Utility for your CI/CD process to validate, register or delete Kafka protobuf schemes in the registry.

Schema registry mainly operates with the “subject” concept related to a topic. Therefore, key and value schemes are related to the subject. This utility uses TopicRecordNameStrategy, which means that the subject for the value is defined as <topic name>-<fully-qualified record name>-value. This utility operates only with topic and record values and hides subject name generation. Also, the ability to create schemes for the topic keys is not realized for now.


  • validate – Validates the topic to exist and the schema changes compatibility with existing version.
  • register – Creates a subject, if one does not exist, sets a scheme for a subject or updates it.
  • subjects – Lists available subjects for the topic.
  • versions – Lists available versions for the subject.
  • inspect – Outputs all information about the subject.
  • export – Exports the schema value to the local file.

The application is being configured via CLI flags, environment variables or dotenv file.


  1. Loads protobuf file (--proto).
  2. Validates for the topic existence. The schema is considered to be valid, if the topic does not exist.
  3. Validates for the subject existence. The schema is considered to be valid, if the subject does not exist in Schema Registry.
  4. Calls Schema Registry to verify the compatibility of the new version of the schema.

Example schema validate --proto message.proto --topic current_weather --cluster localhost:9092 --sr http://localhost:8081.

Try to check Compatibility level and fix it if updated schema is not compatible with the previous one despite of mistakes absence:

curl -X PUT -H "Content-Type: application/vnd.schemaregistry.v1+json" --data '{"compatibility": "FORWARD"}' http://localhost:8081/config


Performs the same steps as “validate” command and registers the scheme or new version in the end.

Example schema register --proto schema.proto --topic current_weather --cluster localhost:9092 --sr http://localhost:8081.


Lists available subjects for the topic.

Example schema subjects --topic current_weather --sr http://localhost:8081.


Lists available versions for the subject.

Example schema versions --topic current_weather --sr http://localhost:8081.


Outputs all information about the subject: versions list, id and the scheme value. The version by default is latest.

Example schema inspect --topic current_weather --sr http://localhost:8081 --version=1.


Exports the schema value to the local file. Schema version is to be set with --version flag orlatest by default. The command can be used for the automation of code generation on combination with protoc utility.

Example schema export --topic current_weather --sr http://localhost:8081 --version=1 --output message.proto.

How to set topic and record

Topic&record can be set with CLI flags, environmental variables or with proto file.

The common flags:

  • Topic: flag --topic or variable TOPIC.
  • Record: flag--record or variable RECORD.

Topic&record definition with proto file

For CI/CD automation you can set the separate topic&record values for the each schema with option field in the proto file. More information about Protobuf options can be found in the Protocol Buffers documentation.


syntax = "proto3";

import "google/protobuf/descriptor.proto";

extend google.protobuf.MessageOptions {
  string topic = 50001;
  string record = 50002;

message Currency {
  option (topic) = "weather";
  option (record) = "currency";

  string value = 1;

The utility would use Protobuf options if the flags --topic and --recourd are not present.

If your service uses several schemes for the one topic you need to place the to the separate proto files. The options must be defined single time as in the following example.

syntax = "proto3";

package producer1;

option go_package = "main";

import "google/protobuf/descriptor.proto";

extend google.protobuf.MessageOptions {
  string topic = 50001;
  string record = 50002;

The options signatures would be loaded withimport "topic_option.proto"; in every message definition file.

How to get options values in the code

  1. Message code must be generated with the standard protoc utility.
  2. The topic&record option values can be accessed with the following code.

package main

import (

func main() {

func getTopicRecord(m interface{}) (string, string) {
	_, md := descriptor.MessageDescriptorProto(m)
	record := proto.GetExtension(md.GetOptions(), E_Record)
	topic := proto.GetExtension(md.GetOptions(), E_Topic)
	return topic.(string), record.(string)

HereCurrency is the model generated within the previous section.

Another way to get values is to use lib/protoschema.ExtractTopicRecord function.



Utility gets configuration values with CLI flags (e.g. --sr http://localhost:8081) or with environmental variables (e.g. SCHEMA_REGISTRY=http://localhost:8081).

The common environmental variables SCHEMA_REGISTRY and CLUSTER can be placed to the dotenv file located with SCHEMA_CONFIG=/home/user/.schema_config env variable.


Run with docker:

docker run youlatech/schema:latest schema

Local build

go build -ldflags="-X 'main.Version=0.5'" -o schema ./cmd/schema/*.go

The last binary can also be downloaded from the releases page.


Example for the GitLab CI:

  image: youlatech/schema:latest
    - schema validate --proto services/$PROTO --cluster ${KAFKA_CLUSTER} --sr ${SR}
    PROTO: producer1/cmd/producer1/weather_message.proto

How to run Confluent Schema Registry.

You can try to set up local Confluent Schema registry environment with the Confluent docker-compose example.


View Github