Welcome to PubSubApp break down

Technologies

• Nodejs(version > 8.0)

• Mocha

• Chai

• ExpressJs(Web Server)

• DB(Elasticsearch)

• eslint

File Structure

• APP content in app directory

• app

  • config

    • config

  • controllers

  • libraries

  • routes(Defines all endpoints to Curl in this App)

  • Dockerfile

  • docker-compose

  • services

  • start-server.sh(Entry Script)

Install all dependencies

npm install

Install ElasticSearch

• Install directly on your machine(Mac os, Windows, Linux):

• This approach will make the instance avaialble on localhost:9200 by default.

Start App

• At the base of the project, run the command below

npm run start

• Two servers will start at once. (publisher and subscriber)
• Publisher runs on Port 2300
• Subsciber(s) runs on Port 2400

Docker Approach

• install docker on your machine. Mac users could install Docker Desktop for ease of use and management.

docker pull docker.elastic.co/elasticsearch/elasticsearch:7.15.0

docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:7.15.0

• Be sure that elasticsearch is running before starting the app to avoid unnecessary error meesages.
• No need to do npm install if you will be using the docker-compose to run the app.

docker-compose build : To build the current state of the app.
docker-compose run : To run the app.

npm run test

• Add these to the .env file

export APP_BASE_URL=http://localhost
export SUBSCRIBER_PORT=2400
export PUBLISHER_PORT=2300
export ELASTIC_URL=http://localhost:9200

run source .env on your shell to make those variables available for use on your machine

• In this codebase, In order for the subscriber to receive the request, Http request using axios is made to a subscriber by the publisher.
• Since it's a demo, I have limited the number of subscribers to 2 to be able to manage the http calls.
• There are two subscriber urls over which the publisher can Ping the subscribers.
• On receiving an http request, a log is displayed to indicate that it has indeed been notified.
• The subscribers have been define in this app as routes that can be called via POST method.

• This is also represented by a route.
• A subscription request is made via an http call to the /subscribe/:topic route with a topic as a path param.
• Worth mentioning is that a topic can be subscribed to without a subscriberUrl. Hence I have made url not required in the request and instead it's defaulted to null.
• In the end, this route creates a relationship between the topic and the subscriberUrl.

• Represented by a route
• A publish request is made via an http call to /publish/:topic route with toic as a path param.
• The publisher notifies the subscriber endpoint which matches the topic;
• So if a record exists say topic = 'topic1', subscriberUrl = 'http://localhost:2400/alpha' (alpha) is a name of one of the subscriber's route(/alpha). A pblisher would only PING the exact subscribeUrl as indicated above(http://localhost:2400/alpha).
• Also if a topic belongs to more than one subscriberUrl say subscriberUrl = http://localhost:2400/beta (beta) is a name of another subscriberUrl and http://localhost:2400/alpha, two requests are made to each of the subscribers to Notify them.
• If a topic to be published to does not have a subscriberUrl associated to it, a successful response is still returned.

• Check out the test directory.

• checkout the postman collection here

===============================================================================================================

resource: "http://localhost:2300/subscribe/topic4"

_Sample POST request to create New Client

url: http://localhost:2400/beta

Required Fields url

_Sample Response

{
    "error": false,
    "message": "subscription to topic topic4 successful",
    "data": {
        "url": "http://localhost:2400/beta",
        "topic": "topic4"
    }
}

resource: "http://localhost:2300/publish/topic4"

_Sample POST request

message: "Hi publisher. gotcha"

Required Fields message

_Sample Response

{
    "error": false,
    "message": "Successfully Published to subscriber http://localhost:2400/beta"
}

Please check the postman collection for the complete details

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