Event tracking on Ethereum can be very painful when you are building a Scalable Dapp. Today we are going to look at Eventeum, developed by Kauri Team.

What is Eventeum?

Eventeum is an Ethereum event listener service that provides a bridge between your smart contracts and middleware layer. Events subscriptions can be registered dynamically, and on emission, a message containing the details of the events are broadcast onto a message bus (currently either Kafka or RabbitMQ) which can then be consumed by your backend services.

Eventeum is:

Dynamically Configurable — Eventeum exposes a REST api so that smart contract events can be dynamically subscribed / unsubscribed.

— Eventeum exposes a REST api so that smart contract events can be dynamically subscribed / unsubscribed. Highly Available — Eventeum instances communicate with each other to ensure that every instance is subscribed to the same collection of smart contract events.

— Eventeum instances communicate with each other to ensure that every instance is subscribed to the same collection of smart contract events. Resilient — Node failures are detected and event subscriptions will continue from the failure block once the node comes back online.

— Node failures are detected and event subscriptions will continue from the failure block once the node comes back online. Fork Tolerance — Eventeum can be configured to wait a certain amount of blocks before an event is considered ‘Confirmed’. If a fork occurs during this time, a message is broadcast to the network, allowing your services to react to the forked/removed event.[source]

Deploying Eventeum

Eventeum supports 3 broadcast mechanisms.

Kafka

HTTP Post

RabbitMQ

We will be using Kafka in our deployment.

To deploy Eventeum, you need these things:

Prerequisite

Java8

Maven

Mongo

Kafka

Zookeeper

Ethereum Node

Docker (optional)

You can deploy Eventeum with or without docker. To get started I’ll recommend docker all-in-one installation. It comes with all the dependencies mentioned above, though you still need to install Java8 and Maven (so install these first). I have installed both versions, with and without docker, but will mention docker all-in-one installation only as it is easy and you don’t need a lot of setups.

Installing Eventeum using Docker

To install Eventeum using Docker, you must have Docker and Docker-compose in your system. After installing them, follow below instructions

Checkout Eventeum Github Repo

After checking out the code, navigate to the root directory

$ cd /path/to/eventeum/

Compile, test and package the project

$ mvn clean package

All-in-one docker installation

$ cd server

$ docker-compose -f docker-compose.yml build

$ docker-compose -f docker-compose.yml up

Once installed you can see logs in docker terminal.

Note: You might need sudo depending on your docker installation.

Testing Eventeum

For this purpose, we will deploy a contract on our local parity node (already installed by Eventeum) and then will register an event subscription on Eventeum for Broadcasting via Kafka.

Deploy contract on Local Parity node

Let’s Deploy a contract we already made in our previous tutorial. To deploy CrudApp.sol contract we will use Remix IDE and Metamask.

Open Remix and add CurdApp.sol contract

Select proper compiler (0.4.23 in our case) and compile (Ignore warnings, if any 😃)

On Metamask Select Localhost:8545

In Remix, Go to Run Tab and select Web3 Provider in Environment and Deploy

That’s it you deployed the contract on your local Parity dev node.

Register Event

We need to now Register events, so Eventeum can listen to those events and broadcast them. Eventeum exposes rest APIs for this purpose, we will use them.

Register events API-

URL: /api/rest/v1/event-filter

Method: POST

{

"id": "event-identifier",

"contractAddress": "0x1fbBeeE6eC2B7B095fE3c5A572551b1e260Af4d2",

"eventSpecification": {

"eventName": "TestEvent",

"indexedParameterDefinitions": [

{"position": 0, "type": "UINT256"},

{"position": 1, "type": "ADDRESS"}],

"nonIndexedParameterDefinitions": [

{"position": 2, "type": "BYTES32"},

{"position": 3, "type": "STRING"}] },

"correlationIdStrategy": {

"type": "NON_INDEXED_PARAMETER",

"parameterIndex": 0 }

}

To make our life simple, we will simply do a curl call. As you can see below, we are using localhost:8060 (on which, Eventeum is running) and you need to add the address for your deployed smart contract from Remix. We are currently registering CountryEvent from our smart contract which gets emitted on insert transaction.



http://localhost:8060/api/rest/v1/event-filter \

-H 'Cache-Control: no-cache' \

-H 'Content-Type: application/json' \

-H 'Postman-Token: 616712a3-bf11-bbf5-b4ac-b82835779d51' \

-d '{

"id": "Country",

"contractAddress": "ENTER_YOUR_CONTRACT_ADDRESS_CHECK_IN_REMIX",

"eventSpecification": {

"eventName": "CountryEvent",

"nonIndexedParameterDefinitions": [

{"position": 0, "type": "STRING"},

{"position": 1, "type": "STRING"},

{"position": 2, "type": "UINT256"}] }

}' curl -X POST \-H 'Cache-Control: no-cache' \-H 'Content-Type: application/json' \-H 'Postman-Token: 616712a3-bf11-bbf5-b4ac-b82835779d51' \-d '{"id": "Country","contractAddress": "ENTER_YOUR_CONTRACT_ADDRESS_CHECK_IN_REMIX","eventSpecification": {"eventName": "CountryEvent","nonIndexedParameterDefinitions": [{"position": 0, "type": "STRING"},{"position": 1, "type": "STRING"},{"position": 2, "type": "UINT256"}] }}'

If registered successfully, you will get your ID (Country in our case) back as a response. Now Let’s do an insert transaction which will emit our CountryEvent . For this purpose, we’ll use Remix again, using remix, you can call your contract functions.

You can see our CrudApp.sol contract address and also functions exposed by the contract, you can call it from here only.

So Now, Let’s put these 3 things in insert function (“USA”, “Elizabeth Warren ”, 327946410), if everything went well, you will be able to see the transaction in Docker terminal.

Subscribing Eventeum events in NodeJs service

Now let’s subscribe Kafka events using a NodeJs service. This will help you to a clear picture about how you can use Eventeum with your application. For this follow these steps.



cd watcher

npm init

npm install

npm i kafka-node (

touch index.js mkdir watchercd watchernpm initnpm installnpm i kafka-node ( Kafka-nodejs client touch index.js

Now add below code in index.js

var kafka = require('kafka-node') const client = new kafka.KafkaClient({kafkaHost: 'localhost:9092'}); var kafka = require('kafka-node'),

Consumer = kafka.Consumer,

// client = new kafka.Client(),

consumer = new Consumer(

client,

[

{ topic: 'contract-events', partition: 0 }

],

{

autoCommit: false

}

); consumer.on('message', function (message) {

console.log(message);

});

You can run this using

nodejs index.js

To test this, again do an insert transaction using remix and you will able to see console output for the event.

As you can see we are using the topic as ‘contract-events’ , this is already inbuilt in Eventeum, to check all the topics defined by Eventeum.

bin/kafka-topics.sh --list --zookeeper localhost:2181

As you are using docker installation you need to go inside the docker and run the above command, though you need to change the /bin/kafka-topics.sh with actual installation path in docker. Eventeum already create below topics

__consumer_offsets

block-events

contract-events

filter-events

filter-events-dlteventeum

filter-events-erreventeum

filter-eventsnull

Here block-events track new block generations.

You can see more details here about Eventeum and learn more about it.

How to Use Eventeum on TestNet or MainNet?

To use Eventeum with Testnet or Mainnet you need to change Ethereum node URL in docker-compose.yml .

As I am facing problem with Infura’s eth_newBlockFilter api used by Eventeum, you can use QuikNode for this purpose.

QuikNode provides fast Ethereum nodes, combined with Eventeum you can monitor smart contract events reliably.

Register for a free account now!

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