First i have a question about the way Lambda works:

If it’s only triggered by 1 SQS queue and that queue now contains 100 messages, would it sequentially create and tear down 100 lambdas processes? Or would it do it in parallel?

My second question is the main one:
The job of my lambda is to request an access token (for an external service) that expires every hour and using it, perform some action on that external service.

Now, i want to be able to cache that token and only ask for it every 1 hour, instead of every time i make the request using the lambda.

Given the nature of how Lambda works, is there a way of doing it through code?
How can i make sure all Lambdas processes use the same access token?
(I know i can create a new Redis instance and make them all point to it, but i’m looking for a “simpler” solution)

You can stuff the token in the SSM parameter store. You can encrypt the value. Lambdas can check the last modified date on the value to monitor when expiration is pending and renew. No Redis instance to maintain, and the value would be encrypted.

https://docs.aws.amazon.com/systems-manager/latest/userguide/systems-manager-paramstore.html

You could also use DynamoDB for this. Lower overhead than Redis since it’s serverless. If you have a lot of concurrent Lambda, this may be preferable to SSM because you may run into rate limiting on the API. A little more work because you have to setup a DynamoDB table.

Another option would be to have a “parent” Lambda function that gets the API token and calls the “worker” Lambdas and passes the token as a parameter.