Follower Maze

The Challenge

The challenge proposed here is to build a system which acts as a socket server, reading events from an event source and forwarding them when appropriate to user clients.

Clients will connect through TCP and use the simple protocol described in a section below. There will be two types of clients connecting to your server:

• One event source: It will send you a stream of events which may or may not require clients to be notified
• Many user clients: Each one representing a specific user, these wait for notifications for events which would be relevant to the user they represent

Events

There are five possible events. The table below describe payloads sent by the event source and what they represent:

Payload	Sequence #	Type	From User Id	To User Id
666|F|60|50	666	Follow	60	50
1|U|12|9	1	Unfollow	12	9
542532|B	542532	Broadcast	-	-
43|P|32|56	43	Private Msg	32	56
634|S|32	634	Status Update	32	-

Events may generate notifications for user clients. If there is a user client connected for them, these are the users to be informed for different event types:

• Follow: Only the To User Id should be notified
• Unfollow: No clients should be notified
• Broadcast: All connected user clients should be notified
• Private Message: Only the To User Id should be notified
• Status Update: All current followers of the From User ID should be notified

If there are no user client connected for a user, any notifications for them must be silently ignored. user clients expect to be notified of events in the correct order, regardless of the order in which the event source sent them.

Functional Specification

• The events will arrive out of order
• user clients expect to be notified of events in the correct order, regardless of the order in which the event source sent them.

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Architecture

Modules

Modules	Functionality
event-server	Event Server to receive event from event server program
clients	Client Server to accept/process client connections
commons	Commons functionality to be used acorss moduule like Kafka Messaging

You can run the full module from followermaze multi module java project

Steps to execute :

• Start Event Server -
  • Accept connections from event server on 9090
  • Push to Local Storage Periodically in bacthes

java -jar event-server/target/event-server-1.0-jar-with-dependencies.jar

• Start Client Server -
  • Accept client connections from event server on 9099
  • File consumer to listen from Local Storage & push to active client connections

java -jar clients/target/clients-1.0-jar-with-dependencies.jar

Property File Description

Server Config - config.properties

Property	Default	Description
server.host	localhost	Server Host
server.port	8080	Server Port
server.threads	10	Number of IO Threads for Server

File Config - file.proprties

Property	Default	Description
batch.file.path	/tmp	Local Storage Path to store batch event files
batch.size	100	Event Batch Size
batch.poll	5000	Polling time to check for new batch
max.retry	1	Retry attempt

Development References

We use Java7 NIO library to handle heavy file processing & Apache Commons Compress for GZIP Compression

• Paths - static methods that return a Path by converting a path string or URI.
• Files - static methods that operate on files, directories, or other types of files

More information about Paths module can be seen :

• Paths
• Files
• GZIP

Future Scope

• CPU Monitoring for JVM Optmization
• Test case coverage for Code Durability
• Dockerfile for full fledged shippable solution
• ELK integration to check stats of the events
• Distributed Tracing for event tracking