Testing Kafka Streams Applications

Yeva Byzek continues her series on testing Kafka-based streaming applications:

When you create a stream processing application with Kafka’s Streams API, you create a Topologyeither using the StreamsBuilder DSL or the low-level Processor API. Normally, the topology runs with the KafkaStreams class, which connects to a Kafka cluster and begins processing when you call start(). For testing though, connecting to a running Kafka cluster and making sure to clean up state between tests adds a lot of complexity and time.

Instead, developers can unit test their Kafka Streams applications with utilities provided by kafka-streams-test-utils. Introduced in KIP-247, this artifact was specifically created to help developers test their code, and it can be added into your continuous integration and continuous delivery (CI/CD) pipeline.

Streaming applications need tested just like any other.

Generating Test Data In Kafka

Yeva Byzek takes us through the Kafka Connect Datagen connector:

Short of using real data from a real source, you do have a few options on how to generate more interesting test data for your topics. One option is to write your own client. Kafka has many programming language options—you choose: Java, Python, Go, .NET, Erlang, Rust—the list goes on. You can write your own Kafka client applications that produce any kind of records to a Kafka topic, and then you’re set.
But wouldn’t it be great if you could generate data locally to just fill topics with messages? Fortunately, you’re in luck! Because we have those data generators.

Click through for a demonstration.

KSQL Deployment Options

Hojjat Jafarpour shows us two deployment options for Kafka Streams with KSQL:

As I mentioned, we have implemented KSQL on top of the Kafka Streams API. This means that every KSQL query is compiled into a Kafka Streams application. Therefore, KSQL queries follow the same execution model of Kafka Streams applications.
A query can be executed on multiple instances, and each instance will process a portion of the input data from the input topic(s) as well as generate portions of the output data to output topic(s). Based on this execution model and depending on how we want to run our queries, currently, KSQL provides two deployment options.

Read on for those options.

Comparing Streaming Engines

George Vetticaden compares Spark Streaming, Storm, and Kafka Streams:

Before the addition of Kafka Streams support, HDP and HDF supported two stream processing engines:  Spark Structured Streaming and Streaming Analytics Manager (SAM) with Storm. So naturally, this begets the following question:
Why add a third stream processing engine to the platform?
With the choice of using Spark structured streaming or SAM with Storm support, customers had the choice to pick the right stream processing engine based on their non- functional requirements and use cases. However, neither of these engines addressed the following types of requirements that we saw from our customers:

And this doesn’t even include Samza or Flink, two other popular streaming engines.

My biased answer is, forget Storm.  If you have a legacy implementation of it, that’s fine, but I wouldn’t recommend new streaming implementations based off of it.  After that, you can compare the two competitors (as well as Samza and Flink) to see which fits your environment better.  I don’t think either of these has many scenarios where you completely regret going with, say, Kafka Streams instead of Spark Streaming.  Each has its advantages, but they’re not so radically different.

Using Databricks Delta In Lieu Of Lambda Architecture

Jose Mendes contrasts the Lambda architecture with the Databricks Delta architecture and gives us a quick example of using Databricks Delta:

The major problem of the Lambda architecture is that we have to build two separate pipelines, which can be very complex, and, ultimately, difficult to combine the processing of batch and real-time data, however, it is now possible to overcome such limitation if we have the possibility to change our approach.
Databricks Delta delivers a powerful transactional storage layer by harnessing the power of Apache Spark and Databricks File System (DBFS). It is a single data management tool that combines the scale of a data lake, the reliability and performance of a data warehouse, and the low latency of streaming in a single system. The core abstraction of Databricks Delta is an optimized Spark table that stores data as parquet files in DBFS and maintains a transaction log that tracks changes to the table.

It’s an interesting contrast and I recommend reading the whole thing.

Configuring Kafka Streams For Least Privilege

Gwen Shapira explains how we can assign minimal rights to Kafka Streams and KSQL users:

The principle of least privilege dictates that each user and application will have the minimal privileges required to do their job. When applied to Apache Kafka® and its Streams API, it usually means that each team and application will have read and write access only to a selected few relevant topics.

Organizations need to balance developer velocity and security, which means that each organization will likely have their own requirements and best practices for access control.

There are two simple patterns you can use to easily configure the right privileges for any Kafka Streams application—one provides tighter security, and the other is for more agile organizations. First, we’ll start with a bit of background on why configuring proper privileges for Kafka Streams applications was challenging in the past.

Read the whole thing; “granting everybody all rights” generally isn’t a good idea, no matter what your data platform of choice may be.

Apache Samza At 1.0

Jagadish Venkatraman announces Apache Samza 1.0:

We are pleased to announce today the release of Samza 1.0, a significant milestone in the history of the project. Apache Samza is a distributed stream processing framework that we developed at LinkedIn in 2013. Samza became a top-level Apache project in 2014. Fast-forward to 2018, and we currently have over 3,000 applications in production leveraging Samza at LinkedIn. The use-cases include detecting anomalies, combating fraud, monitoring performance, notifications, real-time analytics, and many more. Today, Samza integrates not only with Apache Kafka, but also with many other systems, including Azure EventHubsAmazon Kinesis, HDFS, ElasticSearch, and Brooklin. Multiple companies like Slack, TripAdvisor, eBay, and Optimizely have adopted Samza.

We view Samza 1.0 as a step towards our vision of making stream processing universally accessible. In this post, we describe our journey in building and scaling a distributed stream processing system. We also present the key features in Samza 1.0: a rich high-level API, event-time-based processing, integration with Apache Beam, Samza SQL, a standalone mode to run Samza without YARN, and a new test framework for Samza applications.

This runs in the same space as Spark Streaming, Flink, and Kafka Streams, so there are plenty of competitors and a lot of innovation.

Spark Streaming On Azure Databricks

Tristan Robinson shows us how to run Spark Streaming within Azure Databricks:

Real-time stream processing is becoming more prevalent on modern day data platforms, and with a myriad of processing technologies out there, where do you begin? Stream processing involves the consumption of messages from either queue/files, doing some processing in the middle (querying, filtering, aggregation) and then forwarding the result to a sink – all with a minimal latency. This is in direct contrast to batch processing which usually occurs on an hourly or daily basis. Often is this the case, both of these will need to be combined to create a new data set.

In terms of options for real-time stream processing on Azure you have the following:

  • Azure Stream Analytics

  • Spark Streaming / Storm on HDInsight

  • Spark Streaming on Databricks

  • Azure Functions

Click through for more.

Monitoring Apache NiFi With A Custom Dashboard

Tim Spann has started a new series on monitoring Apache NiFi:

In this little proof of concept work, we grab some of these flows process them in Apache NiFi and then store them in Apache Hive 3 tables for analytics. We should probably push the data to HBase for aggregates and Druid for time series. We will see as this expands.

There are also other data access options including the NiFi REST API and the NiFi Python APIs.

Boostrap Notifier

  • Send notification when the NiFi starts, stops or died unexpectedly
  • Two OOTB notifications
  • Email notification service
  • HTTP notification service
  • It’s easy to write a custom notification service

Reporting Tasks

  • AmbariReportingTask (global, per process group)

  • MonitorDiskUsage(Flowfile, content, provenance repositories)

  • MonitorMemory

Much of this is an overview of the tools and measures available.

Troubleshooting KSQL Executions

Robin Moffatt shows us some of the tools available for researching problems with KSQL queries executed against a server:

What does any self-respecting application need? Metrics! We need to know how many messages have been processed, when the last message was processed and so on.

The simplest option for gathering these metrics comes from within KSQL itself, using the same DESCRIBE EXTENDED command that we saw before:

ksql> DESCRIBE EXTENDED GOOD_RATINGS;
[...]
Local runtime statistics
------------------------
messages-per-sec:      1.10 total-messages:     2898 last-message: 9/17/18 1:48:47 PM UTC failed-messages:         0 failed-messages-per-sec:         0 last-failed: n/a
(Statistics of the local KSQL server interaction with the Kafka topic GOOD_RATINGS)
ksql>

You can get more details, including explain plans, from this.  There are external tools which Robin demonstrates as well, which let you track the streams over time.

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