AWS Lambda之间的同步

Question

I am using several AWS lambda functions (and multiple instances of the same ones) to access objects within AWS. Any information on thread safety of lambdas? While order of writing is not important (in my case), atomicity of read-modify-write is. Anyone came across proper/intended solution?

Answer 1

I came across this because I'm trying to achieve the same thing.

Problem: I have a cluster of state machines running in EC2 instances. Each invokes a Lambda asynchronously (InvocationType.Event). I want to run the lambda code each time but perform a downstream network call only once from within the lambda.

Solution: Using a DynamoDB table with a relatively low TTL, I perform a conditional put of an item with unique id generated from event data that will be the same across all lambda invocations for that unique event. Then, I only perform the downstream network call if the conditional put succeeds.

It's a distributed synchronization technique often used in distributed systems for "fail-fast" systems, just via a lambda.

Answer 2

A strict read-modify-write atomicity requires serialization of processing (maybe using locks etc.). This is not possible with Lambda.

What you can do is this: Write your requests into a SQS Queue and then use a single-threaded (or properly synchronized) piece of software on a single EC2 instance to process the queue entries.

The CAP theorem ( https://en.wikipedia.org/wiki/CAP_theorem ) says that this impacts your availability, because this process on a single EC2 instance by design becomes your single point of failure.

You could also use a RDS DB with transactions (or even DynamoDB with conditional writes/consistent reads).