6.2.5. CoAP Kafka Connect - Coap

A Connector and Source to stream messages from a CoAP server and write them to a Kafka topic.

The Source supports:

  1. DTLS secure clients.
  2. Observable resources.

The Source Connector automatically converts the CoAP response into a Kafka Connect Struct to be store in Kafka as Avro or Json dependent on the Converters used in Connect. The schema can found here.

The key of the Struct message sent to Kafka is made from the source defined in the message, the resource on the CoAP server and the message id. Prerequisites

  • Apache Kafka
  • Kafka Connect Setup CoAP Setup

The connector uses Californium Java API under the hood. A resource is host at coap://californium.eclipse.org:5683. Copper, a FireFox browser addon is available so you can browse the server and resources.. This is an observable non confirmable resource. You can view messages via the browser addon by selecting the resource and clicking the observe button on the top menu. Source Connector QuickStart

We you start the Confluent Platform, Kafka Connect is started in distributed mode (confluent start). In this mode a Rest Endpoint on port 8083 is exposed to accept connector configurations. We developed Command Line Interface to make interacting with the Connect Rest API easier. The CLI can be found in the Stream Reactor download under the bin folder. Alternatively the Jar can be pulled from our GitHub releases page. Starting the Connector

Download, unpack and install the Stream Reactor and Confluent. Follow the instructions here if you haven’t already done so. All paths in the quickstart are based in the location you installed the Stream Reactor.

Once the Connect has started we can now use the kafka-connect-tools cli to post in our distributed properties file for MQTT. If you are using the dockers you will have to set the following environment variable to for the CLI to connect to the Rest API of Kafka Connect of your container.

export KAFKA_CONNECT_REST="http://myserver:myport"
➜  bin/connect-cli create coap-source < conf/coap-source.properties

#Connector name=`coap-source`
name = coap-source
tasks = 1
connector.class = com.datamountaineer.streamreactor.connect.coap.source.CoapSourceConnector
connect.coap.uri = coap://californium.eclipse.org:5683
connect.coap.kcql = INSERT INTO coap-topic SELECT * FROM obs-pumping-non
#task ids: 0

The coap-source.properties file defines:

  1. The name of the source.
  2. The name number of tasks.
  3. The class containing the connector.
  4. The uri of the CoAP Server and port to connect to.
  5. The KCQL routing querying.. This specifies the target topic and source resource on the CoAP server.

Use the Confluent CLI to view Connects logs.

# Get the logs from Connect
confluent log connect

# Follow logs from Connect
confluent log connect -f

We can use the CLI to check if the connector is up but you should be able to see this in logs as-well.

#check for running connectors with the CLI
➜ bin/connect-cli ps
    ____        __        __  ___                  __        _
   / __ \____ _/ /_____ _/  |/  /___  __  ______  / /_____ _(_)___  ___  ___  _____
  / / / / __ `/ __/ __ `/ /|_/ / __ \/ / / / __ \/ __/ __ `/ / __ \/ _ \/ _ \/ ___/
 / /_/ / /_/ / /_/ /_/ / /  / / /_/ / /_/ / / / / /_/ /_/ / / / / /  __/  __/ /
/_____/\__,_/\__/\__,_/_/  /_/\____/\__,_/_/ /_/\__/\__,_/_/_/ /_/\___/\___/_/
   ______                 _____
  / ____/___  ____ _____ / ___/____  __  _______________
 / /   / __ \/ __ `/ __ \\__ \/ __ \/ / / / ___/ ___/ _ \ By Andrew Stevenson
/ /___/ /_/ / /_/ / /_/ /__/ / /_/ / /_/ / /  / /__/  __/
\____/\____/\__,_/ .___/____/\____/\__,_/_/   \___/\___/
                    /_/ (com.datamountaineer.streamreactor.connect.coap.source.CoapSourceTask:54)
[2017-01-09 20:42:44,830] INFO CoapConfig values:
    connect.coap.uri = coap://californium.eclipse.org:5683
    connect.coap.port = 0
    connect.coap.truststore.pass = [hidden]
    connect.coap.cert.chain.key = client
    connect.coap.keystore.path =
    connect.coap.kcql = INSERT INTO coap-topic SELECT * FROM obs-pumping-non
    connect.coap.truststore.path =
    connect.coap.certs = []
    connect.coap.keystore.pass = [hidden]
    connect.coap.host = localhost
[2017-01-09 20:42:44,831] INFO Source task WorkerSourceTask{id=coap-source-0} finished initialization and start (org.apache.kafka.connect.runtime.WorkerSourceTask:138)
[2017-01-09 20:42:45,927] INFO Discovered resources /.well-known/core (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60)
[2017-01-09 20:42:45,927] INFO Discovered resources /large (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60)
[2017-01-09 20:42:45,928] INFO Discovered resources /large-create (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60)
[2017-01-09 20:42:45,928] INFO Discovered resources /large-post (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60)
[2017-01-09 20:42:45,928] INFO Discovered resources /large-separate (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60)
[2017-01-09 20:42:45,928] INFO Discovered resources /large-update (com.datamountaineer.streamreactor.connect.coap.source.CoapReader:60) Check for records in Kafka

Check for records in Kafka with the console consumer.

➜  bin/kafka-avro-console-consumer \
   --zookeeper localhost:2181 \
   --topic coap-topic \
{"message_id":{"int":4806},"type":{"string":"ACK"},"code":"4.04","raw_code":{"int":132},"rtt":{"long":35},"is_last":{"boolean":true},"is_notification":{"boolean":false},"source":{"string":"idvm-infk-mattern04.inf.ethz.ch:5683"},"destination":{"string":""},"timestamp":{"long":0},"token":{"string":"b24774e37c2314a4"},"is_duplicate":{"boolean":false},"is_confirmable":{"boolean":false},"is_rejected":{"boolean":false},"is_acknowledged":{"boolean":false},"is_canceled":{"boolean":false},"accept":{"int":-1},"block1":{"string":""},"block2":{"string":""},"content_format":{"int":-1},"etags":[],"location_path":{"string":""},"location_query":{"string":""},"max_age":{"long":60},"observe":null,"proxy_uri":null,"size_1":null,"size_2":null,"uri_host":null,"uri_port":null,"uri_path":{"string":""},"uri_query":{"string":""},"payload":{"string":""}} Features

  1. Secure DTLS client connection.
  2. Supports Observable resources to stream changes on a resource to Kafka.
  3. Routing of data via KCQL to topics.
  4. Automatic conversion of CoAP Response messages to Connect Structs. Kafka Connect Query Language

K afka C onnect Q uery L anguage found here GitHub repo allows for routing and mapping using a SQL like syntax, consolidating typically features in to one configuration option.

The CoAP Source supports the following:

INSERT INTO <topic> SELECT * FROM <resource>

No selection of fields on the CoAP message is support. All the message attributes are mapped to predefined Struct representing the CoAP response message. DTLS Secure connections

The Connector use the Californium Java API and for secure connections use the Scandium security module provided by Californium. Scandium (Sc) is an implementation of Datagram Transport Layer Security 1.2, also known as RFC 6347.

Please refer to the Californium certification repo page for more information.

The connector supports:

  1. SSL trust and key stores
  2. Public/Private PEM keys and PSK client/identity
  3. PSK Client Identity

The Sink will attempt secure connections in the following order if the URI schema of connect.coap.uri set to secure, i.e.``coaps``. If connect.coap.username is set PSK client identity authentication is used, if additional connect.coap.private.key.path Public/Private keys authentication will also be attempt. Otherwise SSL trust and key store.

    `openssl pkcs8 -in privatekey.pem -topk8 -nocrypt -out privatekey-pkcs8.pem`

Only cipher suites TLS_PSK_WITH_AES_128_CCM_8 and TLS_PSK_WITH_AES_128_CBC_SHA256 are currently supported.


The keystore, truststore, public and private files must be available on the local disk of the worker task.

Loading specific certificates can be achieved by providing a comma separated list for the connect.coap.certs configuration option. The certificate chain can be set by the connect.coap.cert.chain.key configuration option. Configurations

Config Description Type
connect.coap.uri Uri of the CoAP server string
connect.coap.kcql The KCQL statement to select and route resources to topics string

Optional Configurations

Config Description Type
connect.coap.port The port the DTLS connector will bind to on the Connector host. Default : 0 int
connect.coap.host The hostname the DTLS connector will bind to on the Connector host. Default : localhost string
connect.coap.username CoAP PSK identity string
connect.coap.password CoAP PSK secret password
connect.coap.public.key.file Path to the public key file for use in with PSK credentials string
connect.coap.keystore.path The path to the keystore string
connect.coap.keystore.pass The password of the key store. Default : rootPass string
connect.coap.truststore.path The path to the truststore string
connect.coap.truststore.pass The password of the trust store. Default : rootPass string
connect.coap.certs The certificates to load from the trust store list
connect.coap.cert.chain.key The key to use to get the certificate chain. Default ; client string
The number of events to take from the internal queue to batch
together to send to Kafka. Default : 100
connect.progress.enabled Enables the output for how many records have been processed. Default : false boolean
Path to the private key file for use in with PSK credentials
in PKCS8 rather than PKCS1. Use open SSL to convert
openssl pkcs8 -in privatekey.pem -topk8 -nocrypt -out privatekey-pkcs8.pem
Only cipher suites TLS_PSK_WITH_AES_128_CCM_8 and TLS_PSK_WITH_AES_128_CBC_SHA256 are currently supported
string Schema Evolution

The schema is fixed.

The following schema is used for the key:

Name Type
source Optional string
source_resource Optional String
message_id Optional int32

The following schema is used for the payload:

Name Type
message_id Optional int32
type Optional String
code Optional String
raw_code Optional int32
rtt Optional int64
is_last Optional boolean
is_notification Optional boolean
source Optional String
destination Optional String
timestamp Optional int64
token Optional String
is_duplicate Optional boolean
is_confirmable Optional boolean
is_rejected Optional boolean
is_acknowledged Optional boolean
is_canceled Optional boolean
accept Optional int32
block1 Optional String
block2 Optional String
content_format Optional int32
etags Array of Optional Strings
location_path Optional String
location_query Optional String
max_age Optional int64
observe Optional int32
proxy_uri Optional String
size_1 Optional String
size_2 Optional String
uri_host Optional String
uri_port Optional int32
uri_path Optional String
uri_query Optional String
payload Optional String Deployment Guidelines Distributed Mode

Connect, in production should be run in distributed mode.

  1. Install the Confluent Platform on each server that will form your Connect Cluster.
  2. Create a folder on the server called plugins/streamreactor/libs.
  3. Copy into the folder created in step 2 the required connector jars from the stream reactor download.
  4. Edit connect-avro-distributed.properties in the etc/schema-registry folder where you installed Confluent and uncomment the plugin.path option. Set it to the path you deployed the stream reactor connector jars in step 2.
  5. Start Connect, bin/connect-distributed etc/schema-registry/connect-avro-distributed.properties

Connect Workers are long running processes so set an init.d or systemctl service accordingly.

Connector configurations can then be push to any of the workers in the Cluster via the CLI or curl, if using the CLI remember to set the location of the Connect worker you are pushing to as it defaults to localhost.

export KAFKA_CONNECT_REST="http://myserver:myport" Kubernetes

Helm Charts are provided at our repo, add the repo to your Helm instance and install. We recommend using the Landscaper to manage Helm Values since typically each Connector instance has it’s own deployment.

Add the Helm charts to your Helm instance:

helm repo add datamountaineer https://datamountaineer.github.io/helm-charts/ TroubleShooting

Please review the FAQs and join our slack channel.