CloudWatch Events (EventBridge) in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a CloudWatch Event rule targets a Lambda function with a dead-letter queue configured?

You have a CloudWatch Event rule that triggers a Lambda function. The Lambda function has a dead-letter queue (DLQ) configured. What is the behavior when the Lambda function invocation fails?

A The event is retried twice and then sent to the DLQ if still failing.

B The event is retried indefinitely until the Lambda function succeeds, ignoring the DLQ.

C The event is discarded immediately without sending to the DLQ or retrying.

D The failed event is sent to the DLQ for later analysis and the event is not retried automatically.

💡 Hint

Think about how Lambda handles failures with DLQ configured in asynchronous invocation.

When a Lambda function is invoked asynchronously by CloudWatch Events and it fails, Lambda retries the invocation twice (total of three attempts). If it still fails, the event is sent to the configured DLQ.

❓ Architecture

intermediate

Which architecture best ensures exactly-once processing of events using EventBridge and SQS?

You want to design an architecture using EventBridge and SQS to ensure that each event is processed exactly once by your application. Which setup achieves this?

A EventBridge rule sends events to an SQS FIFO queue, and the application reads from the queue with message deduplication enabled.

B EventBridge rule sends events to a standard SQS queue, and the application deletes messages after processing.

C EventBridge rule sends events directly to Lambda with retries enabled to ensure no event loss.

D EventBridge rule sends events to SNS topic which fans out to multiple SQS queues for parallel processing.

💡 Hint

Consider which SQS queue type supports deduplication and ordering to avoid duplicate processing.

SQS FIFO queues support exactly-once processing with message deduplication and ordering. Using EventBridge to send events to a FIFO queue ensures no duplicates and ordered processing.

❓ security

advanced

What IAM permission is required for an EventBridge rule to invoke a Lambda function?

To allow an EventBridge rule to invoke a Lambda function, which IAM permission must be granted?

A "events:PutEvents" permission granted to the Lambda function role.

B "lambda:InvokeFunction" permission granted to the EventBridge service principal on the Lambda function resource.

C "lambda:CreateEventSourceMapping" permission granted to the EventBridge rule.

D "events:InvokeFunction" permission granted to the Lambda function resource.

💡 Hint

Think about what permission allows a service to call a Lambda function.

EventBridge needs permission to invoke the Lambda function. This is done by granting the "lambda:InvokeFunction" permission to the EventBridge service principal on the Lambda function's resource policy.

❓ Configuration

advanced

Which EventBridge rule pattern matches events from EC2 instance state changes to 'stopped' or 'terminated'?

Choose the correct EventBridge event pattern JSON that matches EC2 instance state changes when the state is either 'stopped' or 'terminated'.

A

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": {"equals": ["stopped", "terminated"]}
  }
}

B

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": "stopped,terminated"
  }
}

C

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": ["stopped", "terminated"]
  }
}

D

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": ["stopped"],
    "state": ["terminated"]
  }
}

💡 Hint

Remember the syntax for matching multiple values in an array for a key in EventBridge event patterns.

EventBridge event patterns use arrays to match multiple values for a key. Option C correctly uses an array for the "state" key. Option C treats it as a string, A uses invalid syntax, and D repeats the same key twice which is invalid JSON.

✅ Best Practice

expert

What is the best practice to avoid event loss when using EventBridge with multiple targets?

You have an EventBridge rule with multiple targets including Lambda, SQS, and SNS. To avoid losing events if one target fails, what is the best practice?

A Configure EventBridge to batch events and send them only once per minute to reduce failures.

B Send events only to Lambda and rely on Lambda retries to handle failures for other services.

C Use a single SNS topic as the target and subscribe all services to it to centralize event delivery.

D Configure a dead-letter queue (DLQ) for each target and enable retry policies on the EventBridge rule.

💡 Hint

Think about how to handle failures per target and ensure events are not lost.

Configuring a DLQ for each target ensures failed events are captured for later processing. Enabling retry policies helps EventBridge retry failed deliveries. This combination avoids event loss across multiple targets.