OpenShift-Examples/Custom-HTTP-Probe/README.md

Custom HTTP Probe

Context

An application is deployed in OpenShift and has no built-in liveness/readiness probes. This example shows how to implement a custom probe.

The sample application

This sample app has three probes:

• a standard liveness probe
• a standard readiness probe
• a custom probe

The app takes about 30 seconds to boot and then exhibit two endpoints:

• /please-die will switch the liveness probe to "dead"
• /please-resuscitate will switch the liveness probe to "alive"

The custom probe is a mix of everything you can find in a business app:

• when the app is alive, it returns a non-200 HTTP status with JSON content
• when the app is dead, it returns a 500 HTTP status with HTML content

Deploy the sample application

oc new-app nodejs~https://github.com/nmasse-itix/OpenShift-Examples.git --name myapp --context-dir=Custom-HTTP-Probe
oc expose svc/myapp

Play with it

export SAMPLE_APP_URL="http://$(oc get route myapp -o jsonpath='{.spec.host}')" && echo $SAMPLE_APP_URL

Print some help:

curl $SAMPLE_APP_URL/ -D -

Check if the app is ready:

curl $SAMPLE_APP_URL/probe/readiness -D -

Let the app die:

curl $SAMPLE_APP_URL/please-die -D -

Check if the app is alive:

curl $SAMPLE_APP_URL/probe/liveness -D -

Let the app resuscitate:

curl $SAMPLE_APP_URL/please-resuscitate -D -

Inspect the custom probe:

curl $SAMPLE_APP_URL/please-die -D -
curl $SAMPLE_APP_URL/probe/custom -D -

curl $SAMPLE_APP_URL/please-resuscitate -D -
curl $SAMPLE_APP_URL/probe/custom -D -

Use the standard probes

Add the liveness probe:

oc patch dc myapp --type=json -p '[ { "op": "add", "path": "/spec/template/spec/containers/0/livenessProbe", "value": { "initialDelaySeconds": 5, "timeoutSeconds": 5, "httpGet": { "path": "/probe/liveness", "port": 8080 } } } ]'

Add the readiness probe:

oc patch dc myapp --type=json -p '[ { "op": "add", "path": "/spec/template/spec/containers/0/readinessProbe", "value": { "initialDelaySeconds": 20, "timeoutSeconds": 5, "httpGet": { "path": "/probe/readiness", "port": 8080 } } } ]'

Watch the deployment:

oc get pods -w

Let the app die:

curl $SAMPLE_APP_URL/please-die -D -

Watch the app being restarted:

oc get pods -w

Use the custom probe

Review the probe.py code.

Create a configMap containing the custom probe code:

oc create configmap myapp-probe --from-file probe.py

Mount the configMap on /opt/probe:

oc volume dc/myapp --add --overwrite --type=configMap --configmap-name=myapp-probe --default-mode=755 --mount-path=/opt/probe --name probe --confirm

Replace the standard liveness and readiness probes by the custom one:

oc patch dc myapp --type=json -p '[ { "op": "replace", "path": "/spec/template/spec/containers/0/livenessProbe", "value": { "initialDelaySeconds": 5, "timeoutSeconds": 5, "exec": { "command": [ "/opt/probe/probe.py", "http://localhost:8080/probe/custom" ] } } } ]'

oc patch dc myapp --type=json -p '[ { "op": "replace", "path": "/spec/template/spec/containers/0/readinessProbe", "value": { "initialDelaySeconds": 5, "timeoutSeconds": 5, "exec": { "command": [ "/opt/probe/probe.py", "http://localhost:8080/probe/custom" ] } } } ]'

Let the app die:

curl $SAMPLE_APP_URL/please-die -D -

Watch the app being restarted:

oc get pods -w