When receiving events in Lambda from SNS the outer structure of the event will look somewhat like:
{ "Records": [...] }
In all the tutorials I have seen there has only ever been 1 record in the records field.
Is it safe to make the assumption that the "Records"-array will only ever contain 1 item?
Each SNS notification will contain not more than one message.
Refer Reliability section in SNS FAQ : https://aws.amazon.com/sns/faqs/
Q: Will a notification contain more than one message? No, all notification messages will contain a single published message.
Having said that, each lambda function trigger will have just a single record