An absence of local states

In traditional architectures, because the code is guaranteed to execute in a single runtime, it is taken for granted that it is possible to chain or pipe output from one component to another. This is called a local state. Because serverless systems are in fact ephemeral computational units, it is impossible to pass the local state created or mutated as a part of the computation to downstream functions or components without storing it in a temporary datastore.

It is important to note that this is not necessarily a drawback, as modern systems are recommended to be stateless, and should share nothing. However, it takes a significant mindset shift, especially for new serverless adopters.

For example, with the AuthN of REST API, created using AWS Lambda, creating sticky sessions (like one would in a traditional web application) is impossible. AuthN is achieved by using bearer authentication. The clients are identified by tokens, which are issued for the first time and are subsequently sent in every request. Such tokens have to be stored in read and write optimized datastores, like Redis. These tokens can then be accessed by the ephemeral functions by performing a simple lookup. This is a simple example to eliminate the need of using local state.