At the recent re:Invent, AWS announced an update to its FaaS offering AWS Lambda with the Lambda SnapStart feature that reduces the cold start for Java Functions. 

AWS Lambda functions run inside a secure and isolated execution environment, and the lifecycle of each environment consists of three main phases: Init, Invoke, and Shutdown. The first phase, Init, bootstraps the runtime for the function and runs the function’s static code. 

For some languages like Java, runtimes in conjunction with frameworks such as Spring Boot, Quarkus, or Micronaut, the first phase Init can, according to the company, sometimes take as long as ten seconds (this includes dependency injection, compilation of the code for the function, and classpath component scanning). In addition, the static code might download some machine learning models, pre-compute some reference data, or establish network connections to other AWS services.

With Lambda SnapStart enabled for a function, publishing a new version of the function will trigger an optimization process. Jeff Barr, a chief evangelist at AWS, explains in the company’s news blog post:

The process launches your function and runs it through the entire Init phase. Then it takes an immutable, encrypted snapshot of the memory and disk state and caches it for reuse. When the function is subsequently invoked, the state is retrieved from the cache in chunks on an as-needed basis and used to populate the execution environment. This optimization makes invocation time faster and more predictable since creating a fresh execution environment no longer requires a dedicated Init phase.

Note that cached snapshots are deleted after 14 days of inactivity. In addition, AJ Stuyvenberg, a lead software engineer at Datadog, explains in a dev.to blog post:

This snapshot capability is powered by MicroVM Snapshot technology inside FireCracker, the underlying MicroVM framework used by Lambda as well as AWS Fargate. In practice, this means function handler code can start running with sub-second latency (up to 10x faster).

Source: https://dev.to/aws-builders/introducing-lambda-snapstart-46no

AWS states that Lambda SnapStart is ideal for synchronous APIs, interactive microservices, or data processing applications. 

Developers can activate Lambda SnapStart for new or existing Java-based Lambda functions running on Amazon Corretto 11 using the AWS Lambda API, AWS Management Console, AWS Command Line Interface (AWS CLI), AWS Cloud Formation, AWS Serverless Application Model (AWS SAM), AWS SDK, and AWS Cloud Development Kit (AWS CDK).

Regarding the support for Java, a respondent on a Reddit thread wrote:

This is a very cool new feature that sounds like it virtually eliminates cold starts.

A pity this is only Java, although I have hope this will come to the rest of the runtimes in due course. The implementation doesn't sound like it's really specific to the JVM.

The JVM is a good place to start, though, as it seems to be the place where cold starts hurt the most in Lambda.

Currently, Lambda SnapStart is available in the US East (Ohio, N. Virginia), US West (Oregon), Asia Pacific (Singapore, Sydney, Tokyo), and Europe (Frankfurt, Ireland, Stockholm) regions.