Spring Boot graceful shutdown support

A feature still missing (since ever), this "draft" implementation is based on comments from issue #4657. Until the "official" solution arrives, feel free to test-drive and contribute.

What is graceful shutdown?

Is a way to don't upset your clients when you need to update your cluster. When the shutdown signal comes, you expect the instance to:

1. reject any new requests attempts (status 503), and
2. complete all pending requests (all requests that came before the shutdown signal).

Installation

This library has no transitive dependencies and assumes that you've already added all the desired spring-boot-starters dependencies.

If you're using Spring Boot 2.1, add

<dependency>
  <groupId>com.github.erdanielli</groupId>
  <artifactId>spring-boot-graceful-shutdown</artifactId>
  <version>2.1.1</version>
</dependency>

OR

for Spring Boot 2.0 projects, add

<dependency>
  <groupId>com.github.erdanielli</groupId>
  <artifactId>spring-boot-graceful-shutdown</artifactId>
  <version>2.0.0</version>
</dependency>

OR

for the ancient Spring Boot 1.5, add

<dependency>
  <groupId>com.github.erdanielli</groupId>
  <artifactId>spring-boot-graceful-shutdown</artifactId>
  <version>1.5.0</version>
</dependency>

AND YOU'RE DONE!

_{... unless you don't enjoy auto-configuration and prefer importing configurations by yourself, import com.github.erdanielli.boot.shutdown.undertow.UndertowGracefulShutdownConfiguration or com.github.erdanielli.boot.shutdown.tomcat.TomcatGracefulShutdownConfiguration}

Custom configurations

# Max duration to wait for pending requests to complete
# Duration values are only supported by Spring Boot 2.1.
# Previous versions must provide the value in milliseconds (30000)
server.shutdown-timeout=30s    

To enable/disable logging, fine-tune the logger com.github.erdanielli.boot.shutdown.GracefulShutdown

Limitations

1. Only servlet-based runtime is supported;
2. Undertow is preferred, Tomcat is also supported (see Caveats below);
3. No Jetty support yet.

Caveats

• Tomcat doesn't reject new requests with 503 yet. Instead, a 'connection reset by peer' error is returned only after the shutdown completes.

Further updates

Depends on the progress of issue #4657.

Acknowledgements

• All contributions on issue #4657
• Mohammad Nadeem's for his great DZone article that helped me putting this on Maven Central.