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THIS PROJECT IS NO LONGER MAINTAINED!

This is an archived, read-only repository. Klarna is no longer using Kastle, and after 3 years of inactivity the decision has been made to also stop maintaining the project.

Kastle - Kafka REST proxy

Kastle is a REST interface to Kafka cluster for producers, powered by Brod, Cowboy and Erlang VM.

Kastle can handle both HTTP and HTTPS requests and supports mutual TLS authentication.

It can run behind proxy (e.g. nginx) but it's not a must, erlang vm handles concurrent connections and slow clients rather well.

Quick demo

  • Build Kastle (require Erlang/OTP 18.0, or later)

    make

  • Start Kastle (require Docker-compose)

    make test-env

  • Start Kastle (connect to your running kafka cluster)

    Edit kafka_endpoints etc. in rel/sys.config to point your kafka cluster, and run Kastle by make run

  • cURL examples (by default kastle listens on port 8092 for http and 8093 for https requests)

curl -v -X POST -H "Content-type: application/binary" \
                -H "Kafka-Key:the-key" \
                --data "the-value" \
                http://localhost:8092/rest/kafka/v0/test-topic/0

curl -v -X POST -H "Content-type: application/binary" \
                -H "Kafka-Key:the-key" \
                --data "the-value" \
                --key priv/ssl/client.key \
                --cert priv/ssl/client.crt \
                --cacert priv/ssl/ca.crt \
                https://localhost:8093/rest/kafka/v0/test-topic/0

Http request specs

Produce a message to a random partition of a specified topic:

POST <endpoint>/rest/kafka/v0/<topic>

Produces a message to a specified partition of a specified topic.

POST <endpoint>/rest/kafka/v0/<topic>/<partition>

HTTP headers/body

Request body structure depends on headers.

HTTP headers option #1

Content-Type: application/json

Request body should be a JSON object with 2 mandatory fields:

key:   User defined key for the producing message
value: Message value which will be produced to the topic of user choice yes

HTTP headers option #2

Content-Type: application/binary
Kafka-Key: <kafka-key-value>

Kafka-Key is an optional header, but if present its value is used as a key for kafka message as is The whole POST request body will be taken by kastle as a binary blob and produce as kafka-value to kafka.

Response status codes

On success, the HTTP status code in the response header is 204 No Content.

On client error, we return a JSON error object, if applicable, and the HTTP status as one of the following:

  • 400 Bad Request if invalid JSON
  • 400 Bad Content-Type header value, if non compliant Content-Type header
  • 404 Not Found if unidentified topic or partition
  • 415 Unsupported Media Type, if unsupported or no Content-Type header
  • 500 If internal server fault took place
  • 503 If Kafka cluster is unavailable

Response headers

Content-Type: application/json
Charset: utf-8

JSON error object

{"error" : "error description"}

Example:

{"error" : "partition not found"}

Health check

GET <endpoint>/ping

Kastle is Ops friendly

  • RPM spec is included
  • Dockerfile is included
  • All (well, most of them) config variables can be overriden via env variables

Build Kastle rpm package:

make rpm

RPM includes Erlang runtime, so nothing special is required on the target system.

After installing kastle rpm an operator can use /usr/bin/kastle to talk to the node.

To give an example, we use the script below in launch configuration to initialize an AWS instance.

Just replace company.com and s3 bucket/folder with your names.

#!/bin/bash -ex
NAME=kastle.company.com
CACERTFILE=/etc/ssl/certs/kastle-ca.crt
CERTFILE=/etc/ssl/certs/kastle.crt
KEYFILE=/etc/pki/tls/private/kastle.key
aws s3 cp s3://s3_bucket/s3_folder/certs/${NAME}/kastle-ca.crt ${CACERTFILE}
aws s3 cp s3://s3_bucket/s3_folder/certs/${NAME}/kastle.crt ${CERTFILE}
aws s3 cp s3://s3_bucket/s3_folder/certs/${NAME}/kastle.key ${KEYFILE}

sed -i "/^KASTLE_KAFKA_ENDPOINTS=/c\KASTLE_KAFKA_ENDPOINTS=kafka.company.com" /etc/sysconfig/kastle
sed -i "/^KASTLE_ENABLE_SSL=/c\KASTLE_ENABLE_SSL=true" /etc/sysconfig/kastle
sed -i "/^KASTLE_SSL_CACERTFILE=/c\KASTLE_SSL_CACERTFILE=${CACERTFILE}" /etc/sysconfig/kastle
sed -i "/^KASTLE_SSL_CERTFILE=/c\KASTLE_SSL_CERTFILE=${CERTFILE}" /etc/sysconfig/kastle
sed -i "/^KASTLE_SSL_KEYFILE=/c\KASTLE_SSL_KEYFILE=${KEYFILE}" /etc/sysconfig/kastle
sudo systemctl start kastle

One can also set KASTLE_SSL_CIPHERS variable to comma-separated list of preferred cipher suites.

Example of httpc to access kastle https endpoint

1> SSLOpts =[{verify,verify_peer},{certfile,"priv/ssl/client.crt"},{keyfile, "priv/ssl/client.key"},{cacertfile,"priv/ssl/ca.crt"}].
[{verify,verify_peer},
 {certfile,"priv/ssl/client.crt"},
 {keyfile,"priv/ssl/client.key"},
 {cacertfile,"priv/ssl/ca.crt"}]
2> URL="https://localhost:8093/rest/kafka/v0/test-topic/0".
"https://localhost:8093/rest/kafka/v0/test-topic/0"
3> ContentType = "application/binary".
"application/binary"
4> Headers = [{"Kafka-Key", "the-key"}].
[{"Kafka-Key","the-key"}]
5> application:ensure_all_started(ssl).
{ok,[crypto,asn1,public_key,ssl]}
6> application:start(inets).
ok
7> httpc:request(post, {URL, Headers, ContentType, <<"the value">>}, [{ssl, SSLOpts}], []).
{ok,{{"HTTP/1.1",204,"No Content"},
     [{"date","Fri, 03 Jun 2016 08:40:45 GMT"},
      {"server","Cowboy"},
      {"content-length","0"},
      {"content-type","application/json; charset=utf-8"}],
     []}}