One of the most common questions that I get asked as a consultant is: "What is the difference between liveness and readiness samples?" The next most common question is: "Which ones do my application need?"
Anyone who has tried this question behind Duck Duck Go knows that it is not easy to find an answer to it on the internet. In this article, I hope I can help you answer these questions yourself. I will share my opinion on how best to use liveness and readiness of probes in applications deployed in Red Hat OpenShift . And I'm not suggesting a rigorous algorithm, but rather a general framework that you can use to make your own architectural decisions.
To make the abstractions more specific, I suggest looking at four general application examples. For each of them, we will find out whether we need to configure the liveness and readiness probes, and if necessary, how. Before moving on to examples, let's take a closer look at these two different types of samples.
: Kubernetes “startup” probe, OpenShift 4.5 clusters. startup probe, liveness readiness probes. startup probes.
Liveness readiness probes
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apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: application-nginx
name: application-nginx
spec:
replicas: 1
selector:
matchLabels:
app: application-nginx
template:
metadata:
labels:
app: application-nginx
spec:
# Will appear below as it changes
:
spec:
containers:
- image: quay.io/<username>/nginx:latest
name: application-nginx
imagePullPolicy: Always
ports:
- containerPort: 8443
protocol: TCP
readinessProbe:
httpGet:
scheme: HTTPS
path: /index.html
port: 8443
initialDelaySeconds: 10
periodSeconds: 5
2: ( REST API)
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spec:
containers:
- image: quay.io/<username>/my-application-jobs:latest
name: my-application-jobs
imagePullPolicy: Always
livenessProbe:
exec:
command:
- /bin/sh
- -c
- "/usr/bin/my-application-jobs --alive"
initialDelaySeconds: 10
periodSeconds: 5
readiness ?
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initialDelaySeconds: 10
periodSeconds: 5
readiness ?
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readinessProbe:
httpGet:
scheme: HTTPS
path: /healthz
port: 8443
initialDelaySeconds: 10
periodSeconds: 5
, YAML :
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: backend-service
name: backend-service
spec:
replicas: 1
selector:
matchLabels:
app: backend-service
template:
metadata:
labels:
app: backend-service
spec:
containers:
- image: quay.io/<username>/backend-service:latest
name: backend-service
imagePullPolicy: Always
ports:
- containerPort: 8443
protocol: TCP
readinessProbe:
httpGet:
scheme: HTTPS
path: /healthz
port: 8443
initialDelaySeconds: 10
periodSeconds: 5
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# Pod One - Application Server and Nginx
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: my-application-web
name: my-application-web
spec:
replicas: 1
selector:
matchLabels:
app: my-application-web
template:
metadata:
labels:
app: my-application-web
spec:
containers:
- image: quay.io/<username>/my-application-nginx:latest
name: my-application-nginx
imagePullPolicy: Always
ports:
- containerPort: 8443
protocol: TCP
livenessProbe:
exec:
command:
- /bin/sh
- -c
- "[ -f /run/nginx.pid ] && ps -A | grep nginx"
initialDelaySeconds: 10
periodSeconds: 5
readinessProbe:
httpGet:
scheme: HTTPS
path: /index.html
port: 8443
initialDelaySeconds: 10
periodSeconds: 5
- image: quay.io/<username>/my-application-app-server:latest
name: my-application-app-server
imagePullPolicy: Always
ports:
- containerPort: 8080
protocol: TCP
livenessProbe:
exec:
command:
- /bin/sh
- -c
- "/usr/bin/my-application-web --alive"
initialDelaySeconds: 10
periodSeconds: 5
readinessProbe:
httpGet:
scheme: HTTP
path: /healthz
port: 8080
initialDelaySeconds: 10
periodSeconds: 5
# Pod Two - Jobs Server
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: my-application-jobs
name: my-application-jobs
spec:
replicas: 1
selector:
matchLabels:
app: my-application-jobs
template:
metadata:
labels:
app: my-application-jobs
spec:
containers:
- image: quay.io/<username>/my-application-jobs:latest
name: my-application-jobs
imagePullPolicy: Always
livenessProbe:
exec:
command:
- /bin/sh
- -c
- "/usr/bin/my-application-jobs --alive"
initialDelaySeconds: 10
periodSeconds: 5
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