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Polish Liveness and Readiness support

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This commit moves the core Liveness and Readiness support to its own
`availability` package. We've made this a core concept independent of
Kubernetes.

Spring Boot now produces `LivenessStateChanged` and
`ReadinessStateChanged` events as part of the typical application
lifecycle.

Liveness and Readiness Probes (`HealthIndicator` components and health
groups) are still configured only when deployed on Kubernetes.

This commit also improves the documentation around Probes best practices
and container lifecycle considerations.

See gh-19593
This commit is contained in:
Brian Clozel
2020-03-20 23:49:28 +01:00
parent 3edc1c3a7d
commit ffdf9a422f
30 changed files with 521 additions and 354 deletions
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21
spring-boot-project/spring-boot-docs/src/docs/asciidoc/deployment.adoc
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@@ -184,8 +184,27 @@ TIP: The https://github.com/pivotal-cf/java-cfenv/[Java CFEnv] project is a bett
[[cloud-deployment-kubernetes]]
=== Kubernetes
Spring Boot auto-detects Kubernetes deployment environments by checking the environment for `"*_SERVICE_HOST"` and `"*_SERVICE_PORT"` variables.
You can override this detection with the configprop:spring.main.cloud-platform[] configuration property.
Spring Boot helps you to <<spring-boot-features.adoc#boot-features-kubernetes-application-state,manage the state of your application>> and export it with <<production-ready-features.adoc#production-ready-kubernetes-probes, HTTP Kubernetes Probes using Actuator>>.
Spring Boot helps you to <<spring-boot-features.adoc#boot-features-application-availability-state,manage the state of your application>> and export it with <<production-ready-features.adoc#production-ready-kubernetes-probes, HTTP Kubernetes Probes using Actuator>>.
[[cloud-deployment-kubernetes-container-lifecycle]]
==== Kubernetes Container Lifecycle
When Kubernetes deletes an application instance, the shutdown process involves several subsystems concurrently: shutdown hooks, unregistering the service, removing the instance from the load-balancer...
Because this shutdown processing happens in parallel (and due to the nature of distributed systems), there is a window during which traffic can be routed to a pod that has also begun its shutdown processing.
You can configure a sleep execution in a pre-stop hook to avoid requests being routed to a pod that has already begun shutting down.
This sleep should be long enough for new requests to stop being routed to the pod and its duration will vary from deployment to deployment.
[source,yml,indent=0]
----
lifecycle:
preStop:
exec:
command: ["sh", "-c", "sleep 10"]
----
Once the pre-stop hook has completed, SIGTERM will be sent to the container and <<spring-boot-features#boot-features-graceful-shutdown,graceful shutdown>> will begin, allowing any remaining in-flight requests to complete.
[[cloud-deployment-heroku]]