Redis Event Delivery

Event Delivery system to fan-out multiple requests or events to multiple destinations built on top of Redis. The system is based on scalable publisher-subscriber pattern and containerised using Docker.

Table of contents

• Features
• Installation
  • Docker deployment
  • Requirements for local development
• Design
  • Publish Event API
  • Successful Event
  • Failed Event

Features

1. Durability

Once API receives the event, it persists the data before performing any other actions making the event data secure and durable.

2. At-least-once delivery

Whenever failure occurs, the system will push to publish event data again until it gets at least one successful publish.

3. Retry backoff and limit

We have flexible MAX_RETRY limit to stop error prone events from blocking the queue.

We further have an Exponential backoff algorithm implemented for retry so it does not overload the Consumer.

$w = Base\ wait\ duration$
$n = Number\ of\ times\ publish\ event\ was\ tried$
$r = Small\ random\ delay\ for\ variance$

$backoff_delay = w \times 2^n \pm r$

4. Maintaining order

The events always maintain a FIFO order based on event_recieved_time and will always follow the same order even in case of failures.

5. Delivery Isolation

Current implementation does not support isolation, but is open to extension. Isolation can be achieved by separating channels to publish for each Comsumer, and scaling the database tables based on Consumer. This will make queues isolated and much faster in execution.

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Installation

Docker deployment

# We can modify image in docker-compose.yml to get live image from GitHub
# Or build local Doccker image like given below
docker build . --tag abhishekchd/redis-event-delivery

# Deploy the container to Docker
docker compose -f ./docker-compose.yml -p redis-event-delivery up -d
 
# Call API to verify if the app is up and running
curl --location --request POST 'http://localhost:8080/publish-event' \
--header 'Content-Type: application/json' \
--data '{
    "userId": "user-id-1",
    "payload": "Event payload"
}'

# Response from live server
$ Received event: Event(userId=user-id-1, payload=Event payload)

Requirements for local development

1. PostgresSQL 15
2. Redis server

Design

Redis Event Delivery System Design

Publish Event API

Send event payload through the Publish Event API using POST to securely transfer data.

POST /publish-event HTTP/1.1
Host: localhost:8080
Content-Type: application/json
{
    "userId": "<user-id>",
    "payload": "<Event Payload>"
}

Successful Event

After the event is successfully published, data is deleted from database permanently.

[INFO] i.g.a.r.scheduler.EventScheduler         : Event Watcher Running
[INFO] i.g.a.r.scheduler.EventScheduler         : Loaded event 7f000001-8a3c-1f0e-818a-3cef5b3f0000 from database
[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1f0e-818a-3cef5b3f0000 with delay of 502
[INFO] i.g.a.r.publisher.RedisEventPublisher    : Channel: sample-queue, Message: Event(userId=user-id-1, payload=Message from Postman)
[INFO] i.g.a.r.subscriber.EventSubscriber       : Received <Event(userId=user-id-1, payload=Message from Postman)>
[INFO] i.g.a.r.subscriber.EventSubscriber       : Processed Message <{"userId":"user-id-1","payload":"Message from Postman"}>
[INFO] i.g.a.r.scheduler.EventScheduler         : Event 7f000001-8a3c-1f0e-818a-3cef5b3f0000 successfully published in 0 retries

Failed Event

We have Scheduled Events with delay using backoff algorithm, and are always retried in FIFO order.

Event Faliure Logs

[INFO] i.g.a.r.scheduler.EventScheduler         : Event Watcher Running
[INFO] i.g.a.r.scheduler.EventScheduler         : Loaded event 7f000001-8a3c-1e16-818a-3cde32ad0000 from database
[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1e16-818a-3cde32ad0000 with delay of 508
[INFO] i.g.a.r.publisher.RedisEventPublisher    : Channel: sample-queue, Message: Event(userId=user-id-1, payload=Message from Postman)
[INFO] i.g.a.r.subscriber.EventSubscriber       : Received <Event(userId=user-id-1, payload=Message from Postman)>
[INFO] i.g.a.r.subscriber.EventSubscriber       : Processed Message <{"userId":"user-id-1","payload":"Message from Postman"}>
[INFO] i.g.a.r.scheduler.EventScheduler         : Event 7f000001-8a3c-1e16-818a-3cde32ad0000 failed - Failed to deliver. Pushing for retry.

Event retry using backoff algorithm and retry limit of 4

[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1e16-818a-3cde32ad0000 with delay of 1008
[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1e16-818a-3cde32ad0000 with delay of 2004
[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1e16-818a-3cde32ad0000 with delay of 3994
[INFO] i.g.a.r.scheduler.EventScheduler         : Scheduled event 7f000001-8a3c-1e16-818a-3cde32ad0000 with delay of 7997
[INFO] i.g.a.r.scheduler.EventScheduler         : Event 7f000001-8a3c-1e16-818a-3cde32ad0000 failed - Failed to deliver. Retry limit of 4 reached.