rainbow-fintech

An offline & mobile first neo-bank for underserved population.

Tech

Backend: NodeJS
IAAS:
1. Db: AWS Dynamo
2. Compute: AWS Lambda
3. Gateway: AWS API Gateway
4. Cache: AWS Elasticache
5. Broker: AWS SQS
CPAAS:
- Expensive, difficult, scalable (evaluated, but not used in this project):
  - Receiving:
    - textlocal +919220592205 NLLG7 (prefix)
    - ifttt (sms → webhook)
  - Sending:
    - twilio
    - gupshup
- Inexpensive, easy, very small scale (used in this project):
  - Android phone connected to internet, is installed with 2 specific apps, IFTTT & Pushbullet
  - Users send sms to this phone, an ifttt recipe triggers on incoming sms containing a keyword
  - Trigger reads sms content and POST's to Webhook which is hosted in AWS
  - Webhook processes the sms content & calls pushbullet api to send sms via same android phone
  - Inexpensive, since only sms sending charge as per carrier tariff
  - No need to dealing with CPAAS service providers
  - Caveats:
    - Android phone must be online all the time with IFTTT and Pushbullet running in the background

Db schema

table: userAccountIdMapping

phone (pk)
id

table: userAccount

id (pk)
name
phone
loc
pan
verification
balance
currentActive
createdAt

table: userTxn

txnId (pk)
firstParty
secondParty
requestType
money
status
createdAt
currentActive

table: floatingCashRequest indicates latest ask for floating cash request id

phone(pk)
id

table: userRequest

id (pk)
phone
requestType
where
money
otherAccount
status
extraInfo
currentActive
createdAt

table: userAccountLedger

id (pk)
phone
op
note
money
openingBalance
createdAt

table userBucket

phoneWithBucketName (pk)
balance

enums

const requestType = {
  register: 'register',
  collect: 'collect',
  pay: 'pay',
  transfer: 'transfer',
  seeSaved: 'seeSaved',
  sip: 'sip',
  bucket: 'bucket',
  findDeposit: 'findDeposit',
  findWithdraw: 'findWithdraw'
}

const txnStatus = {
  created: 'created',
  success: 'success',
  failed: 'failed',
}

const op = {
    debit: 'debit',
    credit: 'credit'
}

event schema

Message received from SQS

{
    "Records": [
        {
            "messageId": "315f83aa-e7f5-4cab-ab7a-08ebed382643",
            "receiptHandle": "AQEB9RDP/7wzhKAyAvKcPsj4ZIiP0lT2v7rUEHS3NdY9NUcl3c/MYrUxx/A+G95BCMxSbbvQlHr5/aqREd2fR7jlAljH+Tco+9yJpWD5m+2zlJL5eZ0lthD/Iu2fXTS7CoibGe9OXygVjtpprk5Rw6npGDSLm2g7XFnH9WQUS7Ff1arQF3QlAu300XTv8nvJVEn7ME2eUrp/y1lIQYQUamULE2tj1gEoC2aXKJx6D/nlV0UR3a9LxFgWQ43AGenzKjWCWw+XwT7aaqys1Rl93NlQeEx+uHOfTdCBjlb8+Ef7Xb0=",
            "body": "{\"sender\":\"919439831236\",\"content\":\"NLLG7 FIND WITHDRAW 1250 DELHI\",\"inNumber\":\"919220592205\",\"submit\":\"Submit\",\"network\":\"\",\"email\":\"none\",\"keyword\":\"NLLG7\",\"comments\":\"FIND WITHDRAW 1250 DELHI\",\"credits\":\"10\",\"msgId\":\"8831460984\",\"rcvd\":\"2022-04-26 17:27:08\",\"firstname\":\"\",\"lastname\":\"\",\"custom1\":\"\",\"custom2\":\"\",\"custom3\":\"\"}",
            "attributes": {
                "ApproximateReceiveCount": "1",
                "SentTimestamp": "1650974230025",
                "SequenceNumber": "18869393476595952384",
                "MessageGroupId": "Group1",
                "SenderId": "AIDAXYDVU3NFEQC345T7T",
                "MessageDeduplicationId": "3df828ca-1c61-40ef-aa43-f09343c13b3b",
                "ApproximateFirstReceiveTimestamp": "1650974232040"
            },
            "messageAttributes": {},
            "md5OfBody": "d4cb092b27df4d5c194720c09f47e11c",
            "eventSource": "aws:sqs",
            "eventSourceARN": "arn:aws:sqs:ap-south-1:532822678346:smsReceivedQ.fifo",
            "awsRegion": "ap-south-1"
        }
    ]
}

Message body published to sqs

original payload parsed from textlocal

{
        "sender": "919439831236",
        "content": "NLLG7 TRANSFER 3000 9876543210",
        "inNumber": "919220592205",
        "submit": "Submit",
        "network": "",
        "email": "none",
        "keyword": "NLLG7",
        "comments": "TRANSFER 3000 9876543210",
        "credits": "10",
        "msgId": "8831346667",
        "rcvd": "2022-04-26 16:25:34",
        "firstname": "",
        "lastname": "",
        "custom1": "",
        "custom2": "",
        "custom3": ""
    }

Note: payload actually sent to sqs

{ 
  "sender": "919439831236", 
  "content": "rain balance"
}

Docs

Dynamodb document client
Setup awscli for deploy script deploy.sh:

python3 -m venv .venv
.venv/bin/pip install awscli

To build & deploy:

sink (receive incoming sms)

./deploy.sh sink

worker (process sms)

./deploy.sh worker

To build lambda layer

create directory structure:

mkdir -p aws-sdk-layer/nodejs
cd aws-sdk-layer/nodejs

Use amazon linux 2 compatible environment to install required packages:

docker run --entrypoint "" -v "$PWD":/var/task "public.ecr.aws/lambda/nodejs:14" /bin/sh -c "npm install aws-sdk redis node-fetch@2.6.7; exit"

zip it

zip -r ../package.zip ../

create layer

Name: <anything>
Upload zip
Runtimes: Node.js 14.x

Use the layer in lambda function. This prevents bundling node_modules with zip that is deployed to lambda. Reduces the lambda zip package size and prevents version conflicts with lambda preinstalled packages.

Note: If elasticache is in private subnet

Lambda function needs to be inside vpc and must be associated with privates subnets same as elasticache
AWS VPC endpoints needs to be setup for - SQS & DynamoDB, since requests for these services travels through internet
Environment variables (Key: Value), needs to be set for lambda functions:

ACCESS_KEY_ID:	---
QUEUE_URL:	https://---.fifo
REDIS_ENDPOINT:	redis://---.aps1.cache.amazonaws.com:6379
REGION:	ap-south-1
SECRET_ACCESS_KEY:	---

Modify config: timeout to 30seconds at least, Memory to 256mb
Add follwing policies to the role (not ideal setup, just a shotgun approach):

AWSLambdaBasicExecutionRole-64...ef	(already exist, add the remaining 👇)
AmazonSQSFullAccess
AmazonElastiCacheFullAccess
AmazonDynamoDBFullAccess
AWSLambdaDynamoDBExecutionRole
AdministratorAccess
AWSLambdaSQSQueueExecutionRole
AWSLambdaInvocation-DynamoDB
AWSLambdaVPCAccessExecutionRole

abhisekpadhi / rainbow-fintech

rainbow-fintech

Tech

Db schema

event schema

Docs

Tests checklist (manual)

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