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By Colin McCabe
Building Microservices
with Apache Kafka™

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About Me

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Roadmap
● Example network service
• Why microservices?
• Why Kafka?
● Apache Kafka background
● How Kafka helps scale microservices
● Kafka APIs
• Kafka Connect API
• Kafka Streams API
● Wrap up
● New Kafka features and improvements

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Newsfeed Application

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Single Process
First Try: Monolithic Service

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Emailer
Second Try: Microservices with REST
HDFS
Connector
Metrics
Connector
Frontend

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Third Try: Microservices with Kafka
Frontend

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Themes
● Improving Decoupling
• Everything in one big app: no decoupling
• Microservices with REST: multiple services
• Microservices with Kafka: decoupled services sharing
data
● Improving Scalability
• Everything in one big app: single node
• Microservices with REST: one node per service
• Microservices with Kafka: scalable microservices

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Apache Kafka
● A distributed streaming platform
● https://kafka.apache.org/intro
● Kafka was built at LinkedIn around 2010
● Multi-platform: clients in Java, Scala, C, C++, Python, Go, C#, …

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Kafka Adoption

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Kafka Concepts: the 10,000 foot view
● 4 APIs
• Producer
• Consumer
• Connector
• Stream Processor

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Producers and Consumers
Producer
Consumer
Producer Producer
Consumer Consumer Consumer
write messages
read messages
message
● key
● value

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Topics
Frontend
{
‘story’: ‘my news story’,
‘user’: ‘foo’,
‘timestamp’: <time>
}
‘views’
topic
Backend

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Kafka is Durable
Frontend
● Data is
replicated to
multiple servers
and persisted to
disk.
● Configurable log
retention.
● Consumers can
read from any
part of the log.
‘views’
topic

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Scaling with Kafka
● Can have multiple producers writing to a topic
● Can have multiple consumers reading from a topic
● Can add new microservices to consume data easily
• Example: add more microservices processing views
• Organize microservices around data, rather than APIs
● Can add more Kafka brokers to handle more messages and
topics
• Horizontal scalability

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Scaling a Topic with Multiple Partitions
Frontend
events
topic
Backend Backend Backend

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Load Balancing with Multiple Consumers
Frontend
emailer consumer
group
story_emails topic

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Partition Reassignment
Frontend
emailer consumer
group
story_emails topic

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Connecting to External Services
Frontend
Kafka
Connect API

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Kafka Connect API
docs.confluent.io/current/connect/
Connector Instance
● Responsible for
copying data
between Kafka and
an external system
Connector Task
Connector Plugin

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Kafka Streams API
kafka.apache.org/
documentation/streams
● Process streams of data.
● Fault-tolerant and
scalable.

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Calculating News Reader Metrics
Alice 13
Bob 4
Chao 25
Bob 19
Dave 55
...
Alice
europe
Bob us
Chao asia
Bob us
Dave
europe
...
europe 68
us
23
asia 25
...
+ =
clicks locations clicks per location

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Kafka Streams API
● Inputs and outputs are
Kafka streams
● Fault-tolerance,
rebalancing, scalability
provided by Kafka
● KStream
● KTable

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Joining the Clicks and Location Streams in KStreams
KStream<String, Long> userClicksStream =
builder.stream(..., "user-clicks-topic");
KTable<String, String> userRegionsTable =
builder.table(..., "user-regions-topic")
KTable<String, Long> clicksPerRegion = userClicksStream
.leftJoin(userRegionsTable, (c, r) ->
new RegionWithClicks(r == null ? "UNKNOWN" : r, c))
.map((user, regionWithClicks) -> new
KeyValue<>(regionWithClicks.getRegion(),
regionWithClicks.getClicks())).
reduceByKey((c1, c2) -> c1 + c2, ...);
clicksPerRegion.to("clicks-per-region-topic", ...);

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Wrap-Up
Frontend
Kafka
Connect
Kafka
Streams
load
balancing &
scalability
decouple
front-end and
back-end

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New Kafka Features and Improvements
● Exactly once semantics in Kafka 0.11
• https://www.confluent.io/blog/exactly-once-semantics-
are-possible-heres-how-apache-kafka-does-it/
● Consumer and producer performance improvements
• Up to +20% producer throughput
• Up to +50% consumer throughput
● Better CLASSPATH isolation for Kafka Connect connectors

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Conclusion
● The loose coupling, deployability, and testability of
microservices makes them a great way to scale.
● Apache Kafka is an incredibly useful building block for many
different microservices.
● Kafka is reliable and does the heavy lifting
● Kafka Connect is a great API for connecting with external
databases, Hadoop clusters, and other external systems.
● Kafka Streams can process data in realtime.
● https://www.confluent.io/solutions/microservices/

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Thank You!
https://www.confluent.io/download
https://www.confluent.io/careers