is the sequence number that was last checkpointed by the record processor instance previously processing the same shard. This is provided in case your application needs this information.
pending checkpoint sequence number
In the `InitializationInput` object passed to the `initialize()` operation, the pending checkpoint sequence number (if any) that could not be committed before the previous record processor instance stopped.
## Implement a class factory for the IRecordProcessor interface
You also need to implement a factory for the class that implements the record processor methods. When your consumer instantiates the worker, it passes a reference to this factory.
The sample implements the factory class in the file `AmazonKinesisApplicationSampleRecordProcessorFactory.java` using the original record processor interface. If you want the class factory to create version 2 record processors, use the package name `com.amazonaws.services.kinesis.clientlibrary.interfaces.v2`.
```
public class SampleRecordProcessorFactory implements IRecordProcessorFactory {
/**
* Constructor.
*/
public SampleRecordProcessorFactory() {
super();
}
/**
* {@inheritDoc}
*/
@Override
public IRecordProcessor createProcessor() {
return new SampleRecordProcessor();
}
}
```
## Create a worker
As discussed in [Implement the IRecordProcessor methods](#kinesis-record-processor-implementation-interface-java), there are two versions of the KCL record processor interface to choose from, which affects how you would create a worker. The original record processor interface uses the following code structure to create a worker:
```
final KinesisClientLibConfiguration config = new KinesisClientLibConfiguration(...)
final IRecordProcessorFactory recordProcessorFactory = new RecordProcessorFactory();
final Worker worker = new Worker(recordProcessorFactory, config);
```
With version 2 of the record processor interface, you can use `Worker.Builder` to create a worker without needing to worry about which constructor to use and the order of the arguments. The updated record processor interface uses the following code structure to create a worker:
```
final KinesisClientLibConfiguration config = new KinesisClientLibConfiguration(...)
final IRecordProcessorFactory recordProcessorFactory = new RecordProcessorFactory();
final Worker worker = new Worker.Builder()
.recordProcessorFactory(recordProcessorFactory)
.config(config)
.build();
```
## Modify the configuration properties
The sample provides default values for configuration properties. This configuration data for the worker is then consolidated in a `KinesisClientLibConfiguration` object. This object and a reference to the class factory for `IRecordProcessor` are passed in the call that instantiates the worker. You can override any of these properties with your own values using a Java properties file (see `AmazonKinesisApplicationSample.java`).
### Application name
The KCL requires an application name that is unique across your applications, and across Amazon DynamoDB tables in the same Region. It uses the application name configuration value in the following ways:
+ All workers associated with this application name are assumed to be working together on the same stream. These workers may be distributed on multiple instances. If you run an additional instance of the same application code, but with a different application name, the KCL treats the second instance as an entirely separate application that is also operating on the same stream.
+ The KCL creates a DynamoDB table with the application name and uses the table to maintain state information (such as checkpoints and worker-shard mapping) for the application. Each application has its own DynamoDB table. For more information, see [Use a lease table to track the shards processed by the KCL consumer application](shared-throughput-kcl-consumers.md#shared-throughput-kcl-consumers-leasetable).
### Set up credentials
You must make your AWS credentials available to one of the credential providers in the default credential providers chain. For example, if you are running your consumer on an EC2 instance, we recommend that you launch the instance with an IAM role. AWS credentials that reflect the permissions associated with this IAM role are made available to applications on the instance through its instance metadata. This is the most secure way to manage credentials for a consumer running on an EC2 instance.
The sample application first attempts to retrieve IAM credentials from instance metadata:
```
credentialsProvider = new InstanceProfileCredentialsProvider();
```
If the sample application cannot obtain credentials from the instance metadata, it attempts to retrieve credentials from a properties file:
```
credentialsProvider = new ClasspathPropertiesFileCredentialsProvider();
```
For more information about instance metadata, see [Instance Metadata](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html) in the *Amazon EC2 User Guide*.
### Use the worker ID for multiple instances
The sample initialization code creates an ID for the worker, `workerId`, using the name of the local computer and appending a globally unique identifier as shown in the following code snippet. This approach supports the scenario of multiple instances of the consumer application running on a single computer.
```
String workerId = InetAddress.getLocalHost().getCanonicalHostName() + ":" + UUID.randomUUID();
```
## Migrate to Version 2 of the record processor interface
If you want to migrate code that uses the original interface, in addition to the steps described previously, the following steps are required:
1. Change your record processor class to import the version 2 record processor interface:
```
import com.amazonaws.services.kinesis.clientlibrary.interfaces.v2.IRecordProcessor;
```
1. Change the references to inputs to use `get` methods on the container objects. For example, in the `shutdown()` operation, change "`checkpointer`" to "`shutdownInput.getCheckpointer()`".
1. Change your record processor factory class to import the version 2 record processor factory interface:
```
import com.amazonaws.services.kinesis.clientlibrary.interfaces.v2.IRecordProcessorFactory;
```
1. Change the construction of the worker to use `Worker.Builder`. For example:
```
final Worker worker = new Worker.Builder()
.recordProcessorFactory(recordProcessorFactory)
.config(config)
.build();
```
# Develop a Kinesis Client Library consumer in Node.js
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can use the Kinesis Client Library (KCL) to build applications that process data from your Kinesis data streams. The Kinesis Client Library is available in multiple languages. This topic discusses Node.js.
The KCL is a Java library; support for languages other than Java is provided using a multi-language interface called the *MultiLangDaemon*. This daemon is Java-based and runs in the background when you are using a KCL language other than Java. Therefore, if you install the KCL for Node.js and write your consumer app entirely in Node.js, you still need Java installed on your system because of the MultiLangDaemon. Further, MultiLangDaemon has some default settings you may need to customize for your use case, for example, the AWS Region that it connects to. For more information about the MultiLangDaemon on GitHub, go to the [KCL MultiLangDaemon project](https://github.com/awslabs/amazon-kinesis-client/tree/v1.x/src/main/java/com/amazonaws/services/kinesis/multilang) page.
To download the Node.js KCL from GitHub, go to [Kinesis Client Library (Node.js)](https://github.com/awslabs/amazon-kinesis-client-nodejs).
**Sample Code Downloads**
There are two code samples available for KCL in Node.js:
+ [basic-sample](https://github.com/awslabs/amazon-kinesis-client-nodejs/tree/master/samples/basic_sample)
Used in the following sections to illustrate the fundamentals of building a KCL consumer application in Node.js.
+ [click-stream-sample](https://github.com/awslabs/amazon-kinesis-client-nodejs/tree/master/samples/click_stream_sample)
Slightly more advanced and uses a real-world scenario, after you have familiarized yourself with the basic sample code. This sample is not discussed here but has a README file with more information.
You must complete the following tasks when implementing a KCL consumer application in Node.js:
**Topics**
+ [Implement the record processor](#kinesis-record-processor-implementation-interface-nodejs)
+ [Modify the configuration properties](#kinesis-record-processor-initialization-nodejs)
## Implement the record processor
The simplest possible consumer using the KCL for Node.js must implement a `recordProcessor` function, which in turn contains the functions `initialize`, `processRecords`, and `shutdown`. The sample provides an implementation that you can use as a starting point (see `sample_kcl_app.js`).
```
function recordProcessor() {
// return an object that implements initialize, processRecords and shutdown functions.}
```
**initialize**
The KCL calls the `initialize` function when the record processor starts. This record processor processes only the shard ID passed as `initializeInput.shardId`, and typically, the reverse is also true (this shard is processed only by this record processor). However, your consumer should account for the possibility that a data record might be processed more than one time. This is because Kinesis Data Streams has *at least once* semantics, meaning that every data record from a shard is processed at least one time by a worker in your consumer. For more information about cases in which a particular shard might be processed by more than one worker, see [Use resharding, scaling, and parallel processing to change the number of shards](kinesis-record-processor-scaling.md).
```
initialize: function(initializeInput, completeCallback)
```
**processRecords**
The KCL calls this function with input that contains a list of data records from the shard specified to the `initialize` function. The record processor that you implement processes the data in these records according to the semantics of your consumer. For example, the worker might perform a transformation on the data and then store the result in an Amazon Simple Storage Service (Amazon S3) bucket.
```
processRecords: function(processRecordsInput, completeCallback)
```
In addition to the data itself, the record also contains a sequence number and partition key, which the worker can use when processing the data. For example, the worker could choose the S3 bucket in which to store the data based on the value of the partition key. The `record` dictionary exposes the following key-value pairs to access the record's data, sequence number, and partition key:
```
record.data
record.sequenceNumber
record.partitionKey
```
Note that the data is Base64-encoded.
In the basic sample, the function `processRecords` has code that shows how a worker can access the record's data, sequence number, and partition key.
Kinesis Data Streams requires the record processor to keep track of the records that have already been processed in a shard. The KCL takes care of this tracking for with a `checkpointer` object passed as `processRecordsInput.checkpointer`. Your record processor calls the `checkpointer.checkpoint` function to inform the KCL how far it has progressed in processing the records in the shard. In the event that the worker fails, the KCL uses this information when you restart the processing of the shard so that it continues from the last known processed record.
For a split or merge operation, the KCL doesn't start processing the new shards until the processors for the original shards have called `checkpoint` to signal that all processing on the original shards is complete.
If you don't pass the sequence number to the `checkpoint` function, the KCL assumes that the call to `checkpoint` means that all records have been processed, up to the last record that was passed to the record processor. Therefore, the record processor should call `checkpoint` **only** after it has processed all the records in the list that was passed to it. Record processors do not need to call `checkpoint` on each call to `processRecords`. A processor could, for example, call `checkpoint` on every third call, or some event external to your record processor, such as a custom verification/validation service you've implemented.
You can optionally specify the exact sequence number of a record as a parameter to `checkpoint`. In this case, the KCL assumes that all records have been processed up to that record only.
The basic sample application shows the simplest possible call to the `checkpointer.checkpoint` function. You can add other checkpointing logic you need for your consumer at this point in the function.
**shutdown**
The KCL calls the `shutdown` function either when processing ends (`shutdownInput.reason` is `TERMINATE`) or the worker is no longer responding (`shutdownInput.reason` is `ZOMBIE`).
```
shutdown: function(shutdownInput, completeCallback)
```
Processing ends when the record processor does not receive any further records from the shard, because either the shard was split or merged, or the stream was deleted.
The KCL also passes a `shutdownInput.checkpointer` object to `shutdown`. If the shutdown reason is `TERMINATE`, you should make sure that the record processor has finished processing any data records, and then call the `checkpoint` function on this interface.
## Modify the configuration properties
The sample provides default values for the configuration properties. You can override any of these properties with your own values (see `sample.properties` in the basic sample).
### Application name
The KCL requires an application that this is unique among your applications, and among Amazon DynamoDB tables in the same Region. It uses the application name configuration value in the following ways:
+ All workers associated with this application name are assumed to be working together on the same stream. These workers may be distributed on multiple instances. If you run an additional instance of the same application code, but with a different application name, the KCL treats the second instance as an entirely separate application that is also operating on the same stream.
+ The KCL creates a DynamoDB table with the application name and uses the table to maintain state information (such as checkpoints and worker-shard mapping) for the application. Each application has its own DynamoDB table. For more information, see [Use a lease table to track the shards processed by the KCL consumer application](shared-throughput-kcl-consumers.md#shared-throughput-kcl-consumers-leasetable).
### Set up credentials
You must make your AWS credentials available to one of the credential providers in the default credential providers chain. You can you use the `AWSCredentialsProvider` property to set a credentials provider. The `sample.properties` file must make your credentials available to one of the credentials providers in the [default credential providers chain](https://docs.aws.amazon.com/sdk-for-java/latest/reference/com/amazonaws/auth/DefaultAWSCredentialsProviderChain.html). If you are running your consumer on an Amazon EC2 instance, we recommend that you configure the instance with an IAM role. AWS credentials that reflect the permissions associated with this IAM role are made available to applications on the instance through its instance metadata. This is the most secure way to manage credentials for a consumer application running on an EC2 instance.
The following example configures KCL to process a Kinesis data stream named `kclnodejssample` using the record processor supplied in `sample_kcl_app.js`:
```
# The Node.js executable script
executableName = node sample_kcl_app.js
# The name of an Amazon Kinesis stream to process
streamName = kclnodejssample
# Unique KCL application name
applicationName = kclnodejssample
# Use default AWS credentials provider chain
AWSCredentialsProvider = DefaultAWSCredentialsProviderChain
# Read from the beginning of the stream
initialPositionInStream = TRIM_HORIZON
```
# Develop a Kinesis Client Library consumer in .NET
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can use the Kinesis Client Library (KCL) to build applications that process data from your Kinesis data streams. The Kinesis Client Library is available in multiple languages. This topic discusses .NET.
The KCL is a Java library; support for languages other than Java is provided using a multi-language interface called the *MultiLangDaemon*. This daemon is Java-based and runs in the background when you are using a KCL language other than Java. Therefore, if you install the KCL for .NET and write your consumer app entirely in .NET, you still need Java installed on your system because of the MultiLangDaemon. Further, MultiLangDaemon has some default settings you may need to customize for your use case, for example, the AWS Region that it connects to. For more information about the MultiLangDaemon on GitHub, go to the [KCL MultiLangDaemon project](https://github.com/awslabs/amazon-kinesis-client/tree/v1.x/src/main/java/com/amazonaws/services/kinesis/multilang) page.
To download the .NET KCL from GitHub, go to [Kinesis Client Library (.NET)](https://github.com/awslabs/amazon-kinesis-client-net). To download sample code for a .NET KCL consumer application, go to the [KCL for .NET sample consumer project](https://github.com/awslabs/amazon-kinesis-client-net/tree/master/SampleConsumer) page on GitHub.
You must complete the following tasks when implementing a KCL consumer application in .NET:
**Topics**
+ [Implement the IRecordProcessor class methods](#kinesis-record-processor-implementation-interface-dotnet)
+ [Modify the configuration properties](#kinesis-record-processor-initialization-dotnet)
## Implement the IRecordProcessor class methods
The consumer must implement the following methods for `IRecordProcessor`. The sample consumer provides implementations that you can use as a starting point (see the `SampleRecordProcessor` class in `SampleConsumer/AmazonKinesisSampleConsumer.cs`).
```
public void Initialize(InitializationInput input)
public void ProcessRecords(ProcessRecordsInput input)
public void Shutdown(ShutdownInput input)
```
**Initialize**
The KCL calls this method when the record processor is instantiated, passing a specific shard ID in the `input` parameter (`input.ShardId`). This record processor processes only this shard, and typically, the reverse is also true (this shard is processed only by this record processor). However, your consumer should account for the possibility that a data record might be processed more than one time. This is because Kinesis Data Streams has *at least once* semantics, meaning that every data record from a shard is processed at least one time by a worker in your consumer. For more information about cases in which a particular shard might be processed by more than one worker, see [Use resharding, scaling, and parallel processing to change the number of shards](kinesis-record-processor-scaling.md).
```
public void Initialize(InitializationInput input)
```
**ProcessRecords**
The KCL calls this method, passing a list of data records in the `input` parameter (`input.Records`) from the shard specified by the `Initialize` method. The record processor that you implement processes the data in these records according to the semantics of your consumer. For example, the worker might perform a transformation on the data and then store the result in an Amazon Simple Storage Service (Amazon S3) bucket.
```
public void ProcessRecords(ProcessRecordsInput input)
```
In addition to the data itself, the record also contains a sequence number and partition key. The worker can use these values when processing the data. For example, the worker could choose the S3 bucket in which to store the data based on the value of the partition key. The `Record` class exposes the following to access the record's data, sequence number, and partition key:
```
byte[] Record.Data
string Record.SequenceNumber
string Record.PartitionKey
```
In the sample, the method `ProcessRecordsWithRetries` has code that shows how a worker can access the record's data, sequence number, and partition key.
Kinesis Data Streams requires the record processor to keep track of the records that have already been processed in a shard. The KCL takes care of this tracking for you by passing a `Checkpointer` object to `ProcessRecords` (`input.Checkpointer`). The record processor calls the `Checkpointer.Checkpoint` method to inform the KCL of how far it has progressed in processing the records in the shard. If the worker fails, the KCL uses this information to restart the processing of the shard at the last known processed record.
For a split or merge operation, the KCL doesn't start processing the new shards until the processors for the original shards have called `Checkpointer.Checkpoint` to signal that all processing on the original shards is complete.
If you don't pass a parameter, the KCL assumes that the call to `Checkpointer.Checkpoint` signifies that all records have been processed, up to the last record that was passed to the record processor. Therefore, the record processor should call `Checkpointer.Checkpoint` only after it has processed all the records in the list that was passed to it. Record processors do not need to call `Checkpointer.Checkpoint` on each call to `ProcessRecords`. A processor could, for example, call `Checkpointer.Checkpoint` on every third or fourth call. You can optionally specify the exact sequence number of a record as a parameter to `Checkpointer.Checkpoint`. In this case, the KCL assumes that records have been processed only up to that record.
In the sample, the private method `Checkpoint(Checkpointer checkpointer)` shows how to call the `Checkpointer.Checkpoint` method using appropriate exception handling and retry logic.
The KCL for .NET handles exceptions differently from other KCL language libraries in that it does not handle any exceptions that arise from processing the data records. Any uncaught exceptions from user code crashes the program.
**Shutdown**
The KCL calls the `Shutdown` method either when processing ends (the shutdown reason is `TERMINATE`) or the worker is no longer responding (the shutdown `input.Reason` value is `ZOMBIE`).
```
public void Shutdown(ShutdownInput input)
```
Processing ends when the record processor does not receive any further records from the shard, because the shard was split or merged, or the stream was deleted.
The KCL also passes a `Checkpointer` object to `shutdown`. If the shutdown reason is `TERMINATE`, the record processor should finish processing any data records, and then call the `checkpoint` method on this interface.
## Modify the configuration properties
The sample consumer provides default values for the configuration properties. You can override any of these properties with your own values (see `SampleConsumer/kcl.properties`).
### Application name
The KCL requires an application that this is unique among your applications, and among Amazon DynamoDB tables in the same Region. It uses the application name configuration value in the following ways:
+ All workers associated with this application name are assumed to be working together on the same stream. These workers may be distributed on multiple instances. If you run an additional instance of the same application code, but with a different application name, the KCL treats the second instance as an entirely separate application that is also operating on the same stream.
+ The KCL creates a DynamoDB table with the application name and uses the table to maintain state information (such as checkpoints and worker-shard mapping) for the application. Each application has its own DynamoDB table. For more information, see [Use a lease table to track the shards processed by the KCL consumer application](shared-throughput-kcl-consumers.md#shared-throughput-kcl-consumers-leasetable).
### Set up credentials
You must make your AWS credentials available to one of the credential providers in the default credential providers chain. You can you use the `AWSCredentialsProvider` property to set a credentials provider. The [sample.properties](https://github.com/awslabs/amazon-kinesis-client-python/blob/master/samples/sample.properties) must make your credentials available to one of the credentials providers in the [default credential providers chain](https://docs.aws.amazon.com/sdk-for-java/latest/reference/com/amazonaws/auth/DefaultAWSCredentialsProviderChain.html). If you are running your consumer application on an EC2 instance, we recommend that you configure the instance with an IAM role. AWS credentials that reflect the permissions associated with this IAM role are made available to applications on the instance through its instance metadata. This is the most secure way to manage credentials for a consumer running on an EC2 instance.
The sample's properties file configures KCL to process a Kinesis data stream called "words" using the record processor supplied in `AmazonKinesisSampleConsumer.cs`.
# Develop a Kinesis Client Library consumer in Python
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can use the Kinesis Client Library (KCL) to build applications that process data from your Kinesis data streams. The Kinesis Client Library is available in multiple languages. This topic discusses Python.
The KCL is a Java library; support for languages other than Java is provided using a multi-language interface called the *MultiLangDaemon*. This daemon is Java-based and runs in the background when you are using a KCL language other than Java. Therefore, if you install the KCL for Python and write your consumer app entirely in Python, you still need Java installed on your system because of the MultiLangDaemon. Further, MultiLangDaemon has some default settings you may need to customize for your use case, for example, the AWS Region that it connects to. For more information about the MultiLangDaemon on GitHub, go to the [KCL MultiLangDaemon project](https://github.com/awslabs/amazon-kinesis-client/tree/v1.x/src/main/java/com/amazonaws/services/kinesis/multilang) page.
To download the Python KCL from GitHub, go to [Kinesis Client Library (Python)](https://github.com/awslabs/amazon-kinesis-client-python). To download sample code for a Python KCL consumer application, go to the [KCL for Python sample project](https://github.com/awslabs/amazon-kinesis-client-python/tree/master/samples) page on GitHub.
You must complete the following tasks when implementing a KCL consumer application in Python:
**Topics**
+ [Implement the RecordProcessor class methods](#kinesis-record-processor-implementation-interface-py)
+ [Modify the configuration properties](#kinesis-record-processor-initialization-py)
## Implement the RecordProcessor class methods
The `RecordProcess` class must extend the `RecordProcessorBase` to implement the following methods. The sample provides implementations that you can use as a starting point (see `sample_kclpy_app.py`).
```
def initialize(self, shard_id)
def process_records(self, records, checkpointer)
def shutdown(self, checkpointer, reason)
```
**initialize**
The KCL calls the `initialize` method when the record processor is instantiated, passing a specific shard ID as a parameter. This record processor processes only this shard, and typically, the reverse is also true (this shard is processed only by this record processor). However, your consumer should account for the possibility that a data record might be processed more than one time. This is because Kinesis Data Streams has *at least once* semantics, meaning that every data record from a shard is processed at least one time by a worker in your consumer. For more information about cases in which a particular shard may be processed by more than one worker, see [Use resharding, scaling, and parallel processing to change the number of shards](kinesis-record-processor-scaling.md).
```
def initialize(self, shard_id)
```
**process\$1records**
The KCL calls this method, passing a list of data record from the shard specified by the `initialize` method. The record processor that you implement processes the data in these records according to the semantics of your consumer. For example, the worker might perform a transformation on the data and then store the result in an Amazon Simple Storage Service (Amazon S3) bucket.
```
def process_records(self, records, checkpointer)
```
In addition to the data itself, the record also contains a sequence number and partition key. The worker can use these values when processing the data. For example, the worker could choose the S3 bucket in which to store the data based on the value of the partition key. The `record` dictionary exposes the following key-value pairs to access the record's data, sequence number, and partition key:
```
record.get('data')
record.get('sequenceNumber')
record.get('partitionKey')
```
Note that the data is Base64-encoded.
In the sample, the method `process_records` has code that shows how a worker can access the record's data, sequence number, and partition key.
Kinesis Data Streams requires the record processor to keep track of the records that have already been processed in a shard. The KCL takes care of this tracking for you by passing a `Checkpointer` object to `process_records`. The record processor calls the `checkpoint` method on this object to inform the KCL of how far it has progressed in processing the records in the shard. If the worker fails, the KCL uses this information to restart the processing of the shard at the last known processed record.
For a split or merge operation, the KCL doesn't start processing the new shards until the processors for the original shards have called `checkpoint` to signal that all processing on the original shards is complete.
If you don't pass a parameter, the KCL assumes that the call to `checkpoint` means that all records have been processed, up to the last record that was passed to the record processor. Therefore, the record processor should call `checkpoint` only after it has processed all the records in the list that was passed to it. Record processors do not need to call `checkpoint` on each call to `process_records`. A processor could, for example, call `checkpoint` on every third call. You can optionally specify the exact sequence number of a record as a parameter to `checkpoint`. In this case, the KCL assumes that all records have been processed up to that record only.
In the sample, the private method `checkpoint` shows how to call the `Checkpointer.checkpoint` method using appropriate exception handling and retry logic.
The KCL relies on `process_records` to handle any exceptions that arise from processing the data records. If an exception is thrown from `process_records`, the KCL skips over the data records that were passed to `process_records` before the exception. That is, these records are not re-sent to the record processor that threw the exception or to any other record processor in the consumer.
**shutdown**
The KCL calls the `shutdown` method either when processing ends (the shutdown reason is `TERMINATE`) or the worker is no longer responding (the shutdown `reason` is `ZOMBIE`).
```
def shutdown(self, checkpointer, reason)
```
Processing ends when the record processor does not receive any further records from the shard, because either the shard was split or merged, or the stream was deleted.
The KCL also passes a `Checkpointer` object to `shutdown`. If the shutdown `reason` is `TERMINATE`, the record processor should finish processing any data records, and then call the `checkpoint` method on this interface.
## Modify the configuration properties
The sample provides default values for the configuration properties. You can override any of these properties with your own values (see `sample.properties`).
### Application name
The KCL requires an application name that is unique among your applications, and among Amazon DynamoDB tables in the same Region. It uses the application name configuration value in the following ways:
+ All workers that are associated with this application name are assumed to be working together on the same stream. These workers can be distributed on multiple instances. If you run an additional instance of the same application code, but with a different application name, the KCL treats the second instance as an entirely separate application that is also operating on the same stream.
+ The KCL creates a DynamoDB table with the application name and uses the table to maintain state information (such as checkpoints and worker-shard mapping) for the application. Each application has its own DynamoDB table. For more information, see [Use a lease table to track the shards processed by the KCL consumer application](shared-throughput-kcl-consumers.md#shared-throughput-kcl-consumers-leasetable).
### Set up credentials
You must make your AWS credentials available to one of the credential providers in the default credential providers chain. You can you use the `AWSCredentialsProvider` property to set a credentials provider. The [sample.properties](https://github.com/awslabs/amazon-kinesis-client-python/blob/master/samples/sample.properties) must make your credentials available to one of the credentials providers in the [default credential providers chain](https://docs.aws.amazon.com/sdk-for-java/latest/reference/com/amazonaws/auth/DefaultAWSCredentialsProviderChain.html). If you are running your consumer application on an Amazon EC2 instance, we recommend that you configure the instance with an IAM role. AWS credentials that reflect the permissions associated with this IAM role are made available to applications on the instance through its instance metadata. This is the most secure way to manage credentials for a consumer application running on an EC2 instance.
The sample's properties file configures KCL to process a Kinesis data stream called "words" using the record processor supplied in `sample_kclpy_app.py`.
# Develop a Kinesis Client Library consumer in Ruby
**Important**
Amazon Kinesis Client Library (KCL) versions 1.x and 2.x are outdated. KCL 1.x will reach end-of-support on January 30, 2026. We **strongly recommend** that you migrate your KCL applications using version 1.x to the latest KCL version before January 30, 2026. To find the latest KCL version, see [Amazon Kinesis Client Library page on GitHub](https://github.com/awslabs/amazon-kinesis-client). For information about the latest KCL versions, see [Use Kinesis Client Library](kcl.md). For information about migrating from KCL 1.x to KCL 3.x, see [Migrating from KCL 1.x to KCL 3.x](kcl-migration-1-3.md).
You can use the Kinesis Client Library (KCL) to build applications that process data from your Kinesis data streams. The Kinesis Client Library is available in multiple languages. This topic discusses Ruby.
The KCL is a Java library; support for languages other than Java is provided using a multi-language interface called the *MultiLangDaemon*. This daemon is Java-based and runs in the background when you are using a KCL language other than Java. Therefore, if you install the KCL for Ruby and write your consumer app entirely in Ruby, you still need Java installed on your system because of the MultiLangDaemon. Further, MultiLangDaemon has some default settings you may need to customize for your use case, for example, the AWS Region that it connects to. For more information about the MultiLangDaemon on GitHub, go to the [KCL MultiLangDaemon project](https://github.com/awslabs/amazon-kinesis-client/tree/v1.x/src/main/java/com/amazonaws/services/kinesis/multilang) page.
To download the Ruby KCL from GitHub, go to [Kinesis Client Library (Ruby)](https://github.com/awslabs/amazon-kinesis-client-ruby). To download sample code for a Ruby KCL consumer application, go to the [KCL for Ruby sample project](https://github.com/awslabs/amazon-kinesis-client-ruby/tree/master/samples) page on GitHub.
For more information about the KCL Ruby support library, see [KCL Ruby Gems Documentation](http://www.rubydoc.info/gems/aws-kclrb).