Openshift - Run a basic container with alpine, java and jmeter

Question

In an Openshift environment (Kubernetes v1.18.3+47c0e71) I am trying to run a very basic container which will contain:

Alpine (latest version)
JDK 1.8
Jmeter 5.3

I just want it to boot and run in a container, expecting connections to run Jmeter CLI from the command line terminal.

I have gotten this to work perfectly in my local Docker distribution. This is the Dokerfile content:

FROM alpine:latest

ARG JMETER_VERSION="5.3"
ENV JMETER_HOME /opt/apache-jmeter-${JMETER_VERSION}
ENV JMETER_BIN  ${JMETER_HOME}/bin
ENV JMETER_DOWNLOAD_URL https://archive.apache.org/dist/jmeter/binaries/apache-jmeter-${JMETER_VERSION}.tgz

USER root

ARG TZ="Europe/Amsterdam"
RUN    apk update \
    && apk upgrade \
    && apk add ca-certificates \
    && update-ca-certificates \
    && apk add --update openjdk8-jre tzdata curl unzip bash \
    && apk add --no-cache nss \
    && rm -rf /var/cache/apk/ \
    && mkdir -p /tmp/dependencies  \
    && curl -L --silent ${JMETER_DOWNLOAD_URL} >  /tmp/dependencies/apache-jmeter-${JMETER_VERSION}.tgz  \
    && mkdir -p /opt  \
    && tar -xzf /tmp/dependencies/apache-jmeter-${JMETER_VERSION}.tgz -C /opt  \
    && rm -rf /tmp/dependencies

# Set global PATH such that "jmeter" command is found
ENV PATH $PATH:$JMETER_BIN

WORKDIR ${JMETER_HOME}

For some reason, when I configure a Pod with a container with that exact configuration previously uploaded to a private Docker images registry, it does not work.

This is the Deployment configuration (yaml) file (very basic aswell):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: jmeter
  namespace: myNamespace
  labels:
    app: jmeter
    group: myGroup
spec:
  selector:
    matchLabels:
      app: jmeter
  replicas: 1
  template:
    metadata:
      labels:
        app: jmeter
    spec:
      containers:
        - name: jmeter
          image: myprivateregistry.azurecr.io/jmeter:dev
          resources:
            limits:
              cpu: 100m
              memory: 500Mi
            requests:
              cpu: 100m
              memory: 500Mi
          imagePullPolicy: Always
      restartPolicy: Always
      imagePullSecrets:
        - name: myregistrysecret

Unfortunately, I am not getting any logs:

A screenshot of the Pod events:

Unfortunately, not getting either to access the terminal of the container:

Any idea on:

how to get further logs?
what is going on?

Your Dockerfile doesn't have a `CMD`. How does the pod know what command to run? (If it's just going to run a one-off load test, a Job might be a better match than a Deployment.) — David Maze, Oct 21 '20 at 17:48
Thanks for your comment. As I said in my question, this configuration works perfectly in local. Maybe the question is: in terms of using or not that CMD instruction, what is the difference between a local Docker environment and Kubernetes? What instruction should I give to that CMD command if I just want the operating system Alpine to be set up when the pod starts? — ElPiter, Oct 21 '20 at 18:29

score 2 · Accepted Answer · answered Oct 21 '20 at 20:05

On your local machine, you are likely using docker run -it <my_container_image> or similar. Using the -it option will run an interactive shell in your container without you specifying a CMD and will keep that shell running as the primary process started in your container. So by using this command, you are basically already specifying a command.

Kubernetes expects that the container image contains a process that is run on start (CMD) and that will run as long as the container is alive (for example a webserver).

In your case, Kubernetes is starting the container, but you are not specifying what should happen when the container image is started. This leads to the container immediately terminating, which is what you can see in the Events above. Because you are using a Deployment, the failing Pod is then restarted again and again.

A possible workaround to this is to run the sleep command in your container on startup by specifing a command in your Pod like so:

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:
  - name: command-demo-container
    image: alpine
    command: ["/bin/sleep", "infinite"]
  restartPolicy: OnFailure

(Kubernetes documentation)

This will start the Pod and immediately run the /bin/sleep infinite command, leading to the primary process being this sleep process that will never terminate. Your container will now run indefinitely. Now you can use oc rsh <name_of_the_pod to connect to the container and run anything you would like interactively (for example jmeter).

Your answer is just perfect. I was thinking of a solution similar to yours... using a constant ping or something like that. A sleep infinity is a good idea Thank you very much. — ElPiter, Oct 21 '20 at 20:34

Openshift - Run a basic container with alpine, java and jmeter

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