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Kafka Connections

This README describes the implementation of this common/kafka package. Primarily the implementation is focused on providing utilities for creating the basic connections (i.e. AdminClient, Producer, Consumer) used in a Kafka based solution. The solution provides support for various Kafka implementations / deployments both with and without authentication. Further, the implementation provides support for administering Azure EventHubs (Topics) via the standard Sarama ClusterAdmin interface so that the users of this logic do not have to concern themselves with the underlying implementation. Finally, support is provided for users to implement their own "custom" AdminClient functionality via a simple sidecar Container.

AdminClient & K8S Secrets

The AdminClient expects there to be a single K8S Secret which by default is named kafka-cluster and exists in the knative-eventing namespace (this may be changed by altering the kafka.authSecretName and/or the kafka.authSecretNamespace in the ConfigMap) , containing the following fields...

data:
    password:  SASL Password or Azure Connection String of Azure Namespace
    username:  SASL Username or '$ConnectionString' for Azure Namespace
    namespace: Only required for Azure AdminClient usage - specifies the Azure EventHub Namespace

Note - The username and password fields from the Kubernetes Secret will override any similar values provided in the sarama section of the ConfigMap.

Producer / Consumer

The Kafka Producer and Consumer are simpler and expect to be provided the specific Broker string and SASL Username and Password (if used). It is expected that the utilities exposed by the custom AdminClient in this implementation can be used to get the name of the Kafka Secret for a specific Topic / EventHub which can then be used to acquire the needed information.

EventHubs (Azure)

While Azure EventHubs support the standard Kafka interfaces for Producer / Consumer based event transmission, it does not yet provide a similar management layer. Instead, users are required to either use their REST API or the go-client. The go-client is easier to use but only provides limited EventHub related functionality (e.g. - No "namespace" management, etc...) This implementation is currently based on the go-client and expects Azure Namespaces to be manually allocated and pre-existing. Since Azure requires unique authentication for each EventHub Namespace, we are currently limited to supporting a single instance with its inherent limitations as to the number of Topics that can be created.

Custom (REST Sidecar)

If the standard Kafka administration of Topics via the Sarama ClusterAdmin is not sufficient, it is possible for a user to provide their own custom implementation via a Kubernetes "sidecar" Container. The eventing-kafka implementation will then proxy all Topic Create/Delete requests to the sidecar and convert responses for normal processing. The implementation of this sidecar is expected to explicitly adhere to the following design and implementation requirements in order for this proxying of requests to work successfully.

  1. Eventing-Kafka Configuration

    The following changes to the default config YAML will be required in order to deploy a custom sidecar as part of the eventing-kafka Controller Deployment...

    • ConfigMap: The data.eventing-kafka.kafka.adminType field in the ConfigMap must be set to custom. This tells eventing-kafka that it should proxy Topic creation and deletion requests to the expected sidecar endpoints as defined below.

    • Deployment: The sidecar Container will need to be added to the Controller Deployment along with any other supporting infrastructure (VolumeMounts, etc.).

    • Service Account: The default ServiceAccount is used by the Controller Deployment to pull images. This ServiceAccount will need to be updated to include any imagePullSecrets required to pull the custom sidecar Container image.

    • Miscellaneous: It is the responsibility of the sidecar implementer to include any additional Kubernetes resources that might be needed by their sidecar. They have complete control and responsibility for any supporting components such as Secrets, ConfigMaps, etc.

  2. Sidecar Interface

    These instructions define the expected interface with the custom sidecar container and are required for it to function properly. While it is possible for the user to implement the sidecar in the language of their choice, Golang is the obvious go-to. To aid in that implementation the user can make use of the code in the custom package. Specifically there are constants defining the expected Host, Port, Path and Header values used in creating the sidecar's REST endpoints. Coding directly against these constants reduces the implementation effort, and is an easy way to stay current with updates to the eventing-kafka implementation. Also included is the TopicDetail struct which can be used when Unmarshalling the JSON body of the POST request.

    Specifically the sidecar is expected to expose the following endpoints to be called by the eventing-kafka AdminClient implementation...

    • Create ( POST http://localhost:8888/topics )
      • Endpoint
        • Protocol: HTTP
        • Method: POST
        • Host: localhost (SidecarHost Constant)
        • Port: 8888 (SidecarPort Constant)
        • Path: /topics (TopicsPath Constant)
        • Param: n/a
      • Request
        • Header: "Slug" (TopicNameHeader Constant) will contain the Topic Name.
        • Body: application/json TopicDetail (TopicDetail Struct)
          • numPartitions: int32
          • replicationFactor: int16
          • replicaAssignment: map[int32][]int32
          • configEntries: map[string]*string
      • Response
        • 2XX: Treated as success by eventing-kafka and mapped to Sarama.ErrNoError.
        • 3XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.
        • 4XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.
        • 409: Treated as "already exists" by eventing-kafka and mapped to Sarama.ErrTopicAlreadyExists.
        • 5XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.
    • Delete ( DELETE http://localhost:8888/topics/<topic-name> )
      • Endpoint
        • Protocol: HTTP
        • Method: DELETE
        • Host: localhost (SidecarHost Constant)
        • Port: 8888 (SidecarPort Constant)
        • Path: / (TopicsPath Constant)
        • Param: topic-name
      • Request
        • Header: n/a
        • Body: n/a
      • Response
        • 2XX: Treated as success by eventing-kafka and mapped to Sarama.ErrNoError.
        • 3XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.
        • 4XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.
        • 404: Treated as "not found" by eventing-kafka and mapped to Sarama.ErrUnknownTopicOrPartition.
        • 5XX: Treated as error by eventing-kafka and mapped to Sarama.ErrInvalidRequest.

Note - The 409 and 404 HTTP StatusCodes, and their corresponding Sarama Types, are an expected part of the normal operation of eventing-kafka, and your side-car should return them when encountering those scenarios (already exists, and already deleted).

Note - There is no authentication / security between the endpoints as all communication is entirely intra-Pod.