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asyncapi.http.kafka.proxy

In this guide, you create Kafka topics and use Zilla to implement the common Petstore example where requests are proxied to Kafka. Zilla is implementing the REST endpoints defined in an AsyncAPI 3.x spec and proxying them onto Kafka topics defined in an AsyncAPI 3.x spec based on the operations defined in each spec.

Running locally

This example can be run using Docker compose or Kubernetes. The setup scripts are in the compose and helm folders respectively and work the same way.

You will need a running kafka broker. To start one locally you will find instructions in the kafka.broker folder. Alternatively you can use the redpanda.broker folder.

Setup

Whether you chose compose or helm, the setup.sh script will:

  • create the necessary kafka topics
  • create the Petstore API at http://localhost:7114
./setup.sh

Using this example

Synchronous APIs

The /pet endpoint proxies to Kafka synchronously meaning they will behave like a normal rest endpoint where the message persists on a kafka topics.

Create a pet using the /pets endpoint in the implemented API.

curl -v --location 'http://localhost:7114/pets' \
--header 'Content-Type: application/json' \
--data '{
  "name": "Rocky",
  "id": 1
}'

output:

*   Trying 127.0.0.1:7114...
* Connected to localhost (127.0.0.1) port 7114 (#0)
> POST /pets HTTP/1.1
> Host: localhost:7114
> User-Agent: curl/7.88.1
> Accept: */*
> Content-Type: application/json
> Content-Length: 32
>
< HTTP/1.1 204 No Content
< Access-Control-Allow-Origin: *
<

List all the pets using GET request for the /pets endpoint

curl -v --location 'http://localhost:7114/pets' \
--header 'Accept: application/json'

output:

*   Trying 127.0.0.1:7114...
* Connected to localhost (127.0.0.1) port 7114 (#0)
> GET /pets HTTP/1.1
> Host: localhost:7114
> User-Agent: curl/7.88.1
> Accept: application/json
>
< HTTP/1.1 200 OK
< Content-Length: 32
< Content-Type: application/json
< Etag: AQIAAg==
< Access-Control-Allow-Origin: *
< Access-Control-Expose-Headers: *
<
{
  "name": "Rocky",
  "id": 1
}

Asynchronous APIs

The /customer endpoint is an asynchronous endpoint meaning it will success with a 202 ACCEPTED response and include a Location header that will include the correlation id used in the /customer;cid={correlationId} endpoint.

  • The petstore-customers Kafka topic will have all the pending customer object you posted with a zilla:correlation-id header on the kafka message.
  • The petstore-verified-customers Kafka topic will have all the verified customers and will need to include a matching zilla:correlation-id header to align with the message on the initial topic.

Create a non-verified customer using a POST request for the /customer endpoint

curl -v --location --globoff 'http://localhost:7114/customer' \
--header 'Prefer: respond-async' \
--header 'Content-Type: application/json' \
--data '{
    "id": 200000,
    "username": "fehguy",
    "status": "pending",
    "address": [
        {
            "street": "437 Lytton",
            "city": "Palo Alto",
            "state": "CA",
            "zip": "94301"
        }
    ]
}'

output:

*   Trying 127.0.0.1:7114...
* Connected to localhost (127.0.0.1) port 7114 (#0)
> POST /customer HTTP/1.1
> Host: localhost:7114
> User-Agent: curl/7.88.1
> Accept: */*
> Prefer: respond-async
> Content-Type: application/json
> Content-Length: 238
>
< HTTP/1.1 202 Accepted
< Content-Length: 0
< Location: /customer;cid={correlationId}
< Access-Control-Allow-Origin: *
< Access-Control-Expose-Headers: *
<

Copy the location, and create a GET async request using the location as the path. Note that the response will not return until you complete the following step to produce the response with kcat.

curl -v --location 'http://localhost:7114/customer;cid={correlationId}' \
--header 'Prefer: wait=1902418' \
--header 'Accept: application/json'

output:

*   Trying 127.0.0.1:7114...
* Connected to localhost (127.0.0.1) port 7114 (#0)
> GET /customer;cid=d9037ed5-a073-4a21-932d-2392a707800f-badc2e5c2abc25956e9d23d897d5db85 HTTP/1.1
> Host: localhost:7114
> User-Agent: curl/7.88.1
> Prefer: wait=1902418
> Accept: application/json
>
< HTTP/1.1 200 OK
< Content-Length: 135
< Access-Control-Allow-Origin: *
<
{"id":200000,"username":"fehguy","status":"approved","address":[{"street":"437 Lytton","city":"Palo Alto","state":"CA","zip":"94301"}]}%

Using kcat and the copied correlation-id produce the correlated message:

echo '{"id":200000,"username":"fehguy","status":"approved","address":[{"street":"437 Lytton","city":"Palo Alto","state":"CA","zip":"94301"}]}' | \
    kcat -P \
         -b localhost:29092 \
         -k "c234d09b-2fdf-4538-9d31-27c8e2912d4e" \
         -t petstore-verified-customers \
         -H "zilla:correlation-id={correlationId}"

Teardown

The teardown.sh script will remove any resources created.

./teardown.sh