How to choose a decoupling service that suits your use case? In this article we’ll take you though some comparisons between AWS services – Kinesis vs SNS vs SQS – that allow you to decouple sending and receiving data. We’ll show you examples using Python to help you choose a decoupling service that suits your use case. Decoupling offers a myriad of advantages, but choosing the right tool for the job may be challenging. AWS alone provides several services that allow us to decouple sending and receiving data. While on the surface those services seem to provide similar functionality, they are designed for different use cases and each of them can be useful if applied properly to the problem at hand. AWS SQS As one of the oldest services at AWS, SQS has a track record of providing an extremely simple and effective decoupling mechanism. The entire service is based on and allowing for applications ( ) to poll for messages and process them. The message stays in the queue until some application picks it up, processes it, and deletes the message when it’s done. sending messages to the queue ex. ECS containers, Lambda functions The most important distinction between SQS and other decoupling services is that it’s NOT a publish-subscribe service. SQS has no concept of producers, consumers, topics, or subscribers. All it does is to provide a distributed queue that allows: sending messages to the queue, polling for messages being in the queue, picking up the messages from the queue, deleting a message from the queue once the message has been successfully processed. SQS does messages to any applications. Instead, once a message is sent to SQS, an application must for messages to receive and process them. Also, it’s not enough to pick up the message from the queue to make it disappear — the message stays in the queue until: not push actively poll it has been successfully processed and from the queue, removed the has — imagine that one containerized application picked up a message but while processing it, it got stuck in a zombie process. To ensure that this message will be processed, it becomes visible to other workers once the visibility timeout expires. This timeout can be set from 0 seconds up to 12 hours with the default being 30 seconds. visibility timeout expired The code snippet below demonstrates how you can: create a queue, send a message to the queue, receive, process, and delete a message. Here is a showing the same code as below. link to a Github gist Example showing SQS usage in Python — image by the author By default, SQS does not guarantee that the messages will be processed in the same order they were sent to the queue unless you choose the FIFO queue. This can be easily configured when creating a queue. sqs.create_queue( =queue_name, QueueName ={‘VisibilityTimeout’: ‘3600’, ‘FifoQueue’: ‘true’}) Attributes SNS Even though SNS stands for Simple Notification Service, it provides much more functionality than just the ability to send push notifications ( ). emails, SMS, and mobile push In fact, it’s a serverless allowing to send events to multiple applications ( ) at the same time ( ), including SQS queues, Lambda functions, Kinesis Data Streams, and generic HTTP endpoints. publish-subscribe messaging system subscribers fan-out In order to use the service, we only need to: create a topic, subscribe to a topic, confirm the subscription, start sending events to a topic to deliver them to all subscribers ( ). potentially multiple applications and people Anytime multiple services need to receive the same event, you should consider SNS rather than SQS. A message from an SQS queue can only be successfully processed by a single worker node or process. How to decide whether you need to use SQS vs. SNS? Therefore, if you need a fan-out mechanism, you need to create an SNS topic and implement queues for all applications that need to receive the specific event or data. Multiple queues can then subscribe to this SNS topic and receive the messages simultaneously. For instance, imagine a scenario as simple as having the possibility to publish the same event ( ) to both the development ( ) and production environment: message staging Using SNS to implement a fan-out mechanism allowing to distinguish between DEV and PROD resources — image by the author Again, that demonstrates how to: here is a simple Python script create an SNS topic, subscribe to an SNS topic, publish messages to an SNS topic. Example showing SNS usage in Python — image by the author AWS Kinesis Data Streams AWS provides an entire suite of services under the Kinesis family. When people say Kinesis, they typically refer to — a service allowing to process large amounts of streaming data in by leveraging and operating on of . Kinesis Data Streams near real-time producers consumers shards data records are scripts generated by Kinesis agents, producer libraries, or AWS SDKs which send data to the . Producers data stream are client libraries or AWS services ( ) which process data from those . Consumers AWS Lambda, Kinesis Data Firehose, Kinesis Data Analytics data streams Each consists of one or multiple . data stream shards A is a collection of that are uniquely identified by a sequence number. shard data records Each has a to determine which will store a specific . This should help to group data records commonly accessed together into the same shard. data record partition key shard data record Each also has a that holds the actual data. This data can be stored in various forms as long as it fits into a 1 MB blob object. data record data blob Once a is sent to the , it can stay there for a specified retention period from 24 hours to 7 days. data record data stream Apart from Kinesis Data streams, the “Kinesis family” includes: — a service that automatically delivers data records into S3, Redshift, service providers like Datadog, New Relic, MongoDB, or Splunk, and to other sources via generic HTTP endpoints. The caveat behind this service is that it does not deliver data in real-time data, but rather as micro-batches. Data gets delivered to the chosen destination either on a 60–900 seconds cadence or after the predefined buffer size (1–128 MB) gets filled up. Kinesis Data Firehose — a service that allows us to transform and analyze data as it comes into the stream. We can use a SQL-like interface to do transformations ( ) and gather insights by aggregating streaming data into timely buckets ( ) by means of a sliding window aggregation. Kinesis Data Analytics ex. use regex to parse information from JSON or streamed logs ex. 15-minutes buckets A simple demo of Kinesis Data Streams To demonstrate how Kinesis Data Streams can be used, we will request the current cryptocurrency market prices ( ) and ingest them into a Kinesis . data producer data stream To create a data stream in the AWS console, we need to provide a stream name and configure the number of shards: Create a data stream— image by the author Then, we can start sending live market prices into the stream. In the example below, we send them every 10 seconds. with the same code. Here is a link to a Github gist Example showing Kinesis Data Streams usage in Python — image by the author The script will run indefinitely until we manually stop it. Using Kinesis Data Firehose as a data consumer So far, we configured a Kinesis data producer, sending real-time market prices to the data stream. There are many ways to implement a Kinesis consumer — for this demo, we’ll implement the simplest method which is to leverage a Firehose delivery stream. We can configure to send data to S3 directly in the AWS console. We need to select our previously created data stream and for everything else, we can apply the defaults. Kinesis Data Firehose Create a delivery stream — image by the author The most important part is to configure the destination — in our use case, we choose S3 and select a specific bucket: Create a delivery stream — image by the author We need to configure how frequently the micro-batches of data should be sent to S3: Create a delivery stream — image by the author We can then confirm to create a delivery stream: Create a delivery stream — image by the author Shortly after the delivery stream’s creation, we should be able to see new data arriving every minute in our S3 bucket: Data from a delivery stream in S3 — image by the author To see how this data looks like, we can download one file from S3 and inspect its content: Data from the delivery stream — image by the author How to monitor the health of the data streams? Even though Kinesis Data Streams is serverless, it requires proper allocation of data across shards. One possible way to track any write throttles is to use Dashbird. In the image below, we can see how many records are sent to the stream each minute. It shows us that we don’t always receive exactly 10 records per minute. Kinesis Data Streams in — image by the author Dashbird allows you to configure alerts on write throttles: Dashbird Alerts for Kinesis Data Streams in Dashbird — image by the author This is how the alert could look like if triggered: Alerts for Kinesis Data Streams in Dashbird — image by the author Which service should you choose for your use case? Among the three services from the title, Kinesis is the most difficult one to use and operate at scale. It’s best to start with an SNS topic and one or more SQS queues subscribed to it. Kinesis shines when you need to perform map-reduce-like operations on streaming data, as it allows you to aggregate similar records and build real-time analytical applications. At the same time, monitoring shards and Kinesis stream throughput adds some additional complexity and increases the error space where something can go wrong. If your only argument for Kinesis Data Streams is the ability to replay data, you could achieve the same by introducing a Lambda function that subscribes to the SNS topic and loads all received messages to some database such as DynamoDB or Aurora. By leveraging a timestamp of data insertion, you would know exactly when a specific message was received which simplifies debugging in case of errors. To make it easier to choose a decoupling service for your use case, I created a table comparing features and characteristics of those three services. SNS vs. SQS vs. Kinesis Data Streams — image by the author Conclusion In this article, we looked at the differences between SNS, SQS, and Kinesis Data Streams. We’ve built a simple demo showing how to send data to Kinesis from data producers, how a delivery stream can consume the data, and how to monitor any potential write throttles. For each service, we demonstrated how it can be used in Python and concluded with a table comparing the service characteristics. References and further reading: Triggering AWS Lambda with SNS 6 Common Pitfalls of AWS Lambda with Kinesis Trigger Amazon Kinesis Data Streams Terminology and Concepts Why should I use Amazon Kinesis and not SNS-SQS? Previously published at https://dashbird.io/blog/kinesis-sqs-sns-comparison/

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