http-kafka Binding

Zilla runtime http-kafka binding.

http_kafka_proxy:
  type: http-kafka
  kind: proxy
  routes:
    - when:
        - method: GET
          path: /items
      exit: kafka_cache_client
      with:
        capability: fetch
        topic: items-snapshots
        merge:
          content-type: application/json
    - when:
        - method: GET
          path: /items/{id}
      exit: kafka_cache_client
      with:
        capability: fetch
        topic: items-snapshots
        filters:
          - key: ${params.id}
    - when:
        - method: PUT
          path: /items/{id}
        - method: GET
          path: /items/{id};cid={correlationId}
      exit: kafka_cache_client
      with:
        capability: produce
        topic: items-requests
        acks: leader_only
        key: ${params.id}
        reply-to: items-responses
        async:
          location: /items/${params.id};cid=${correlationId}

Summary

The proxy kind http-kafka binding adapts http request-response streams to kafka topic streams.

Fetch capability

Routes with fetch capability map http GET requests to a kafka log-compacted topic, supporting filtered retrieval of messages with a specific key, or unfiltered retrieval of all messages with distinct keys in the topic merged into a unified response.

Filtering can be performed by kafka message key, message headers, or a combination of both message key and headers, extracting the parameter values from the inbound http request path.

Status 200 http responses include an etag header that can be used with if-none-match for subsequent conditional GET requests to check for updates. Rather than polling, http requests can also include the prefer: wait=N header to wait a maximum of N seconds before responding with 304 if not modified. When a new message arrives in the topic that would modify the response, then all prefer: wait=N clients receive the response immediately.

Produce capability

Routes with produce capability map any http request-response to a correlated pair of kafka messages. The http request message is sent to a requests topic, with a zilla:correlation-id header. When the request message received and processed by the kafka requests topic consumer, it produces a response message to the responses topic, with the same zilla:correlation-id header to correlate the response.

Requests including an idempotency-key http header can be replayed and safely receive the same response. This requires the kafka consumer to detect and ignore the duplicate request with the same idempotency-key and zilla:correlation-id.

Specifying async allows clients to include a prefer: respond-async header in the http request to receive 202 Accepted response with location response header.

A corresponding routes[].when object with matching GET method and location path is also required for follow up GET requests to return the same response as would have been returned if prefer: respond-async request header had been omitted.

Configuration

Properties

• kind*
• options
  • options.idempotency
    • idempotency.header
  • options.correlation
    • correlation.headers
    • headers.reply-to
    • headers.correlation-id
• routes
• routes[].guarded
• routes[].when
  • when[].method
  • when[].path
• routes[].exit*
• routes[].with
• with.capability (fetch)
  • with.topic
  • with.filters
    • filters[].key
    • filters[].headers
  • with.merge
    • merge.content-type
    • merge.patch
    • patch.initial
    • patch.path
• with.capability (produce)
  • with.topic
  • with.acks
  • with.key
  • with.overrides
  • with.reply-to
  • with.async

* required

kind*

enum [ "proxy" ]

Behave as an http-kafka proxy.

kind: proxy

options

object

http-kafka-specific options for adapting http request-response streams to kafka topic streams.

options:
  idempotency:
    header: idempotency-key
  correlation:
    headers:
      reply-to: zilla:reply-to
      correlation-id: zilla:correlation-id

options.idempotency

object

HTTP request header used to specify the idempotency key when adapting http request-response streams to kafka topic streams.

idempotency.header

string | Default: "idempotency-key"

HTTP request header name for idempotency key.

options.correlation

object

Kafka request message headers injected when adapting http request-response streams to kafka topic streams.

correlation.headers

object

Kafka request message reply to and correlation id header names injected when adapting http request-response streams to kafka topic streams.

headers.reply-to

string | Default: "zilla:reply-to"

Kafka header name for reply-to topic.

headers.correlation-id

string | Default: "zilla:correlation-id"

Kafka header name for request-response correlation identifier.

routes

array of object

Conditional http-kafka-specific routes for adapting http request-response streams to kafka topic streams.

Correlated Request-Response route:

routes:
  - when:
      - method: PUT
        path: /items/{id}
      - method: GET
        path: /items/{id};cid={correlationId}
    exit: kafka_cache_client
    with:
      capability: produce
      topic: items-requests
      acks: leader_only
      key: ${params.id}
      reply-to: items-responses
      async:
        location: /items/${params.id};cid=${correlationId}

Single topic CRUD routes:

routes:
  - when:
      - method: POST
        path: /items
    exit: kafka_cache_client
    with:
      capability: produce
      topic: items-crud
      key: ${idempotencyKey}
  - when:
      - method: GET
        path: /items
    exit: kafka_cache_client
    with:
      capability: fetch
      topic: items-snapshots
      merge:
        content-type: application/json
  - when:
      - method: GET
        path: /items/{id}
    exit: kafka_cache_client
    with:
      capability: fetch
      topic: items-snapshots
      filters:
        - key: ${params.id}
  - when:
      - path: /items/{id}
    exit: kafka_cache_client
    with:
      capability: produce
      topic: items-crud
      key: ${params.id}

routes[].guarded

object as named map of string:string array

Roles required by named guard.

routes:
  - guarded:
      test:
        - read:items

routes[].when

array of object

List of conditions (any match) to match this route when adapting http request-response streams to kafka topic streams.
Read more: When a route matches

routes:
  - when:
      - method: GET
        path: /items/{id};cid={correlationId}

when[].method

string

HTTP Method, such as GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, TRACE, PATCH.

when[].path

string

Path with optional embedded parameter names, such as /{topic}.

routes[].exit*

string

Default exit binding when no conditional routes are viable.

routes:
  - when:
    ...
    exit: kafka_cache_client

routes[].with

oneOf: Fetch | Produce

Defines the route with the Fetch capability.

with:
  capability: fetch

Defines the route with the Produce capability.

with:
  capability: produce

with.capability (fetch)

object

Kafka parameters for matched route when adapting http request-response streams to kafka topic fetch streams.

with:
  capability: fetch
  topic: items-snapshots
  filters:
    - key: ${params.id}
  merge:
    content-type: application/json
    patch:
      initial: "[]"
      path: /-

with.topic

string

Topic name, optionally referencing path parameter such as ${params.topic}.

with.filters

array of object

List of criteria (any match) to this filter. Kafka filters for matched route when adapting http request-response streams to kafka topic fetch streams. All specified headers and key must match for the combined criteria to match.

filters[].key

string

Message key, optionally referencing path parameter such as ${params.key}.

filters[].headers

object

Message headers, with value optionally referencing path parameter such as ${params.headerX}.

with.merge

object

Merge multiple Kafka messages into a unified HTTP response. Kafka merge configuration for matched route when adapting http request-response streams to kafka topic streams where all messages are fetched and must be merged into a unified http response.

merge.content-type

const "application/json"

Content type of merged HTTP response.

merge.patch

object

Describes how to patch initial HTTP response to include one or more Kafka messages in unified HTTP response.

• patch (application/json)

  Kafka merge patch configuration for matched route when adapting http request-response streams to kafka topic streams where all messages are fetched and must be merged into a unified http response.

patch.initial

string

Initial JSON value.

patch.path

const "/-"

JSON Patch path to include each Kafka message in unified HTTP response.

with.capability (produce)

object

Kafka parameters for matched route when adapting http request-response streams to kafka topic produce streams.

with:
  capability: produce
  topic: items-requests
  acks: leader_only
  key: ${params.id}
  reply-to: items-responses
  async:
    location: /items/${params.id};cid=${correlationId}

with.topic

string

Kafka topic name, optionally referencing path parameter such as ${params.topic}.

with.acks

enum [ "none", "leader_only", "in_sync_replicas" ] | Default: "in_sync_replicas"

Kafka acknowledgement mode

with.key

string

Kafka message key, optionally referencing path parameter such as ${params.id}.

with.overrides

object

Kafka message headers, with values optionally referencing path parameter.

with.reply-to

string

Kafka reply-to topic name.

with.async

object

Allows an HTTP response to be retrieved asynchronously

async.location

string

Path where the async result can be fetched, with values optionally referencing path parameter or ${correlationId}.

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* required