# notification-sender

A Java based AWS Lambda to send notifications via Amazon SNS (Amazon Simple Notification Service).


## Setup

### AWS Lambda

- Choose the latest version of the Java runtime
- The handler is `eu.ortlepp.notificationsender.NotificationHandler::handleRequest`
- The recommended timeout is 30 seconds
- The recommended RAM is 512 MB
- Two environment variables are required to run the Lambda:
  - `REGION` - the region of your SNS topic, e.g. `eu-central-1`
  - `ARN` - the ARN of your SNS topic, something like `arn:aws:sns:eu-central-1:123456789:Topic-Name`
- Create a function URL to trigger the Lambda
  - It is recommended to secure the function URL with IAM

### Amazon SNS

- Create a new topic; in the topic, create a subscription
  - Only e-mail subscriptions have been tested so far; other subscription types are untested


## Data

### Input (request)

HTTP POST to the function URL with JSON body:

```
{
  "messages" : ["first notification", "second notification"]
}
```

### Output (response)

The response is HTTP 200 with either

```
{
  "status" : "SUCCESS"
}
```

or

```
{
  "status" : "FAILED"
}
```

If the Lambda setup is improper, a timeout occurred, etc., the response is HTTP 500 from the AWS environment (not the Lambda itself).

### Result (SNS message)

If the messages array contains multiple messages, all elements of the messages array are combined into one SNS message. Empty messages (empty / whitespace-only string) are omitted.

Only one message:

```
my notification
```

Multiple messages:

```
1. Notification:
first notification

2. Notification:
second notification

```

SNS will automatically append an unsubscribe footer to each e-mail.


## Testing

You can use curl to trigger your Lambda:

```
curl -X POST -H "Content-Type: application/json" -d "{\"messages\":[\"my notification\"]}" --aws-sigv4 "aws:amz:eu-central-1:lambda" --user "ACCESS_KEY:SECRET_KEY" https://MY_FUNCTION_URL.lambda-url.eu-central-1.on.aws/
```


## Documentation

- [Building Lambda functions with Java](https://docs.aws.amazon.com/lambda/latest/dg/lambda-java.html)
- [How To Secure and Authenticate AWS Lambda Function URLs](https://www.rahulpnath.com/blog/how-to-secure-and-authenticate-lambda-function-urls/) & [FUNCTION URLs - Authenticating and Securing | AWS Lambda](https://www.youtube.com/watch?v=75EEaN-oBAg)
- [Amazon SNS examples using SDK for Java 2.x](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/java_sns_code_examples.html)