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Add JVM Checkpoint Restore documentation 

See gh-37975
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Sébastien Deleuze 2023-10-20 14:44:25 +02:00 committed by Moritz Halbritter
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spring-boot-project/spring-boot-docs/src/docs/asciidoc/deployment/efficient.adoc
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@ -65,3 +65,16 @@ It implies the following restrictions:
- Properties that change if a bean is created are not supported (for example, `@ConditionalOnProperty` and `.enable` properties).
To learn more about ahead-of-time processing, please see the <<native-image#native-image.introducing-graalvm-native-images.understanding-aot-processing,Understanding Spring Ahead-of-Time Processing section>>.
[[deployment.efficient.crac]]
=== Checkpoint and Restore With the JVM
https://wiki.openjdk.org/display/crac/Main[CRaC] is an OpenJDK project that defines a new Java API to allow you to checkpoint and restore an application on the HotSpot JVM. It is based on https://github.com/checkpoint-restore/criu[CRIU], a project that implements checkpoint/restore functionality on Linux.
The principle is the following: you start your application almost as usual but with a CRaC enabled version of the JDK like https://www.azul.com/downloads/?package=jdk-crac#zulu[the one provided by Azul]. Then at some point, potentially after some workloads that will make your JVM hot by executing all common code paths, you trigger a checkpoint using an API call, a `jcmd` command, an HTTP endpoint, or another mechanism.
A memory representation of the running JVM, including its warmness, is then serialized to disk, allowing a very fast restoration at a later point, potentially on another machine with a similar operating system and CPU architecture. The restored process retains all the capabilities of the HotSpot JVM, including further JIT optimizations at runtime.
Based on the foundations provided by Spring Framework, Spring Boot provides support for checkpointing and restoring your application, and manages out-of-the-box the lifecycle of resources such as socket, files and thread pools https://github.com/spring-projects/spring-checkpoint-restore-smoke-tests/blob/main/STATUS.adoc[on a limited scope]. Additional lifecycle management is expected for other dependencies and potentially for the application code dealing with such resources.
You can find more details about the 2 modes supported ("on demand checkpoint/restore of a running application" and "automatic checkpoint/restore at startup"), how to enable Project CRaC support and some guidelines in {spring-framework-docs}/integration/checkpoint-restore.html[the Spring Framework JVM Checkpoint Restore support documentation].