# Avro and schema

This guide will show you how to do various schema operations on your Kafka topics.

> **Note**
> The easiest way to communicate with the API is to use `curl` from one of your Kafka-pods, so that you have easy access to both the schema registry URL and the username/password.

## Register schema

To register the first version of a schema under the subject "team.test-key" using **Avro schema**:

```
$ curl -X POST -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  --data '{"schema": "{\"type\": \"record\", \"name\": \"Obj\", \"fields\":[{\"name\": \"age\", \"type\": \"int\"}]}"}' \
  $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key/versions
```

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

```
$ curl -X POST -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  --data '{"schemaType": "JSON", "schema": "{\"type\": \"object\",\"properties\":{\"age\":{\"type\": \"number\"}},\"additionalProperties\":true}"}' \
  $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key/versions
```

## List versions of a schema

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

```
$ curl -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key/versions
```

## Fetch specific version of a schema

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

```
$ curl -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key/versions/1
```

## Delete schema

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

```
$ curl -X DELETE -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key/versions/10
  10
```

To delete all versions of the schema registered under subject "team.test-key":

```
$ curl -X DELETE -u $KAFKA_SCHEMA_REGISTRY_USER:$KAFKA_SCHEMA_REGISTRY_PASSWORD $KAFKA_SCHEMA_REGISTRY/subjects/team.test-key
  [1]
```

## REST API

For applications that can't use Kafka directly, a REST API is possible.
Because of security implications, we have not enabled the REST API on the cluster, but interested parties may run their own instance.

We have packaged [Aivens Karapace](https://github.com/aiven/karapace) project in a Nais-friendly package.
Teams can install [Karapace](https://github.com/nais/karapace) in their own namespace with relevant access to provide a REST API for Kafka topics.
Check the Karapace Readme for details.