K
Q

Define Environment Variables referring to variable environment for a Container [kubernetes]

4/9/2020

I have a K8s deployment for a spring boot application I want to create a dump file .hprof with the name of the pod ($hostname)

My JAVA_OPTIONS parameters is a variable environment I want to refer to another variable inside the parent JAVA_Options

containers:
- env:
  - name: SPRING_PROFILES_ACTIVE
    value: prod,swagger
  - name: JAVA_OPTS
    value: ' -XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/$HOSTNAME.hprof'

What I expected is to have a variable that contains the hostname :

$ echo $JAVA_OPTS -XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/myPodNameStaging.hprof

What I have as a result is: $HOSTNAME.hprof is set as a string.

I also tried many combinations $(HOSTNAME) ${HOSTNAME}. Always I got the name of the variable and not the content value.

My question is: How to refer to the $HOSTNAME

-- Hamdy
containers
kubernetes
kubernetes-pod
linux
maven

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3 Answers

4/10/2020

I'm trying this using nginx, however the variable substitution is working, perhaps you can try it:

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2 # tells deployment to run 2 pods matching the template
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80
        env:
        - name: POD_HOSTNAME
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        - name: SPRING_PROFILES_ACTIVE
          value: prod,swagger
        - name: JAVA_OPTS
          value: -XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/$(POD_HOSTNAME).hprof

And after that I can see the content of JAVA_OPTS:

root@nginx-deployment-5bc5fcdc8b-f4ldx:/# echo $JAVA_OPTS
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/10.32.17.138.hprof
-- irvifa
Source: StackOverflow
4/9/2020

This is not possible. You will need to define these some other way or otherwise handle the interpolation yourself. A common option is something like this:

command:
- sh
- -c
- |
  JAVA_OPTS="asdfasdf" java -whatever

But that does require fully overriding the command from the underlying container which is annoying. That said, you can do limited replacements in volume paths so probably handle it at that level instead for this particular case.

-- coderanger
Source: StackOverflow
4/10/2020

The hostname of pods in Kubernetes is always the same as the pod name and on Linux we have a env variable $HOSTNAME. So you can use it to achieve what you need:

Here is an example that may suit your needs:

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  namespace: default
spec:
  containers:
  - name: busybox
    image: k8s.gcr.io/busybox:1.24 
    env:
    - name: SPRING_PROFILES_ACTIVE
      value: prod,swagger    
    command: [ "sh", "-c"]
    args:
    - while true; do
        export JAVA_OPTS="-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/$HOSTNAME.hprof";
        printenv JAVA_OPTS;
        printenv SPRING_PROFILES_ACTIVE;
        sleep 10;
      done;
    imagePullPolicy: IfNotPresent
  restartPolicy: Always

If you run kubectl get logs busybox you can see this output:

-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-XX:MaxRAMPercentage=50 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/jvm-data/busybox.hprof
prod,swagger
-- mWatney
Source: StackOverflow