Overview
Let say you want to process images in background or any other task that requires heavy processing and you don’t want to tie this operation to any other core operation or service.
Suppose service A deals with users:
- Sign in
- Sign up
- Forgot password
- Profile update
- etc
Every time a user uploads an image to his profile you want to resize it and generate multiple thumbnails for multiple platforms or devices. You can do this operation under the same umbrella of service A but soon this business logic will grow up making our microservice a larger service.
So, you decide to separate this kind of operations to a new microservice (service B) but how you communicate with each other?
One option is to call the service directly but sounds you are tying bot services. Another option (here we go with this post) is to broadcast an event from service A called “profile updated”.
Now we have to see how service B is notified to start processing the image and here is where SNS and SQS come.
In the following example, I show you have to deploy an SNS topic that writes a message in an SQS queue. After that, you could have a Lambda function that is triggered by this queue but this is out of this scope.
The Cloudformation template
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
Sample SAM Template SNS and SQS
Parameters:
Environment:
Type: String
Description: example, staging
Resources:
MyQueue:
Type: AWS::SQS::Queue
Properties:
QueueName: !Sub "${Environment}-my-queue.fifo"
FifoQueue: true
MyTopic:
Type: AWS::SNS::Topic
Properties:
ContentBasedDeduplication: true
FifoTopic: true
Subscription:
- Endpoint:
Fn::GetAtt:
- MyQueue
- Arn
Protocol: sqs
TopicName: !Sub "${Environment}-my-topic.fifo"
MyQueuePolicy:
Type: AWS::SQS::QueuePolicy
DependsOn:
- MyQueue
Properties:
PolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: Allow
Principal:
Service:
- "events.amazonaws.com"
- "sqs.amazonaws.com"
- "sns.amazonaws.com"
Action:
- "sqs:SendMessage"
- "sqs:ReceiveMessage"
Resource:
Fn::GetAtt:
- MyQueue
- Arn
Condition:
ArnEquals:
aws:SourceArn:
Ref: MyTopic
Queues:
- Ref: MyQueue
Outputs:
MyTopicTopicARN:
Value:
Ref: MyTopic
MyQueue:
Value:
Fn::Join:
- " "
- - 'ARN:'
- Fn::GetAtt:
- MyQueue
- Arn
- 'URL:'
- Ref: MyQueue
Deploying using Sam
sam build
sam deploy --guided
