README.md

Kafka Schema registry poc

• Schema stored external (not in kafka)
• Reduce message size (messages serialized)
• If schema registry not available, breaks everything (critical component)

How to run

Two options (docker ONLY) :

1. Run docker with image: landoop/fast-data-dev
   docker-compose -f docker-compose.landoop up -d
   Image contains Kafka, Zookeeper, Schema Registry, Kafka-Connect, Landoop Tools, 20+ connectors.
   SchemaRegistry node provide RESTapi and stores all schemas versions.
   NB! To up container from this image, takes aprox. 1-3 mins.

2. Plain kafka, schema registry, zookeeper and proxy
   docker-compose -f docker-compose.confluent.yml up -d

Schema evolution at work

Run docker compose before these steps:

1. ./mvnw clean install
2. Execute KafkaAvroProducerV1 to produce message with V1
3. Execute KafkaAvroProducerV2 to produce message with V2
4. Try different consumers to consume messages with different versions

Data types

Primitive types

Type	Description
null	no value
boolean	binary value
int	32-bit
long	64-bit
float	floating-point 32-bit precision
double	floating-point 64-bit precision
bytes	seq of 8-bit
string	unicode char seq

Complex types

Type	Example
Enum	{"type":"enum","name":"Status","symbols":["CREATED","UPDATED"]}
Array	{"type":"array","items":"string"}
Map	{"type":"map", "values":"string"}
Union	{"name":"childs", "type":["null", "int"], "default":null}
Other Schema as a type	{"name":"employee", "type":"Employee"}

How to create schema

1. In code

  Schema.Parser parser = new Schema.Parser();
  Schema schema = parser.parse("{\n"
    + "   \"type\": \"record\",\n"
    + "   \"namespace\": \"no.sysco.middleware.poc.kafkaschemaregistry.avro\",\n"
    + "   \"name\": \"Business\",\n"
    + "   \"version\": \"1\",\n"
    + "   \"doc\":\"Business record contains name of company and list of customers\",\n"
    + "   \"fields\": [\n"
    + "     { \"name\": \"company_name\", \"type\": \"string\", \"doc\": \"Name of company\" },\n"
    + "     {\n"
    + "        \"name\": \"customers\",\n"
    + "        \"doc\": \"List of customers\",\n"
    + "        \"type\": {\n"
    + "          \"type\": \"array\",\n"
    + "          \"items\": {\n"
    + "            \"type\": \"record\",\n"
    + "            \"name\":\"Customer\",\n"
    + "            \"fields\":[\n"
    + "              { \"name\": \"first_name\", \"type\": \"string\", \"doc\":\"Customer name\" },\n"
    + "              { \"name\": \"last_name\", \"type\": \"string\", \"doc\": \"Customer last name\" }\n"
    + "            ]\n"
    + "          }\n"
    + "        }\n"
    + "     }\n"
    + "   ]\n"
    + "}");

2. Reflection - from POJO

  Schema schema = ReflectData.get().getSchema(Business.class);

Business class

public class Business {
    private String companyName;
    public Business(){}
    public Business(String companyName) {this.companyName = companyName; }
    // getters & setters
}

3. From AVSC file (json) via plugin Define schema in resources/avro and generate via avro-maven-plugin

Schema evolution

Type	Description
Backward	Old schema can be used to read New data
Forward	New schema can be used to read Old data
Full compatibility (Forward and Backward)	Both (Old & New) schemas can be used to read old & new data
Breaking	None of those
Target is type Full compatibility.

Important notes

1. Make your primary key required
2. Give default values to all the fields that could be removed in the future
3. Be very careful when using ENUM as the can not evolve over time
4. Do not rename fields. You can add aliases instead
5. When evolving schema, ALWAYS give default values
6. When evolving schema, NEVER remove, rename of the required field or change the type

Compatibility changes

Forward (common)

• Update producer to next version
• Takes time to update consumers

Backward

• Update all producers, but still able to read previous version producer data
• When all consumers update, update all producers

Refs & Sources:

• Confluent docs
• Stephane Maarek
• REST Proxy