# DMSEventsNotifications

This project contains source code and supporting files for a serverless application that you can deploy with the SAM CLI. It includes the following files and folders.

- dms_events_notification - Code for the application's Lambda function.
- events - Invocation events that you can use to invoke the function.
- tests - Unit tests for the application code. 
- template.yaml - A template that defines the application's AWS resources.

The application uses several AWS resources, including AWS Lambda functions and AWS SNS. These resources are defined in the `template.yaml` file in this project. You can update the template to add AWS resources through the same deployment process that updates your application code.

If you prefer to use an integrated development environment (IDE) to build and test your application, you can use the AWS Toolkit.

The AWS Toolkit is an open source plug-in for popular IDEs that uses the SAM CLI to build and deploy serverless applications on AWS. The AWS Toolkit also adds a simplified step-through debugging experience for Lambda function code. See the following links to get started.

* [CLion](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [GoLand](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [IntelliJ](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [WebStorm](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [Rider](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [PhpStorm](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [PyCharm](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [RubyMine](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [DataGrip](https://docs.aws.amazon.com/toolkit-for-jetbrains/latest/userguide/welcome.html)
* [VS Code](https://docs.aws.amazon.com/toolkit-for-vscode/latest/userguide/welcome.html)
* [Visual Studio](https://docs.aws.amazon.com/toolkit-for-visual-studio/latest/user-guide/welcome.html)

## Behind the logic in AWS Lambda function

The Lambda function acts as a mechanism to read the CloudWatch Logs that are sent by DMS Task and send SNS notifications to the subscribed SNS Topics. Here, we can walk-through the code logic running inside the Lambda function that is written in Python 3.9 runtime:

The CloudWatch Log trigger sends a message event to the Lambda function whenever a filter pattern, the one set in template.yaml parameter FilterPattern, is matched in the DMS error logs. This event is sent as a Base64-encoded .gzip file archive. To read the message data, it is first decoded and decompressed which reveals a JSON document containing the DMS task event details.

The JSON document is de-serialized to identify the DMS task, Replication Instance and the DMS task error message. These details help us form an email message body in order to notify user(s) on a specific DMS task with error. We then use this information to form a text that is published to a SNS Topic ARN using Python Boto3 SDK. The Lambda function identifies the SNS Topic ARN based on the environment variable snsARN set on the Lambda function. This environment variable is set automatically during the SAM deploy execution as it asks the user to specify the value for parameter pSNSTopicName they wish to publish the error messages.

In case an error arises during the Lambda execution, the Lambda error events are published to CloudWatch for troubleshooting. You can then review and debug the code as required. The Lambda function execution completes once the email message is sent successfully. The subscribed email addresses will then receive a message with the formulated text body from this function.

## Deploy the sample application

The Serverless Application Model Command Line Interface (SAM CLI) is an extension of the AWS CLI that adds functionality for building and testing Lambda applications. It uses Docker to run your functions in an Amazon Linux environment that matches Lambda. It can also emulate your application's build environment.

To use the SAM CLI, you need the following tools.

* SAM CLI - [Install the SAM CLI](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-install.html)
* [Python 3 installed](https://www.python.org/downloads/)
* Docker - [Install Docker community edition](https://hub.docker.com/search/?type=edition&offering=community)

To build and deploy your application for the first time, run the following in your shell:

```bash
sam build --use-container
sam deploy --guided
```

The first command will build the source of your application. The second command will package and deploy your application to AWS, with a series of prompts:

* **Stack Name**: The name of the stack to deploy to CloudFormation. This should be unique to your account and region, and a good starting point would be something matching your project name.
* **AWS Region**: The AWS region you want to deploy your app to.
* **Confirm changes before deploy**: If set to yes, any change sets will be shown to you before execution for manual review. If set to no, the AWS SAM CLI will automatically deploy application changes.
* **Allow SAM CLI IAM role creation**: Many AWS SAM templates, including this example, create AWS IAM roles required for the AWS Lambda function(s) included to access AWS services. By default, these are scoped down to minimum required permissions. To deploy an AWS CloudFormation stack which creates or modifies IAM roles, the `CAPABILITY_IAM` value for `capabilities` must be provided. If permission isn't provided through this prompt, to deploy this example you must explicitly pass `--capabilities CAPABILITY_IAM` to the `sam deploy` command.
* **Save arguments to samconfig.toml**: If set to yes, your choices will be saved to a configuration file inside the project, so that in the future you can just re-run `sam deploy` without parameters to deploy changes to your application.

## Use the SAM CLI to build and test locally

Build your application with the `sam build --use-container` command.

```bash
DMSEventsNotifications$ sam build --use-container
```

The SAM CLI installs dependencies defined in `dms_events_notification/requirements.txt`, creates a deployment package, and saves it in the `.aws-sam/build` folder.

Test a single function by invoking it directly with a test event. An event is a JSON document that represents the input that the function receives from the event source. Test events are included in the `events` folder in this project.

Run functions locally and invoke them with the `sam local invoke` command.

```bash
DMSEventsNotifications$ sam local invoke DMSLogReaderLambda --event events/event.json
```

The SAM CLI reads the application template to determine the CloudWatch logs and the functions that they invoke. The `Events` property on each function's definition includes the route and method for each path.

```yaml
      Events:
        DMSLogsTrigger:
          # More info about CloudWatch Logs Event Source: https://github.com/aws/serverless-application-model/blob/master/versions/2016-10-31.md#cloudwatchlogs
          Type: CloudWatchLogs
          Properties:
            LogGroupName: !Ref pDMSLogGroupName
            FilterPattern: suspended
```

## Add a resource to your application
The application template uses AWS Serverless Application Model (AWS SAM) to define application resources. AWS SAM is an extension of AWS CloudFormation with a simpler syntax for configuring common serverless application resources such as functions, triggers. For resources not included in [the SAM specification](https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md), you can use standard [AWS CloudFormation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-template-resource-type-ref.html) resource types.

## Fetch, tail, and filter Lambda function logs

To simplify troubleshooting, SAM CLI has a command called `sam logs`. `sam logs` lets you fetch logs generated by your deployed Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug.

`NOTE`: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

```bash
DMSEventsNotifications$ sam logs -n DMSLogReaderLambda --stack-name DMSEventsNotifications --tail
```

You can find more information and examples about filtering Lambda function logs in the [SAM CLI Documentation](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-logging.html).

## Tests

Tests are defined in the `tests` folder in this project. Use PIP to install the test dependencies and run tests.

```bash
DMSEventsNotifications$ pip install -r tests/requirements.txt --user
# unit test
DMSEventsNotifications$ python -m pytest tests/unit -v
# integration test, requiring deploying the stack first.
# Create the env variable AWS_SAM_STACK_NAME with the name of the stack we are testing
DMSEventsNotifications$ AWS_SAM_STACK_NAME=<stack-name> python -m pytest tests/integration -v
```

## Cleanup

To delete the sample application that you created, use the AWS CLI. Assuming you used your project name for the stack name, you can run the following:

```bash
aws cloudformation delete-stack --stack-name DMSEventsNotifications
```

## Resources

See the [AWS SAM developer guide](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/what-is-sam.html) for an introduction to SAM specification, the SAM CLI, and serverless application concepts.

Next, you can use AWS Serverless Application Repository to deploy ready to use Apps and learn how authors developed their applications: [AWS Serverless Application Repository main page](https://aws.amazon.com/serverless/serverlessrepo/)

## Security

See [CONTRIBUTING](CONTRIBUTING.md#security-issue-notifications) for more information.

## License

This library is licensed under the MIT-0 License. See the [LICENSE](LICENSE.md) file.