Sending message to SNS topic with 2 SQS subscriptions each with a lambda trigger results in empty queues

Question

so far I have set up an SNS topic with 2 SQS subscriptions to it. Each SQS has a lambda trigger associated with it.

When I send the message via SNS.publish like this to send message to the 2nd SQS subscription:

response = sns.publish(
    TopicArn='arn:aws:sns:us-west-2:234723472:test',
    Message=json.dumps({'default': json.dumps({"c": code, "event_type": queuename})}),
    MessageAttributes={'event_type':{'DataType':'String', 'StringValue':queuename}
)

the queue remains empty.

yet, when I send a message directly to the queue, the lambda trigger works. But the messages seem to be not getting past once sent to SNS. No errors is triggered. It's frustrating that SNS doesn't show a log of messages it received so I can't really debug things here.

What could I be missing?

I also tried with and without MessageStructure='json' above and it made no difference.

It's frustrating not knowing where the silent error is happening in AWS.

Tommy Tommy · Accepted Answer · 2019-06-07T22:15:35

I had the same problem. Please check if you have permissions set on SQS, so it can accept messages from the SNS.

Example:

# SQS Queue
MyQueue: 
  Type: AWS::SQS::Queue 
    Properties: 
      QueueName: MyQueue

# SNS Topic
MyTopic: 
  Type: AWS::SNS::Topic 
  Properties: 
    TopicName: MyTopic

# Topic Subscription 
MyTypicSubscription: 
  Type: AWS::SNS::Subscription 
    Properties: 
      Endpoint: !GetAtt MyQueue.Arn 
      Protocol: sqs 
      RawMessageDelivery: true 
      TopicArn: !Ref MyTopic 

#Permissions for SQS to receive SNS notifications 
MyQueuePermissions: 
  Type: AWS::SQS::QueuePolicy 
  Properties:  
    PolicyDocument: 
      Statement: 
        Effect: Allow 
        Principal: 
          AWS: '*' 
        Action: SQS:SendMessage 
        Resource: 
        - !GetAtt MyQueue.Arn 
        Condition: 
          ArnEquals:  
            aws:SourceArn: !Ref MyTopic 
    Queues:  
    - !Ref MyQueue

In console it looks like this:

The SNS service notifies its subscribers but "doesn't care" if the subscriber is available or not, hence no error message on SNS. Hope that helps!

Sending message to SNS topic with 2 SQS subscriptions each with a lambda trigger results in empty queues

1 Answers