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karapace. Your Kafka essentials in one tool.

An open-source implementation of Kafka REST and Schema Registry.

Tests Contributor Covenant


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 rest provides a RESTful interface to your Kafka cluster, allowing you to perform tasks such as producing and consuming messages and perform administrative cluster work, all the while using the language of the WEB.


  • Drop in replacement both on pre-existing Schema Registry / Kafka Rest Proxy client and server-sides
  • Moderate memory consumption
  • Asynchronous architecture based on aiohttp
  • Supports Avro and JSON Schema. Protobuf development is tracked with Issue 67.
  • Leader/Replica architecture for HA and load balancing.

Compatibility details

Karapace is compatible with Schema Registry 6.1.1 on API level. When a new version of SR is released, the goal is to support it in a reasonable time. Karapace supports all operations in the API. The goal is that even the error messages are the same as in Schema Registry, which cannot be always fully guaranteed.


Using Docker

To get you up and running with the latest release of Karapace, a docker setup is available:

docker-compose -f ./container/docker-compose.yml up -d

Then you should be able to reach two sets of endpoints:


Each configuration key can be overridden with an environment variable prefixed with KARAPACE_, exception being configuration keys that actually start with the karapace string. For example, to override the bootstrap_uri config value, one would use the environment variable KARAPACE_BOOTSTRAP_URI. Here you can find an example configuration file to give you an idea what you need to change.

Source install

Alternatively you can do a source install using:

python install


To register the first version of a schema under the subject "test" using Avro schema:

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

To register a version of a schema using JSON Schema, one needs to use schemaType property:

$ curl -X POST -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  --data '{"schemaType": "JSON", "schema": "{\"type\": \"object\",\"properties\":{\"age\":{\"type\": \"number\"}},\"additionalProperties\":true}"}' \

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

List topics:

$ curl "http://localhost:8081/topics"

Get info for one particular topic:

$ curl "http://localhost:8081/topics/my_topic"

Produce a message backed up by schema registry:

$ curl -H "Content-Type: application/vnd.kafka.avro.v2+json" -X POST -d \
  '{"value_schema": "{\"namespace\": \"example.avro\", \"type\": \"record\", \"name\": \"simple\", \"fields\": \
  [{\"name\": \"name\", \"type\": \"string\"}]}", "records": [{"value": {"name": "name0"}}]}' http://localhost:8081/topics/my_topic

Create a consumer:

$ curl -X POST -H "Content-Type: application/vnd.kafka.v2+json" -H "Accept: application/vnd.kafka.v2+json" \
  --data '{"name": "my_consumer", "format": "avro", "auto.offset.reset": "earliest"}' \

Subscribe to the topic we previously published to:

$ curl -X POST -H "Content-Type: application/vnd.kafka.v2+json" --data '{"topics":["my_topic"]}' \

Consume previously published message:

$ curl -X GET -H "Accept: application/vnd.kafka.avro.v2+json" \

Commit offsets for a particular topic partition:

$ curl -X POST -H "Content-Type: application/vnd.kafka.v2+json" --data '{}' \

Delete consumer:

$ curl -X DELETE -H "Accept: application/vnd.kafka.v2+json" \

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.

Karapace includes a tool to backing up and restoring data. To back up, run:

karapace_schema_backup get --config karapace.config.json --location schemas.log

You can also back up the data by using 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

Your backup can be restored with Karapace by running:

karapace_schema_backup restore --config karapace.config.json --location schemas.log

Or Kafka's Java console producer can 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

Performance comparison to Confluent stack


  • 50 concurrent connections, 50.000 requests
Format Karapace Confluent
Avro 80.95 7.22
Binary 66.32 46.99
Json 60.36 53.7
  • 15 concurrent connections, 50.000 requests
Format Karapace Confluent
Avro 25.05 18.14
Binary 21.35 15.85
Json 21.38 14.83
  • 4 concurrent connections, 50.000 requests
Format Karapace Confluent
Avro 6.54 5.67
Binary 6.51 4.56
Json 6.86 5.32

Also, it appears there is quite a bit of variation on subsequent runs, especially for the lower numbers, so once more exact measurements are required, it's advised we increase the total req count to something like 500K

We'll focus on avro serialization only after this round, as it's the more expensive one, plus it tests the entire stack

Consuming RAM

A basic push pull test , with 12 connections on the publisher process and 3 connections on the subscriber process, with a 10 minute duration. The publisher has the 100 ms timeout and 100 max_bytes parameters set on each request so both processes have work to do Heap size limit is set to 256M on Rest proxy

Ram consumption, different consumer count, over 300s

Consumers Karapace combined Confluent rest
1 47 200
10 55 400
20 83 530


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

Keys to take special care are the ones needed to configure Kafka and advertised_hostname.

Parameter Default Value Description
advertised_hostname 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 localhost:9092 The URI to the Kafka service where to store the schemas and to run coordination among the Karapace instances.
client_id 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.
consumer_enable_autocommit True Enable auto commit on rest proxy consumers
consumer_request_timeout_ms 11000 Rest proxy consumers timeout for reads that do not limit the max bytes or provide their own timeout
consumer_request_max_bytes 67108864 Rest proxy consumers maximum bytes to be fetched per request
fetch_min_bytes -1 Rest proxy consumers minimum bytes to be fetched per request. -1 means no limit
group_id 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.
producer_compression_type None Type of compression to be used by rest proxy producers
producer_acks 1 Level of consistency desired by each producer message sent on the rest proxy. More on Kafka Producer
producer_linger_ms 0 Time to wait for grouping together requests. More on Kafka Producer
security_protocol PLAINTEXT Default Kafka security protocol needed to communicate with the Kafka cluster. Other options is to use SSL for SSL client certificate authentication.
sentry None Used to configure parameters for sentry integration (dsn, tags, ...). Setting the environment variable SENTRY_DSN will also enable sentry integration.
ssl_cafile /path/to/cafile Used when security_protocol is set to SSL, the path to the SSL CA certificate.
ssl_certfile /path/to/certfile Used when security_protocol is set to SSL, the path to the SSL certfile.
ssl_keyfile /path/to/keyfile Used when security_protocol is set to SSL, the path to the SSL keyfile.
topic_name _schemas The name of the Kafka topic where to store the schemas.
replication_factor 1 The replication factor to be used with the schema topic.
host Address to bind the Karapace HTTP server to. Set to an empty string to listen to all available addresses.
registry_host Kafka Registry host, used by Kafka Rest for avro related requests. If running both in the same process, it should be left to its default value
port 8081 HTTP webserver port to bind the Karapace to.
registry_port 8081 Kafka Registry port, used by Kafka Rest for avro related requests. If running both in the same process, it should be left to its default value
metadata_max_age_ms 60000 Period of time in milliseconds after Kafka metadata is force refreshed.
karapace_rest true If the rest part of the app should be included in the starting process At least one of this and karapace_registry options need to be enabled in order for the service to start
karapace_registry true If the registry part of the app should be included in the starting process At least one of this and karapace_rest options need to be enabled in order for the service to start
name_strategy subject_name Name strategy to use when storing schemas from the kafka rest proxy service
master_election_strategy lowest Decides on what basis the Karapace cluster master is chosen (only relevant in a multi node setup)


To unistall Karapace from the system you can follow the instructions described below. We would love to hear your reasons for uninstalling though. Please file an issue if you experience any problems or email us with feedback

Installed via Docker

If you installed Karapace via Docker, you would need to first stop and remove the images like described:

First obtain the container IDs related to Karapace, you should have one for the registry itself and another one for the rest interface:

docker ps | grep karapace

After this, you can stop each of the containers with:

docker stop <CONTAINER_ID>

If you don't need or want to have the Karapace images around you can now proceed to delete them using:

docker rm <CONTAINER_ID>

Installed from Sources

If you installed Karapace from the sources via python install, it can be uninstalled with the following pip command:

pip uninstall karapace


Karapace is licensed under the Apache license, version 2.0. 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 ⓒ 2021 Aiven Ltd.