AWS Lambda

AWS Lambda is a service that provides you the option to run function written in .net core, node, python, java, etc to run on aws. AWS Lambda executes code only when needed and scales automatically. You pay only for the compute time you consume and no code when your code is not running, which is different than code running in Ec2 instance or ECS container. 

When a function is invoked, AWS lambda creates an instance and runs its handler method. While the first event is being processed, if the function is invoked again, and no instance is available, AWS lambda will create another instance. After processing the event the instance sticks around to process additional events. When a new instance is created, the response time increases which is called cold start. As more events come in, Lambda routes them to available instances and creates new instances as needed. Your function's concurrency is the number of instances serving requests at a given time. When the number of requests decreases, Lambda stops unused instances to free up scaling capacity for other functions. There is a limit to concurrency limit based on the region. When requests come in faster than your function can scale, or when your function is at maximum concurrency, additional requests fail with a throttling error.

You configure the amount of memory which will be available during execution. Similarly, you configure timeout which is the maximum time a function can run.  All AWS Lambda functions run securely inside a default system-managed Virtual Private Cloud (VPC) however you can configure it to run within custom VPC, subnet (use at least two subnets for high availability), and Security Group. When you enable a VPC, your Lambda function loses default internet access. If you require external internet access for your function, make sure that your security group allows outbound connections and that your VPC has a NAT gateway.

Lambda function and trigger (like API gateway) are the core component of AWS lambda. You specify the execution role is the IAM role that AWS Lambda assumes when it executes your function.