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Karapace BuildStatus

karapace Your Kafka essentials in one tool


  • Schema Registry that is 1:1 Compatible with the pre-existing proprietary Confluent Schema Registry
  • Drop in replacement both on pre-existing Schema Registry client and server-sides
  • Moderate memory consumption
  • Asynchronous architecture based on aiohttp


Karapace supports the storing of schemas in a central repository, which clients can access to serialize and deserialize messages. The schemas also maintain their own version histories and can be checked for compatibility between their different respective versions.


Karapace requires Python 3.6 or later and some additional components in order to operate:

  • aiohttp for serving schemas over HTTP in an asynchronous fashion
  • avro-python3 for Avro serialization
  • kafka-python to read, write and coordinate Karapace's persistence in Kafka

Developing and testing Karapace also requires the following utilities: requests, flake8, pylint and pytest.

Karapace has been developed and tested on modern Linux x86-64 systems, but should work on other platforms that provide the required modules.


To build an installation package for your distribution, go to the root directory of a Karapace Git checkout and run:


make rpm

This will produce a .rpm package usually into rpm/RPMS/noarch/.


python3 bdist_egg

This will produce an egg file into a dist directory within the same folder.


To install it run as root:


dnf install rpm/RPMS/noarch/*

On Linux systems it is recommended to simply run karapace under systemd:

systemctl enable karapace.service

and eventually after the setup section, you can just run:

systemctl start karapace.service


easy_install dist/karapace-0.1.0-py3.6.egg


After this you need to create a suitable JSON configuration file for your installation. Keys to take special care are the ones needed to configure Kafka and advertised_hostname.

To see descriptions of configuration keys see section config. Here's an example configuration file to give you an idea what you need to change:

    "advertised_hostname": "localhost",
    "bootstrap_uri": "",
    "client_id": "sr-1",
    "compatibility": "FULL",
    "group_id": "schema-registry",
    "host": "",
    "log_level": "DEBUG",
    "port": 8081,
    "master_eligibility": true,
    "replication_factor": 1,
    "security_protocol": "PLAINTEXT",
    "ssl_cafile": null,
    "ssl_certfile": null,
    "ssl_keyfile": null,
    "topic_name": "_schemas"


To Register the first version of a schema under the subject "test":

$ curl -X POST -H "Content-Type: application/vnd.schemaregistry.v1+json" \
--data '{"schema": "{\"type\": \"record\", \"name\": \"Obj\", \"fields\":[{\"name\": \"age\", \"type\": \"int\"}]}"}' \

To list all subjects (including the one created just above):

$ curl -X GET http://localhost:8081/subjects

To list all the versions of a given schema (including the one just created above):

$ curl -X GET http://localhost:8081/subjects/test-key/versions

To fetch back the schema whose global id is 1 (i.e. the one registered above):

$ curl -X GET http://localhost:8081/schemas/ids/1

To get the specific version 1 of the schema just registered run:

$ curl -X GET http://localhost:8081/subjects/test-key/versions/1

To get the latest version of the schema under subject test-key run:

$ curl -X GET http://localhost:8081/subjects/Kafka-value/versions/latest

In order to delete version 10 of the schema registered under subject "test-key" (if it exists):

$ curl -X DELETE http://localhost:8081/subjects/test-key/versions/10

To Delete all versions of the schema registered under subject "test-key":

$ curl -X DELETE http://localhost:8081/subjects/test-key

Test the compatibility of a schema with the latest schema under subject "test-key":

$ curl -X POST -H "Content-Type: application/vnd.schemaregistry.v1+json" \
    --data '{"schema": "{\"type\": \"int\"}"}' \

Get current global backwards compatibility setting value:

$ curl -X GET http://localhost:8081/config

Change compatibility requirements for all subjects where it's not specifically defined otherwise:

$ curl -X PUT -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  --data '{"compatibility": "NONE"}' http://localhost:8081/config

Change compatibility requirement to FULL for the test-key subject:

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

Backing up your Karapace

Karapace natively stores its data in a Kafka topic the name of which you can configure freely but which by default is called _schemas.

To easily back up the data in the topic you can run Kafka's Java console consumer:

./ --bootstrap-server brokerhostname:9092 --topic _schemas --from-beginning --property print.key=true --timeout-ms 1000 1> schemas.log

Restoring Karapace from backup

Kafka's Java console producer can then in turn be used to restore the data to a new Kafka cluster.

You can restore the data from the previous step by running:

./ --broker-list brokerhostname:9092 --topic _schemas --property parse.key=true < schemas.log


Once installed, the karapace program should be in your path. It is the main daemon process that should be run under a service manager such as systemd to serve clients.

Configuration keys

advertised_hostname (default socket.gethostname())

The hostname being advertised to other instances of Karapace that are attached to the same Kafka group. All nodes within the cluster need to have their advertised_hostname's set so that they can all reach each other.

bootstrap_uri (default localhost:9092)

The URI to the Kafka service where to store the schemas and to run coordination among the Karapace instances.

client_id (default sr-1)

The client_id name by which the Karapace will use when coordinating with other Karapaces who is master. The one with the name that sorts as the first alphabetically is chosen as master from among the services with master_eligibility set to true.

group_id (default schema-registry)

The Kafka group name used for selecting a master service to coordinate the storing of Schemas.

master_eligibility (true)

Should the service instance be considered for promotion to be the master service. Reason to turn this off would be to have an instances of Karapace running somewhere else for HA purposes but which you wouldn't want to automatically promote to master if the primary instances were to become unavailable.

security_protocol (default PLAINTEXT)

Default Kafka security protocol needed to communicate with the Kafka cluster. Other options is to use SSL for SSL client certificate authentication.

ssl_cafile (default Path to CA certificate)

Used when security_protocol is set to SSL, the path to the SSL CA certificate.

ssl_certfile (default /path/to/certfile)

Used when security_protocol is set to SSL, the path to the SSL certfile.

ssl_keyfile (default /path/to/keyfile)

Used when security_protocol is set to SSL, the path to the SSL keyfile.

topic_name (default _schemas)

The name of the Kafka topic where to store the schemas.

replication_factor (default 1)

The replication factor to be used with the schema topic.

host (default "")

Address to bind the Karapace HTTP server to. Set to an empty string to listen to all available addresses.

port (default 8081)

HTTP webserver port to bind the Karapace to.


Karapace is licensed under the AGPL, version 3. Full license text is available in the LICENSE file.

Please note that the project explicitly does not require a CLA (Contributor License Agreement) from its contributors.


Bug reports and patches are very welcome, please post them as GitHub issues and pull requests at . Any possible vulnerabilities or other serious issues should be reported directly to the maintainers <>.


Karapace was created by, and is maintained by, Aiven cloud data hub developers.

The schema storing part of Karapace loans heavily from the ideas of the earlier Schema Registry implementation by Confluent and thanks are in order to them for pioneering the concept.

Recent contributors are listed on the GitHub project page,

Copyright ⓒ 2019 Aiven Ltd.

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