If Lambda has an always free tier why do we need the request and duration based pricing model?
AWS charges you when you exceed the 1 million. If you go to Lambda page it says "1,000,000 free requests per month" https://aws.amazon.com/lambda/
Free Tier: 1 million requests per month, 400,000 GB-seconds of compute time per month
$0.20 per 1 million requests thereafter, or $0.0000002 per request
400,000 GB-seconds per month free, up to 3.2 million seconds of compute time
$0.00001667 for every GB-second used thereafter