Serverless Messenger (TM-Pro dev assignment)

Service Requirements:

Build a message delivery feature in AWS that can send messages to users and also keep track of what has been sent.

• Create an API to post a message which can be delivered to a recipient via SMS/email and keep a record of it
• Create an API to retrieve the messages sent to a particular recipient

Prerequisites

• Sending SMS messages with SNS have some limitations

• Sending Email messages with SES also have some limitations

Architecture diagram:

DynamoDB table design

Access patterns

Access pattern	Target	Parameters	Notes
Get messages	Main table	- to	Retrieve the messages sent to a particular recipient

Table design

Entity	PK	SK
Message	MESSAGE#<to>	MESSAGE#<messageId>

Security:

• DynamoDB encryption at rest enabled: Server-side KMS encryption with a master key managed by AWS
• SNS encryption of data in transit: "aws:SecureTransport": "true" policy condition
• SES encryption of data in transit: "aws:SecureTransport": "true" policy condition
• AppSync GraphQL API_KEY Authorization

Preparations and deployment

• Setup deployment properties in bin/serverless-messenger.ts file;

Property	Example values	Meaning
STAGE	'dev' / 'stage' / 'prod'	Prefix for all created resources
SNS_REGION	'eu-central-1' / etc...	SNS service region
SES_REGION	'eu-central-1' / etc...	SES service region
DEFAULT_EMAIL_FROM	'no-reply@example.com'	Default from address for outgoing email messages

• CDK deployment

# Bootstrap cdk environment
cdk bootstrap --profile <AWS_PROFILE_NAME>

# Deploy stack
cdk deploy --all --profile <AWS_PROFILE_NAME>

• Get endpoint url and API Key

cdk deploy command will provide you GraphQL endpoint URL and API Key value:

 ✅  ServerlessMessengerStackdev

✨  Deployment time: 100.1s

Outputs:
ServerlessMessengerStackdev.serverlessmessengerapikeyvaluedev = <API_KEY_VALUE>
ServerlessMessengerStackdev.serverlessmessengergraphqlurldev = https://<API_ID>.appsync-api.eu-central-1.amazonaws.com/graphql

✨  Total time: 119.98s

Usage

Authorization header

Include authorization header into your requests to GraphQL endpoint:

"x-api-key": " <API_KEY_VALUE>"

Send Email

Example request:

mutation sendMessage($input: MessageInput!) {
    sendMessage(input: $input) {
        to
        from
        body
        deliveryMethod
        deliveryStatus
        recipientId
        senderId
    }
}

Variables:

{
    "input": {
        "to": "<TO_EMAIL>",
        "subject": "Message",
        "body": "Hello world",
        "deliveryMethod": "EMAIL"
    }
}

Example response:

{
    "data": {
        "sendMessage": {
            "to": "<TO_EMAIL>",
            "from": "<DEFAULT_FROM_EMAIL>",
            "subject": "Message",
            "body": "Hello world",
            "deliveryMethod": "EMAIL",
            "deliveryStatus": "ACCEPTED",
            "recipientId": null,
            "senderId": null
        }
    }
}

Send SMS

Example request:

mutation sendMessage($input: MessageInput!) {
    sendMessage(input: $input) {
        to
        body
        deliveryMethod
        deliveryStatus
        recipientId
        senderId
    }
}

Variables:

{
    "input": {
        "to": "<TO_PHONE_NUMBER>",
        "body": "Hello world",
        "deliveryMethod": "SMS"
    }
}

Example response:

{
    "data": {
        "sendMessage": {
            "to": "<TO_PHONE_NUMBER>",
            "body": "Hello world",
            "deliveryMethod": "SMS",
            "deliveryStatus": "ACCEPTED",
            "recipientId": null,
            "senderId": null
        }
    }
}

Retrieve the messages sent to a particular recipient

Example request:

query getMessages($filter: MessageFilter!, $first: Int, $after: String) {
    getMessages(filter: $filter, first: $first, after: $after) {
        data {
            id
            to
            body
            deliveryMethod
            deliveryStatus
            from
            recipientId
            senderId
        }
        pageInfo {
            hasNextPage
            endCursor
        }
    }
}

Variables:

{
    "filter": {
        "to": "<TO_EMAIL>"
    },
    "first": 2,
    "after": null
}

Example response:

{
    "data": {
        "getMessages": {
            "data": [
                {
                    "id": "MESSAGE#01G8NB4BN5NVP67PFG8TYNDMSW",
                    "to": "<TO_EMAIL>",
                    "from": "<DEFAULT_FROM_EMAIL>",
                    "body": "Hello world 1",
                    "deliveryMethod": "EMAIL",
                    "deliveryStatus": "ACCEPTED",
                    "recipientId": null,
                    "senderId": null
                },
                {
                    "id": "MESSAGE#01G8NBDZ6YMH5SCEQ1BGR3QTWG",
                    "to": "<TO_EMAIL>",
                    "from": "<DEFAULT_FROM_EMAIL>",
                    "body": "Hello world 2",
                    "deliveryMethod": "EMAIL",
                    "deliveryStatus": "ACCEPTED",
                    "recipientId": null,
                    "senderId": null
                }
            ],
            "pageInfo": {
                "hasNextPage": true,
                "endCursor": "MESSAGE#01G8NBDZ6YMH5SCEQ1BGR3QTWG"
            }
        }
    }
}

Limitations and room for improvement

• Service allows to store senderId and recipientId attributes of message, but has zero knowledge of SENDER entity, and does not allow to retrieve all messages by senderId (can be easily added using DynamoDB GSI with PK MESSAGE#<senderId>)
• Service is not checking delivery status of SMS messages, message ACCEPTED delivery status means that message is valid and accepted by SNS for delivery; However, the message might not be delivered for other reasons (e.g. sandbox limitations).