Agfdhyk

I want to create a simple sensor data based application with apache kafka. My question is very simple and is referenced to the basic concept of apache kafka. I'm a beginner at apache kafka.

Here my requirement:

I get sensor data via an byte array with different data inside.
For example the array exists of three entries (Temperature 1, Temperature 2 and Voltage). Here one example with 4 arrays and value data. Each array comes in a defined timestamp.

Array 1: [ 1, 2, 3 ]

Array 2: [ 4, 5, 6 ]

Array 3: [ 7, 8, 9 ]

Array 4: [ 10, 11, 12 ]

Now I want to read these arrays and want to produce messages for three topics:

• topic-temp1




• topic-temp2




• topic-voltage

The order of producing is:

• Read array 1


• produce message to topic-temp1 (value=1)


• produce message to topic-temp2 (value=2)



• produce message to topic-voltage (value=3)




• Read array 2



• produce message to topic-temp1 (value=4)


• produce message to topic-temp2 (value=5)



• produce message to topic-voltage (value=6)




• Read array 3



• produce message to topic-temp1 (value=7)


• produce message to topic-temp2 (value=8)


• produce message to topic-voltage (value=9)

... Read array n ...

After that I have 3 Topics with different data inside:

• topic-temp1: 1, 4, 7, 10




• topic-temp2: 2, 5, 8, 11




• topic-voltage: 3, 6, 9, 12

Now to my question:
I want to create a software application that consumes these 3 topics. I want to display 3 graphs (temp1, temp2, voltage) in one diagram. The y-axe is the signal value and the x-axe is the timestamp.

How can I quarantee that I get the consumed values at the same timestamp? Only the I can overlay the graphs.

• 1,2,3




• 4,5,6




• 7,8,9




• 10,11,12

Should I use the Kafka-Stream API? One input-stream-topic (byte array) and three output-stream-topics? How to ensure that these three values are together produced and will be consumed together?

Or should I use a simple consumer api and access the data via offset value. because the offset should be the same for the entries (1,2,3) (4,5,6) ..., because I produced them in this order?

Thank you in advance!

I suggest you use one topic of sensor-resdings with a payload of sensor name (or preferably a UUID), so you know which sensor sent the data, and data it generates, as one whole message.

Otherwise, joining data purely by timestamp doesn't seem that fail proof.

Your message key can be the UUID/name, and you can scale that to hundreds of partitions

You could binary encode the data you're sending, but I will use a JSON string for illustration

{

 "sensor_id" : "some unique name", 

 "temperatures" [1,2],

 "voltage": 3

}

If you want three topics out of that, you can very easily create three output topics using Kafka Streams or KSQL

Else, go ahead and create individual topics, but add the ID/name so you can join on that, using windows of time on orders of seconds or minutes, not trying to adjust for lag where one event is just microseconds off and you cannot join messages