Apache Kafka

Detailed documentation on the Apache Kafka pubsub component

Component format

To set up Apache Kafka pub/sub, create a component of type pubsub.kafka. See the pub/sub broker component file to learn how ConsumerID is automatically generated. Read the How-to: Publish and Subscribe guide on how to create and apply a pub/sub configuration.

All component metadata field values can carry templated metadata values, which are resolved on Dapr sidecar startup. For example, you can choose to use {namespace} as the consumerGroup to enable using the same appId in different namespaces using the same topics as described in this article.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "{namespace}"
  - name: consumerID # Optional. If not supplied, runtime will create one.
    value: "channel1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "password"
  - name: saslUsername # Required if authType is `password`.
    value: "adminuser"
  - name: saslPassword # Required if authType is `password`.
    secretKeyRef:
      name: kafka-secrets
      key: saslPasswordSecret
  - name: saslMechanism
    value: "SHA-512"
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 2.0.0
  - name: disableTls # Optional. Disable TLS. This is not safe for production!! You should read the `Mutual TLS` section for how to use TLS.
    value: "true"
  - name: schemaRegistryURL # Optional. When using Schema Registry Avro serialization/deserialization. The Schema Registry URL.
    value: http://localhost:8081
  - name: schemaRegistryAPIKey # Optional. When using Schema Registry Avro serialization/deserialization. The Schema Registry API Key.
    value: XYAXXAZ
  - name: schemaRegistryAPISecret # Optional. When using Schema Registry Avro serialization/deserialization. The Schema Registry credentials API Secret.
    value: "ABCDEFGMEADFF"
  - name: schemaCachingEnabled # Optional. When using Schema Registry Avro serialization/deserialization. Enables caching for schemas.
    value: true
  - name: schemaLatestVersionCacheTTL # Optional. When using Schema Registry Avro serialization/deserialization. The TTL for schema caching when publishing a message with latest schema available.
    value: 5m
  

For details on using secretKeyRef, see the guide on how to reference secrets in components.

Spec metadata fields

Field Required Details Example
brokers Y A comma-separated list of Kafka brokers. "localhost:9092,dapr-kafka.myapp.svc.cluster.local:9093"
consumerGroup N A kafka consumer group to listen on. Each record published to a topic is delivered to one consumer within each consumer group subscribed to the topic. If a value for consumerGroup is provided, any value for consumerID is ignored - a combination of the consumer group and a random unique identifier will be set for the consumerID instead. "group1"
consumerID N Consumer ID (consumer tag) organizes one or more consumers into a group. Consumers with the same consumer ID work as one virtual consumer; for example, a message is processed only once by one of the consumers in the group. If the consumerID is not provided, the Dapr runtime set it to the Dapr application ID (appID) value. If a value for consumerGroup is provided, any value for consumerID is ignored - a combination of the consumer group and a random unique identifier will be set for the consumerID instead. "channel1"
clientID N A user-provided string sent with every request to the Kafka brokers for logging, debugging, and auditing purposes. Defaults to "namespace.appID" for Kubernetes mode or "appID" for Self-Hosted mode. "my-namespace.my-dapr-app", "my-dapr-app"
authRequired N Deprecated Enable SASL authentication with the Kafka brokers. "true", "false"
authType Y Configure or disable authentication. Supported values: none, password, mtls, oidc or awsiam "password", "none"
saslUsername N The SASL username used for authentication. Only required if authType is set to "password". "adminuser"
saslPassword N The SASL password used for authentication. Can be secretKeyRef to use a secret reference. Only required if authType is set to “password”`. "", "KeFg23!"
saslMechanism N The SASL Authentication Mechanism you wish to use. Only required if authType is set to "password". Defaults to PLAINTEXT "SHA-512", "SHA-256", "PLAINTEXT"
initialOffset N The initial offset to use if no offset was previously committed. Should be “newest” or “oldest”. Defaults to “newest”. "oldest"
maxMessageBytes N The maximum size in bytes allowed for a single Kafka message. Defaults to 1024. 2048
consumeRetryInterval N The interval between retries when attempting to consume topics. Treats numbers without suffix as milliseconds. Defaults to 100ms. 200ms
consumeRetryEnabled N Disable consume retry by setting "false" "true", "false"
version N Kafka cluster version. Defaults to 2.0.0. Note that this must be set to 1.0.0 if you are using Azure EventHubs with Kafka. 0.10.2.0
caCert N Certificate authority certificate, required for using TLS. Can be secretKeyRef to use a secret reference "-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"
clientCert N Client certificate, required for authType mtls. Can be secretKeyRef to use a secret reference "-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"
clientKey N Client key, required for authType mtls Can be secretKeyRef to use a secret reference "-----BEGIN RSA PRIVATE KEY-----\n<base64-encoded PKCS8>\n-----END RSA PRIVATE KEY-----"
skipVerify N Skip TLS verification, this is not recommended for use in production. Defaults to "false" "true", "false"
disableTls N Disable TLS for transport security. To disable, you’re not required to set value to "true". This is not recommended for use in production. Defaults to "false". "true", "false"
oidcTokenEndpoint N Full URL to an OAuth2 identity provider access token endpoint. Required when authType is set to oidc https://identity.example.com/v1/token"
oidcClientID N The OAuth2 client ID that has been provisioned in the identity provider. Required when authType is set to oidc dapr-kafka
oidcClientSecret N The OAuth2 client secret that has been provisioned in the identity provider: Required when authType is set to oidc "KeFg23!"
oidcScopes N Comma-delimited list of OAuth2/OIDC scopes to request with the access token. Recommended when authType is set to oidc. Defaults to "openid" "openid,kafka-prod"
oidcExtensions N Input/Output String containing a JSON-encoded dictionary of OAuth2/OIDC extensions to request with the access token
awsRegion N The AWS region where the Kafka cluster is deployed to. Required when authType is set to awsiam us-west-1
awsAccessKey N AWS access key associated with an IAM account. "accessKey"
awsSecretKey N The secret key associated with the access key. "secretKey"
awsSessionToken N AWS session token to use. A session token is only required if you are using temporary security credentials. "sessionToken"
awsIamRoleArn N IAM role that has access to AWS Managed Streaming for Apache Kafka (MSK). This is another option to authenticate with MSK aside from the AWS Credentials. "arn:aws:iam::123456789:role/mskRole"
awsStsSessionName N Represents the session name for assuming a role. "MSKSASLDefaultSession"
schemaRegistryURL N Required when using Schema Registry Avro serialization/deserialization. The Schema Registry URL. http://localhost:8081
schemaRegistryAPIKey N When using Schema Registry Avro serialization/deserialization. The Schema Registry credentials API Key. XYAXXAZ
schemaRegistryAPISecret N When using Schema Registry Avro serialization/deserialization. The Schema Registry credentials API Secret. ABCDEFGMEADFF
schemaCachingEnabled N When using Schema Registry Avro serialization/deserialization. Enables caching for schemas. Default is true true
schemaLatestVersionCacheTTL N When using Schema Registry Avro serialization/deserialization. The TTL for schema caching when publishing a message with latest schema available. Default is 5 min 5m

The secretKeyRef above is referencing a kubernetes secrets store to access the tls information. Visit here to learn more about how to configure a secret store component.

Note

The metadata version must be set to 1.0.0 when using Azure EventHubs with Kafka.

Authentication

Kafka supports a variety of authentication schemes and Dapr supports several: SASL password, mTLS, OIDC/OAuth2. With the added authentication methods, the authRequired field has been deprecated from the v1.6 release and instead the authType field should be used. If authRequired is set to true, Dapr will attempt to configure authType correctly based on the value of saslPassword. The valid values for authType are:

  • none
  • password
  • certificate
  • mtls
  • oidc
  • awsiam

None

Setting authType to none will disable any authentication. This is NOT recommended in production.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-noauth
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "none"
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 0.10.2.0
  - name: disableTls
    value: "true"

SASL Password

Setting authType to password enables SASL authentication. This requires setting the saslUsername and saslPassword fields.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-sasl
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "password"
  - name: saslUsername # Required if authType is `password`.
    value: "adminuser"
  - name: saslPassword # Required if authType is `password`.
    secretKeyRef:
      name: kafka-secrets
      key: saslPasswordSecret
  - name: saslMechanism
    value: "SHA-512"
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 0.10.2.0
  - name: caCert
    secretKeyRef:
      name: kafka-tls
      key: caCert

Mutual TLS

Setting authType to mtls uses a x509 client certificate (the clientCert field) and key (the clientKey field) to authenticate. Note that mTLS as an authentication mechanism is distinct from using TLS to secure the transport layer via encryption. mTLS requires TLS transport (meaning disableTls must be false), but securing the transport layer does not require using mTLS. See Communication using TLS for configuring underlying TLS transport.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-mtls
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "mtls"
  - name: caCert
    secretKeyRef:
      name: kafka-tls
      key: caCert
  - name: clientCert
    secretKeyRef:
      name: kafka-tls
      key: clientCert
  - name: clientKey
    secretKeyRef:
      name: kafka-tls
      key: clientKey
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 0.10.2.0

OAuth2 or OpenID Connect

Setting authType to oidc enables SASL authentication via the OAUTHBEARER mechanism. This supports specifying a bearer token from an external OAuth2 or OIDC identity provider. Currently, only the client_credentials grant is supported.

Configure oidcTokenEndpoint to the full URL for the identity provider access token endpoint.

Set oidcClientID and oidcClientSecret to the client credentials provisioned in the identity provider.

If caCert is specified in the component configuration, the certificate is appended to the system CA trust for verifying the identity provider certificate. Similarly, if skipVerify is specified in the component configuration, verification will also be skipped when accessing the identity provider.

By default, the only scope requested for the token is openid; it is highly recommended that additional scopes be specified via oidcScopes in a comma-separated list and validated by the Kafka broker. If additional scopes are not used to narrow the validity of the access token, a compromised Kafka broker could replay the token to access other services as the Dapr clientID.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "oidc"
  - name: oidcTokenEndpoint # Required if authType is `oidc`.
    value: "https://identity.example.com/v1/token"
  - name: oidcClientID      # Required if authType is `oidc`.
    value: "dapr-myapp"
  - name: oidcClientSecret  # Required if authType is `oidc`.
    secretKeyRef:
      name: kafka-secrets
      key: oidcClientSecret
  - name: oidcScopes        # Recommended if authType is `oidc`.
    value: "openid,kafka-dev"
  - name: caCert            # Also applied to verifying OIDC provider certificate
    secretKeyRef:
      name: kafka-tls
      key: caCert
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 0.10.2.0

AWS IAM

Authenticating with AWS IAM is supported with MSK. Setting authType to awsiam uses AWS SDK to generate auth tokens to authenticate.

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-awsiam
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "awsiam"
  - name: awsRegion # Required.
    value: "us-west-1"
  - name: awsAccessKey # Optional.
    value: <AWS_ACCESS_KEY>
  - name: awsSecretKey # Optional.
    value: <AWS_SECRET_KEY>
  - name: awsSessionToken # Optional.
    value: <AWS_SESSION_KEY>
  - name: awsIamRoleArn # Optional.
    value: "arn:aws:iam::123456789:role/mskRole"
  - name: awsStsSessionName # Optional.
    value: "MSKSASLDefaultSession"

Communication using TLS

By default TLS is enabled to secure the transport layer to Kafka. To disable TLS, set disableTls to true. When TLS is enabled, you can control server certificate verification using skipVerify to disable verification (NOT recommended in production environments) and caCert to specify a trusted TLS certificate authority (CA). If no caCert is specified, the system CA trust will be used. To also configure mTLS authentication, see the section under Authentication. Below is an example of a Kafka pubsub component configured to use transport layer TLS:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: brokers # Required. Kafka broker connection setting
    value: "dapr-kafka.myapp.svc.cluster.local:9092"
  - name: consumerGroup # Optional. Used for input bindings.
    value: "group1"
  - name: clientID # Optional. Used as client tracing ID by Kafka brokers.
    value: "my-dapr-app-id"
  - name: authType # Required.
    value: "certificate"
  - name: consumeRetryInterval # Optional.
    value: 200ms
  - name: version # Optional.
    value: 0.10.2.0
  - name: maxMessageBytes # Optional.
    value: 1024
  - name: caCert # Certificate authority certificate.
    secretKeyRef:
      name: kafka-tls
      key: caCert
auth:
  secretStore: <SECRET_STORE_NAME>

Consuming from multiple topics

When consuming from multiple topics using a single pub/sub component, there is no guarantee about how the consumers in your consumer group are balanced across the topic partitions.

For instance, let’s say you are subscribing to two topics with 10 partitions per topic and you have 20 replicas of your service consuming from the two topics. There is no guarantee that 10 will be assigned to the first topic and 10 to the second topic. Instead, the partitions could be divided unequally, with more than 10 assigned to the first topic and the rest assigned to the second topic.

This can result in idle consumers listening to the first topic and over-extended consumers on the second topic, or vice versa. This same behavior can be observed when using auto-scalers such as HPA or KEDA.

If you run into this particular issue, it is recommended that you configure a single pub/sub component per topic with uniquely defined consumer groups per component. This guarantees that all replicas of your service are fully allocated to the unique consumer group, where each consumer group targets one specific topic.

For example, you may define two Dapr components with the following configuration:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-topic-one
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: consumerGroup
    value: "{appID}-topic-one"
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: kafka-pubsub-topic-two
spec:
  type: pubsub.kafka
  version: v1
  metadata:
  - name: consumerGroup
    value: "{appID}-topic-two"

Sending and receiving multiple messages

Apache Kafka component supports sending and receiving multiple messages in a single operation using the bulk Pub/sub API.

Configuring bulk subscribe

When subscribing to a topic, you can configure bulkSubscribe options. Refer to Subscribing messages in bulk for more details. Learn more about the bulk subscribe API.

Apache Kafka supports the following bulk metadata options:

Configuration Default
maxBulkAwaitDurationMs 10000 (10s)
maxBulkSubCount 80

Per-call metadata fields

Partition Key

When invoking the Kafka pub/sub, its possible to provide an optional partition key by using the metadata query param in the request url.

The param name is partitionKey.

Example:

curl -X POST http://localhost:3500/v1.0/publish/myKafka/myTopic?metadata.partitionKey=key1 \
  -H "Content-Type: application/json" \
  -d '{
        "data": {
          "message": "Hi"
        }
      }'

Message headers

All other metadata key/value pairs (that are not partitionKey) are set as headers in the Kafka message. Here is an example setting a correlationId for the message.

curl -X POST http://localhost:3500/v1.0/publish/myKafka/myTopic?metadata.correlationId=myCorrelationID&metadata.partitionKey=key1 \
  -H "Content-Type: application/json" \
  -d '{
        "data": {
          "message": "Hi"
        }
      }'

Avro Schema Registry serialization/deserialization

You can configure pub/sub to publish or consume data encoded using Avro binary serialization, leveraging an Apache Schema Registry (for example, Confluent Schema Registry, Apicurio).

Configuration

When configuring the Kafka pub/sub component metadata, you must define:

  • The schema registry URL
  • The API key/secret, if applicable

Schema subjects are automatically derived from topic names, using the standard naming convention. For example, for a topic named my-topic, the schema subject will be my-topic-value. When interacting with the message payload within the service, it is in JSON format. The payload is transparently serialized/deserialized within the Dapr component. Date/Datetime fields must be passed as their Epoch Unix timestamp equivalent (rather than typical Iso8601). For example:

  • 2024-01-10T04:36:05.986Z should be passed as 1704861365986 (the number of milliseconds since Jan 1st, 1970)
  • 2024-01-10 should be passed as 19732 (the number of days since Jan 1st, 1970)

Publishing Avro messages

In order to indicate to the Kafka pub/sub component that the message should be using Avro serialization, the valueSchemaType metadata must be set to Avro.


curl -X "POST" http://localhost:3500/v1.0/publish/pubsub/my-topic?metadata.rawPayload=true&metadata.valueSchemaType=Avro -H "Content-Type: application/json" -d '{"order_number": "345", "created_date": 1704861365986}'

from dapr.clients import DaprClient

with DaprClient() as d:
    req_data = {
        'order_number': '345',
        'created_date': 1704861365986
    }
    # Create a typed message with content type and body
    resp = d.publish_event(
        pubsub_name='pubsub',
        topic_name='my-topic',
        data=json.dumps(req_data),
        publish_metadata={'rawPayload': 'true', 'valueSchemaType': 'Avro'}
    )
    # Print the request
    print(req_data, flush=True)

Subscribing to Avro topics

In order to indicate to the Kafka pub/sub component that the message should be deserialized using Avro, the valueSchemaType metadata must be set to Avro in the subscription metadata.


from fastapi import APIRouter, Body, Response, status
import json
import sys

app = FastAPI()

router = APIRouter()


@router.get('/dapr/subscribe')
def subscribe():
    subscriptions = [{'pubsubname': 'pubsub',
                      'topic': 'my-topic',
                      'route': 'my_topic_subscriber',
                      'metadata': {
                          'rawPayload': 'true',
                          'valueSchemaType': 'Avro',
                      } }]
    return subscriptions

@router.post('/my_topic_subscriber')
def my_topic_subscriber(event_data=Body()):
    print(event_data, flush=True)
      return Response(status_code=status.HTTP_200_OK)

app.include_router(router)

Create a Kafka instance


You can run Kafka locally using this Docker image. To run without Docker, see the getting started guide here.


To run Kafka on Kubernetes, you can use any Kafka operator, such as Strimzi.