[AWS - DA] Lambda (ALB, Mult-values header, Edge, Async invocation, Event Source Mapping, Destination) PART 1

Lambda integration with ALB

• HTTP(s)
• Lambda function must be registered in a target group

ALB Multi-Header Values

If a client connect to ALB, we can config settings of ALB whether support Multi-Header Values.

For example, client send query parameters `?name=foo&name=bar` which will be converted to `name: [‘foo‘, ‘bar‘]`

When enable Multi-value headers: HTTP headers and query string parameters that are sent with multiple values are shown as arrays within the AWS Lambda event are response objects.

Ref: https://www.cnblogs.com/Answer1215/p/14844873.html

Lambda@Edge

You have deployed a CDN using CloudFront. You want to run a global AWS Lambda alongside with CDN.

Lambda@Edge allows you to

• Build more responsive applications
• You don‘t manage servers, Lambda is deplooyed globally
• Customize the CDN contetn

Lambda - Asynchronous Invocations

How it works?

For example, s3 trigger Lambda, it will put events into a Queue, Lambda will read from Queue max 3 times if need retry, then you will see multi logs in CloudWatch. After 3 times retry, will send to DLQ.

Return StatusCode for Asyn is 202.

Enable DLQ for Lambda, you also need to attach IAM policy

Event Source Mapping

Lambda need to poll from the source. Lambda function is invoked synchronouly.

• Kinesis Data Streams
• SQS & SQS FIFO queue
• DynamoDB Streams

• By Default, if you function return an error, the entire batch is reprocessed until the function succeeds, or the items in the batch expire.

Destination

On Lambda invoke success or failure, you can send data to another AWS service, such as SQS or Kinesis.

For example, you upload an image to S3, and trigger Lambda processing, on sucess send message to a SQS; on failure, send message to another SQS

• on success: you will see message in SQS right away
• on failure: becasue S3 inovke Lambda is async, if on failure, Lambda will retry 3 times, so you will not be able to see the SQS message right away, but should be able to see it after 4 mins.