SynkedUp.AwsMessaging 1.1.9

SynkedUp.AwsMessaging

A library for doing fan-out messaging using SNS topics and SQS queues in AWS according to our messaging conventions:

• Topics are named: {environment}_{publisher}_{event}_v{version}
  • Example: p_monolith_customer-updated_v1
• Queues are named: {topic}_{subscriber}_{process}
  • Example: p_monolith_customer-updated_v1_monolith_listener
• Queues are subscribed to the corresponding SNS topic
• Dead letter queues are created for each subscribing queue, with the name: {queue}_dl

AWS Credentials

This library is set up to interact with AWS using the AWSSDK.Extensions.NETCore.Setup package and automatically connect using configuration values and your ~/.aws credential configuration. Note the call to AddDefaultAWSOptions in the configuration steps below.

Publishing Messages

Configuration

Before you can use the IMessagePublisher, you must first set up your DI container:

SynkedUp.AwsMessaging.DependencyInjectionConfig.ConfigurePublisherServices(services);
services.AddDefaultAWSOptions(configuration.GetAWSOptions());

You must also register an instance of IPublisherConfig with the following fields:

• Environment - a short string (3 character maximum) specifying an environment
  • (e.g. "s" for staging; "p" for production; "dev" for development)

Publishing a Message

To publish a message, use an injected IMessagePublisher:

var topic = new Topic("monolith", "customer-updated", 1);
var message = new Message<CustomerUpdated>(topic, new TestData
{
    CustomerId = 123
});

await publisher.PublishAsync(message);

Each message is defined with by a topic and a body (a.k.a. payload). You can also optionally add a CorrelationId string on the Message<T>.

NOTE: The library does NOT automatically create topics. Message publishing will fail if the topic cannot be found. We recommend you create them as part of your IaC tooling (such as a terraform script).

Subscribing to Messages

Configuration

Before you can use the IMessageSubscriber, you must first set up your DI container:

SynkedUp.AwsMessaging.DependencyInjectionConfig.ConfigureSubscriberServices(services);
services.AddDefaultAWSOptions(configuration.GetAWSOptions());

You must also register an instance of ISubscriberConfig with the following fields:

• Environment - a short string (3 character maximum) specifying an environment
  • (e.g. "s" for staging; "p" for production; "dev" for development)
• MaxNumberOfMessages - the maximum number of messages to receive in a long-poll batch
• LongPollingSeconds - the number of seconds (up to 20) to wait per batch for SQS long-polling
• DeadLetterAfterAttempts - how many receive attempts before a message will be moved to the dead-letter queue
• VisibilityTimeoutSeconds - how many seconds before a message can be processed again

Subscribing

Subscribe to messages from a specific queue by using an injected IMessageSubscriber:

var topic = new Topic("monolith", "customer-updated", 1);
var subscription = new Subscription(topic, "monolith", "listener");
await subscriber.SubscribeAsync(subscription, cancellationToken, async (Message<CustomerUpdated> message) =>
{
    await DoSomethingWith(message);
});

The call to SubscribeAsync will fail if the SNS topic does not exist. If the SQS queue does not exist, it will be created along with a corresponding dead-letter queue.

Messages will continue to be received until the cancellationToken is marked canceled.

Reading from Dead-Letter Queues

You can also subscribe to messages from a dead-letter queue:

await subscriber.SubscribeToDeadLettersAsync(subscription, cancellationToken, async (string message) =>
{
    await DoSomethingWith(message);
});

Note that when you subscribe to a dead-letter queue, you will receive messages as their "raw" string values, since deserialization may have been why they failed to be processed originally.

Monitoring

The IMessageSubscriber emits events to inform you of message timings and any processing exceptions:

subscriber.OnException += (_, args) =>
{
    logger.warn(args.Exception, "Error processing events");
};
subscriber.OnMessageReceived += (_, args) =>
{
    recordProcessingTime(args.Subscription, args.ProcessingTime);
    recordRoundTripTime(args.Subscription, args.ReceivedAt - args.PublishedAt);
};

The IMessageProcessor also emits events so you can measure how long it is taking to send a message:

publisher.OnMessagePublished += (_, args) =>
{
    recordSendTime(args.Elapsed);
}

Unit Testing

When unit testing your classes which use this library, we recommend mocking the IMessageProcessor and IMessageSubscriber interfaces. We also provide a TestMessageBuilder which allows you to create messages with data which cannot be otherwise set on the message object:

var message = new TestMessageBuilder<SomeClass>()
    .WithPublishedAt(publishedAt)
    .WithReceivedAt(receivedAt)
    .Build(body);

Integration Tests

The integration tests in this repository expect to find a [profile synkedup] entry in your ~/.aws/config file. They also require 2 topics to be set up:

• dev_aws-messaging_test_v0
• dev_aws-messaging_dlq-test_v0

Version History

v1.0

Initial release.