A Visual Introduction to Apache Kafka

Paul Brebner
Technology Evangelist
www.instaclustr.com
sales@instaclustr.com
© Instaclustr Pty Limited, 2022 [https://www.instaclustr.com/
company/policies/terms-conditions/]. Except as permitted by the
copyright law applicable to you, you may not reproduce, distribute,
publish, display, communicate or transmit any of the content of this
document, in any form, but any means, without the prior written
permission of Instaclustr Pty Limited.

In this Visual Introduction to Kafka,
we’re going to build a
Postal
Service
We’ll learn about Kafka Producers,
Consumers, Topics, Partitions, Keys,
Records, Delivery Semantics
(Guaranteed delivery, and who gets what
messages), Consumer Groups, Kafka
Connect and Streams!
©Instaclustr Pty Limited 2019, 2021, 2022

Kafka is a distributed streams processing system, it
allows distributed producers to send messages to
distributed consumers via a Kafka cluster.
What is
Kafka?

Kafka has lots of benefits:
It’s Fast: It has high throughput and low latency
It’s Scalable: It’s horizontally scalable, to scale just add nodes and partitions
It’s Reliable: It’s distributed and fault tolerant
It has Zero Data Loss: Messages are persisted to disk with an immutable log
It’s Open Source: An Apache project
And it’s available as an Instaclustr Managed Service: On multiple cloud platforms
Managed
Service
Fast
Scalable
Reliable
Durable
Open Source

But the usual
Kafka diagram
(right) is a bit
monochrome
and boring.

This visual introduction
will be more
colourful
and it’s going to be
an extended story…

Let’s build a modern day fully electronic postal service
T
o send messages from A to B
Postal
Service
A B

T
o B, the consumer,
the recipient of the
message.
A is a producer,
it sends a message…
First, we need an “A”.

Due to the decline in
“snail mail” volumes,
direct deliveries have
been canceled.
CANCELED
Actually,
not.

Consumers poll for messages by
visiting the counter at the post
office.
Poste Restante is not a post office
in a restaurant, it’s called general
delivery (in the US).
The mail is delivered to a post
office, and they hold it for you
until you call for it.
Instead we have
“Poste Restante”
Image: La Poste Restante, Francois-Auguste Biard (Wikimedia)

Disconnected delivery—consumer doesn’t need to be
available to receive messages
There’s less effort for the messaging service— only
has to deliver to a few locations not many consumer
addresses
And it can scale better and handle more
complex delivery semantics! Postal
Service
Kafka topics act like a Post Office.
What are the benefits?

Kafka Topics have 1 or more Partitions. Partitions function like multiple counters
and enable high concurrency.
A single counter introduces
delays and limits concurrency.
More counters
increases concurrency and
reduces delays.
First lets see how it scales.
What if there are many consumers for a topic?

Santa
North
Pole
Let’s see what a message looks like.
In Kafka a message is
called a Record and is a
bit like a letter.
The topic is the
destination,
The North Pole.

Santa
North
Pole Time semantics are flexible,
either the time of event
creation, ingestion, or
processing.
timestamp,
offset,
partition
T
opic
The “Postmark” includes a
timestamp, offset in the
topic, and the partition it
was sent to.

Santa
North
Pole
We want this letter
sent to Santa not
just a random Elf.
timestamp,
offset,
partition
T
opic
Key Partition
(optional)
There’s also a thing called a Key, which is
optional. It refines the destination so it’s a
bit like the rest of the address.

Santa
North
Pole
And the value is the contents (just a byte array).
Kafka Producers and consumers need to have a shared
serializer and de-serializer for both the key and value.
timestamp,
offset,
partition
T
opic
Key Partition
(optional)
Value (Content)

Kafka doesn’t look
inside the value, but
the Producer and
Consumer do, and the
Consumer can try and
make sense of the
message
(Can you?!)
Image: Dear Santa by Zack Poitras / http://theinclusive.net/article.php?id=268

let’s look at
delivery semantics
For example, do we care if the
message actually arrives or not?
Next

Last century, homing pigeons were
prone to getting lost or eaten by
predators, so the same message was
sent with several pigeons.
Yes we do!
Guaranteed
message
delivery is
desirable.

How does Kafka guarantee delivery?
The message is always
persisted to disk.
This makes it
resilient to
power failure
A Message (M1) is
written to a broker (2).
Producer
M1
M1
Broker
1
Broker
2
Broker
3

Producer
Broker
1
Broker Broker
3
M1 M1 M1
The message is also replicated on
multiple brokers, 3 is typical.
2

Producer
M1
M1 M1
And makes it resilient to
loss of some servers
(all but one).
Broker
1

Finally the producer gets acknowledgement once the message is
persisted and replicated (configurable for number, and sync or async).
Producer
M1
Broker
1
Broker
2
Broker
3
M1 M1
Acknowledgement
This also increases the
read concurrency as
partitions are spread
over multiple brokers.
The message is now
available from more
than one broker in
case some fail.

let’s look at another aspect of
delivery semantics
Who gets the messages and how many
times are messages delivered?
Now

Producer
Consumer
Consumer
Consumer
Consumer
?
Kafka is “pub-sub”. It’s loosely coupled,
producers and consumers don’t know about
each other.

Filtering, or which consumers get which messages, is topic based.
- Producers send messages to topics.
- Consumers subscribe to topics of interest, e.g. parties.
- When they poll they only receive messages sent to those topics.
None of these consumers will receive messages sent to the “Work” topic.
Producer
Consumer
Consumer
Consumer
Consumer
Topic “Parties”
Topic “Work”
Consumers subscribed
to Topic “Parties”
Consumers poll to
receive messages
from “Parties”
Consumers not subscribed to
“Work” messages

A few more details and we can see how this works.
Kafka works like Amish Barn raising.
Partitions and a consumer group share work
across multiple consumers, the more
partitions a topic has the more consumers
it supports.
Image: Paul Cyr ©2018 NorthernMainePhotos.com

Kafka also works like Clones.
It supports delivery of the same message to
multiple consumers with consumer groups.
Kafka doesn’t throw messages away
immediately they are delivered, so the
same message can be delivered to
multiple consumer groups.
Image: Shutterstock.com

Consumers subscribed to ”parties” topic are allocated partitions.
When they poll they will only get messages from their allocated
partitions.
Consumer
Partition n
Topic “Parties”
Partition 1
Producer
Partition 2
Consumer Group
Consumer
Consumer Group
Consumer
Consumer

This enables consumers in the same group to share the work
around. Each consumer gets only a subset of the available
messages.
Partition n
Topic “Parties”
Partition 1
Producer
Partition 2
Consumer Group
Consumer
Consumer
Consumers share
work within groups
Consumer

Multiple groups enable message broadcasting. Messages
are duplicated across groups, as each consumer group
receives a copy of each message.
Consumer
Consumer
Consumer
Consumer
Topic “Parties”
Partition 1
Partition 2
Partition n
Producer
Consumer Group
Consumer Group
Messages are
duplicated across
Consumer groups

Which messages are delivered to which consumers?
The final aspect of delivery semantics
is to do with message keys.
If a message has a key, then Kafka uses
Partition based delivery.
Messages with
the same key are
always sent to the same partition and
therefore the same consumer. And the
order (within partitions) is guaranteed.
Key

But if the key is null, then Kafka uses
round robin delivery.
Each message is delivered to the next partition.
Round
robin
delivery

Let’s look at a concrete example with two consumer groups:
Group 1: Nerds
which has multiple consumers
Group 2: The Pugsters
which has a single consumer, Zug
Bill
Paul
Penny
Kate
Millie
Jenny
Image: Nenad Aksic / Shutterstock.com

Consumer 1
(Bill)
Consumer 2
(Jenny)
Consumer 1 (Zug
from The Pugsters)
Topic “Parties”
Partition 1
Partition 2
Partition n
Producer
Group “Nerds”
Group “Pugsters”
Consumers
subscribe to
“Parties”
Each message (1, 2, etc.) is sent to the next
partition, and consumers allocated to that
partition will receive the message when they
poll next.
Looking at the case
where there’s
No Keyfirst
Round robin
No
Key
1
2
etc
1
2
1
2
Consumer n

Here’s what actually happens.
We’re not showing the producer,
topics, or partitions for simplicity.
You’ll have to imagine them.
Bill
Paul
Penny
Kate
Millie
Jenny
No
Key

Bill
Penny
Kate
Millie
Jenny
Both Groups subscribe to T
opic“parties”
(assuming 6 partitions, each consumer in the Nerds
group gets 1 partition each; Zug gets them all)
1
Paul
Subscribe to
“Parties”
No
Key

Bill
Pau
l
Penny
Kate
Millie
Jenny
Producer sends record with the
value “Pool party—Invitation” to
“parties” topic (there’s no key)
2
Invitation
No
Key
Value

Bill
Paul
Penny
Kate
Millie
Jenny
Bill and Zug receive a copy of the
invitation and plan to attend
3
Invitation Invitation
No
Key

Bill
Pen ny
Pau
l
Kate
Millie
Jenny
The Producer sends another record with the
value “Pool party—Canceled”
4
No
Key
Invitation
Canceled
Invitation

Bill
Paul
Penny
Kate
Millie
Jenny
In the Nerds group, Jenny gets the message this time as it’s round robin, and Zug
gets it as he’s the only consumer in his group:
▶ Jenny ignores it as she didn’t get the original invite
▶ Bill wastes his time trying to go (as he doesn’t know it’s canceled)
▶ The rest of the gang aren’t surprised at not receiving any invites and
stay home to do some hacking
5
Invitation
Canceled
No
Key
Invitation
Canceled

Zug plans
something else
fun instead… A
jam session with
his band

Consumer 1
(Bill)
Consumer 2
(Jenny)
Consumer 1
(Zug)
Topic “Parties”
Partition 1
Partition 2
Partition n
Producer
Group “Nerds”
Group “Pugster”
Consumers
subscribe to
“Parties”
The key is hashed to a partition, so the Message is
always sent to that partition. Assume there are 3
messages, and messages 1 and 2 are hashed to the
same partition.
How does it work if
there is a Key?
1,2
3
etc
1,2
3
1,2
3
Consumer n
Hashed to
partition Key

Bill
Paul
Penny
Kate
Millie
Jenny
As before Both Groups subscribe to
Topic “parties”
The Producer sends a record with the
key equal to “Pool Party” and the
value equal to “Invitation” to
“parties” topic
Here’s what happens with a
key, assuming that the key is
the “title” of the message
(“Pool Party”), and the value
is invitation or canceled
1
2
Key
Invitation
Key
Value

Bill
Paul
Penny
Kate
Millie
Jenny
As before, Bill and Zug receive a copy of the
invitation and plan to attend
3
Invitation
Key
Key
Invitation
Key
Value
Value

Bill
Pen n
y
Kate
Millie
Jenny
The Producer sends another record with
the same key but with the value
“canceled” to “parties” topic
4
Key
Invitation
Key
Value
Canceled
Paul
Value
Key
Invitation
Key
Value

Paul
Penny
Kate
Millie
Jenny
This time, Bill and Zug receive the cancelation
(the same consumers as the key is identical)
5
BK
il
el
y
Key
Value
Invitation
Key
Value
Bill
Canceled
Key
Value
Key
Invitation
BK
il
el
y
Key
Canceled
Key
Value
Key

Paul
Penny
Kate
Millie
The Producer sends out another
invitation to a Halloween party.
The key is different this time.
6
Key
Key
Jenny
Bill

Paul
Penny
Kate
Millie
Jenny
Jenny receives the Halloween invitation as the key is
different and the record is sent to Jenny’s partition.
Zug is the only consumer in his group so he gets
every record no matter what partition it’s sent to.
7
Key
Bill
Jenny’s
partitionkey

This time Zug
gets dressed up
and has fun at
the party.

But wait! There’s more—
event reprocessing
(time travel)!
Kafka stores message streams on disk, so
Consumers can go back and request the same
messages they’ve already received, earlier messages, or
ignore some messages etc.

So Zug can go
“back to the
future”!

But! The postal system
is global and
heterogeneous

How can
post offices
be connected?

Underground pneumatic tubes delivered mail between
postal facilities in USA cities in the 1900’s
(Source: Wikimediacommons)
Compressed Air?

Sink
Source
Kafka Connect enables message flows across
heterogenous systems.
From Sources to Sinks via a Lake (Kafka)

Kafka Connect Architecture:
Source and Sink Connectors

Form Pipelines (Berlin)
(Source: Paul Brebner)

For Beer?
(Source: Paul Brebner)

Tides Topic
REST call
JSON result
{"metadata": {
"id":"8724580",
"name":"Key West",
"lat":"24.5508”,
"lon":"-81.8081"},
"data":[{
"t":"2020-09-24 04:18",
"v":"0.597"}]}
Elasticsearch sink connector Tides Index
Example of a Kafka Connect IoT pipeline:
Tidal Data à Kafka à Elasticsearch à Kibana
©Instaclustr Pty Limited, 2021
REST source connector
{"metadata": {
"id":"8724580",
"name":"Key West",
"lat":"24.5508”,
"lon":"-81.8081"},
"data":[{
"t":"2020-09-24
04:18",
"v":"0.597"}]}

Tides Topic
REST call
JSON result
{"metadata": {
"id":"8724580",
"name":"Key West",
"lat":"24.5508”,
"lon":"-81.8081"},
"data":[{
"t":"2020-09-24 04:18",
"v":"0.597"}]}
Elasticsearch sink connector Tides Index
Example of a Kafka Connect IoT pipeline:
Tidal Data à Kafka à Elasticsearch à Kibana
©Instaclustr Pty Limited, 2021
REST source connector
{"metadata": {
"id":"8724580",
"name":"Key West",
"lat":"24.5508”,
"lon":"-81.8081"},
"data":[{
"t":"2020-09-24
04:18",
"v":"0.597"}]}
Connectors
require
Configuration

Source: https://commons.wikimedia.org/wiki/File:Royal_mail_sorting.jpg
What’s Still Missing?
Mail Sorting

Automated!
Source: https://commons.wikimedia.org/wiki/File:Post_Sorting_Machine_(4479045801).jpg

At Scale!
(Source: https://commons.wikimedia.org/w/index.php?search=mail+sorting&title=Special:MediaSearch&go=Go&type=image)

Kafka Streams:
Topics in, Topics out, via Streams
All Kafka APIs: Producer, Consumer, Connect, Streams

(Source: Shutterstock)
Simple Streams Topology

Join
Group
Filter
Aggregate
etc.
Complex Streams Topology

Kafka Streams = Rapids!?

Streams get complicated quickly!
One way to keep dry…

Or, This Diagram Which Explains
The Order of Streams DSL Operations
(Source: https://kafka.apache.org/20/documentation/streams/developer-guide/dsl-api.html)

Dr Black has been murdered in the
Billiard Room with a Candlestick!
Whodunnit?!
[KSTREAM-FILTER-0000000024]: Conservatory: Professor Plum has no alibi
[KSTREAM-FILTER-0000000024]: Library: Colonel Mustard has no alibi
[KSTREAM-FILTER-0000000024]: Billiard Room: Mrs White has no alibi
Cluedo Kafka Streams Example
Tracks who’s in
what rooms and
when, and emits
list of suspects
without an alibi

Topology of Cluedo Streams Example
This tool is very useful for
visualizing and debugging streams
https://zz85.github.io/kafka-streams-viz/

Some Kafka Use Cases

Example 1 - Kafka ”Kongo” Logistics IoT
Application – Goods, Warehouses, Trucks,
Sensors and Rules

Detect transportation and storage violations in
real-time

And Kafka Streams to prevent Truck Overloading

Example 2 - One of these things is not
like the others

Massively Scalable Anomaly
Detection with Kafka and Cassandra

19 Billion Checks/day with 470 CPU Cores
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250 300 350 400 450 500
Billion
checks/day
Total CPU Cores
Anomaly checks/day (billion)
19
Billion

Example 3 - Which Came First? State
or Events?
State
State
Events

Change Data Capture (CDC) with Debezium and
Kafka Connect
State to Events and back to State again
State
Events
State

Apache Kafka:
https://kafka.apache.org/
Gently down the Stream:
www.gentlydownthe.stream
That’s it for this
short visual
introduction to
Apache Kafka.
For more information
please have a look at the
Apache Kafka docs, the
Instaclustr Blogs, and check out
our free Kafka trial.
“Gently down the
Stream” - another
“Visual” introduction to
Kafka, with Otters!

All of my blogs (Cassandra, Kafka, MirrorMaker, Spark, Zookeeper,
OpenSearch, Redis, PostgreSQL, Debezium, Cadence, etc)
www.instaclustr.com/paul-brebner/
Kafka Streams Cluedo Example (part of “Kongo” Kafka intro series)
www.instaclustr.com/blog/kongo-5-3-apache-kafka-streams-examples/
Kafka Connect Pipeline Series (Tides data processing)
www.instaclustr.com/blog/kafka-connect-pipelines-conclusion-pipeline-series-part-10/
Kafka Xmas Tree Lights Simulation (my 1st Kafka program)
www.instaclustr.com/blog/seasons-greetings-instaclustr-kafka-christmas-tree-light-simulation/
Instaclustr’s Managed Kafka (Free Trial)
www.instaclustr.com/platform/managed-apache-kafka/
Instaclustr Blogs
© Instaclustr Pty Limited 2019, 2021, 2022 [https://www.instaclustr.com/company/policies/terms-conditions/]. Except as permitted by the copyright law applicable to you, you may not reproduce, distribute,
publish, display, communicate or transmit any of the content of this document, in any form, but any means, without the prior written permission of Instaclustr Pty Limited.

A Visual Introduction to Apache Kafka

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