Liveness, Readiness and Startup Probes
In Kubernetes, a probe is a mechanism used to determine the health of an application running in a container. Kubernetes uses probes to know when a container will be restarted, ready, and started.
There are three types of probes available in Kubernetes:
Liveness Probe: It checks whether the application running inside the container is still alive and functioning properly. If the liveness probe fails, Kubernetes considers the container to be in a failed state and restarts it. This is useful when an application gets into an unrecoverable state or becomes unresponsive.
Readiness Probe: It determines whether the application inside the container is ready to accept traffic or requests. When a readiness probe fails, Kubernetes stops sending traffic to the container until it passes the probe. This is useful during application startup or when the application needs some time to initialize before serving traffic.
Startup Probe (introduced in Kubernetes 1.16): It is similar to a readiness probe, but it only runs during the initial startup of a container. The purpose of the startup probe is to differentiate between a container that's starting up and one that's in a crashed state. Once the startup probe succeeds, it is disabled, and the readiness probe takes over.
In this example, we assume you have a Spring Boot application deployed as a container with an image specified by your-image:latest. The container listens on port 8080.
The liveness/readiness probe is defined using an HTTP GET request to the /actuator/health endpoint, which is provided by Spring Boot Actuator. This endpoint exposes application health information.
apiVersion: apps/v1
kind: Deployment
metadata:
name: spring-app
spec:
replicas: 1
selector:
matchLabels:
app: spring-app
template:
metadata:
labels:
app: spring-app
spec:
containers:
- name: spring-container
image: your-image:latest
ports:
- containerPort: 8080
livenessProbe:
httpGet:
path: /actuator/health
port: 8080
initialDelaySeconds: 60
periodSeconds: 10
failureThreshold: 3
readinessProbe:
httpGet:
path: /actuator/health
port: 8080
initialDelaySeconds: 60
periodSeconds: 10
failureThreshold: 3
initialDelaySeconds 60 seconds specifies the delay before the probe starts executing after the container starts.
periodSeconds 10 seconds means that the probe will be executed every 10 seconds.
failureThreshold 3 indicates that the container will be marked as unhealthy after three consecutive failed probes.
More detail:
Sr. Software Developer — Java / Spring / k8s / Kafka | https://github.com/omernaci
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