Kubernetes pod yaml: source command does not work

Question

In the following pod yaml, I cannot get source command to work. Initially I inserted the command under args between echo starting and echo done and now I tried {.lifecycle.postStart} to no avail.

apiVersion: v1
kind: Pod
metadata:
  name: mubu62
  labels:
    app: mubu62
spec:
  containers:
  - name: mubu621
    image: dockreg:5000/mubu6:v6
    imagePullPolicy: Always
    ports:
    - containerPort: 5021
    command: ["/bin/sh","-c"]
    args: 
    - echo starting;
      echo CONT1=\"mubu621\" >> /etc/environment;
      touch /mubu621;
      sed -i 's/#Port 22/Port 5021/g' /etc/ssh/sshd_config;
      sleep 3650d;
      echo done;
    lifecycle:
      postStart:
        exec:
          command: ["/bin/bash","-c","source /etc/environment"]
  - name: mubu622
    image: dockreg:5000/mubu6:v6
    imagePullPolicy: Always
    ports:
    - containerPort: 5022
  imagePullSecrets:
  - name: regcred
  nodeName: spring
  restartPolicy: Always

Kubectl apply throws no errors, but echo $CONT1 returns nada! mubu6 is an ubuntu modified image.

The reason I am doing this, is because when I ssh from another pod in this pod (mubu621), Kubernetes environment variables set through env are not seen in the ssh session.

Any help would be much appreciated!

`"/bin/bash","-c","source /etc/environment"` starts a session, source /etc/environment, then dissapear right away. That's why you cannot access variables sourced. — Philippe, Dec 18 '21 at 17:02
Should I also add a `sleep` command after that then? Under `args` where I do have a `sleep` command in the end, it also did not work. — Alexander Sofianos, Dec 18 '21 at 17:29
I now used `["/bin/bash","-c","source /etc/environment","sleep 3650d"]`, but I still cannot `echo $CONT1`. — Alexander Sofianos, Dec 18 '21 at 17:37

Alexander Sofianos · Accepted Answer · 2021-12-25T17:52:34.470

After experimenting with the suggestions under set-environment-variable-automatically-upon-ssh-login, what worked was to substitute

echo CONT1=\"mubu621\" >> /etc/environment;

with

echo CONT1=\"mubu621\" >> /root/.bashrc;

and delete

lifecycle:
      postStart:
        exec:
          command: ["/bin/bash","-c","source /etc/environment"]

that didn't work anyway.

Upon SSH-ing from container mubu622 to container mubu621, I can now successfully execute echo $CONT1 with mubu621 output, without having to source /root/.bashrc first, which was initially the case with writing the env_variable in /etc/environment.

In summary: when using a bash shell in kubernetes containers, you can SSH from another container and echo variables written in /root/.bashrc without sourcing (because kubernetes env_variables are not available in a ssh session). This is very useful e.g in the case of multi-container pods, so you know amongst other things in which container you are currently logged in.

score 1 · Answer 2 · answered Dec 18 '21 at 23:48

TLDR

Move the env variable into env section of your pod spec:

apiVersion: v1
kind: Pod
metadata:
  name: mubu62
  labels:
    app: mubu62
spec:
  containers:
  - name: mubu621
    image: dockreg:5000/mubu6:v6
    imagePullPolicy: Always
    ports:
    - containerPort: 5021
    command: ["/bin/sh","-c"]
    env:
    - name: CONT1
      value: mubu621

Explanation

As one of the comments already indicated - your source command probably works, but only in the context where it's executed. If you'd like this to be applied for other commands - use the env field of the container spec. Consider this minimalistic example, using busybox:

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  labels:
    app: busybox
spec:
  containers:
  - name: busybox
    image: busybox
    command: ["/bin/sh", "-ec", "sleep 1000"]
    env:
    - name: TEST_ENV
      value: "test_val"

with this - when you run the env command inside the pod - you'll see the TEST_ENV appear as expected:

$ kubectl exec -it busybox-6d467f94db-sj9nz env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=busybox-6d467f94db-sj9nz
TERM=xterm
TEST_ENV=test_val
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
KUBERNETES_SERVICE_HOST=10.96.0.1
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT=tcp://10.96.0.1:443
HOME=/root

Read more about env variables in pods in Kubernetes docs

Thanks a lot andrzejwp, but as I mention in my question, I have already tried your suggestion, but does not work when I `ssh` from another pod. I want a variable I can `echo` in a `ssh session`. — Alexander Sofianos, Dec 19 '21 at 06:48
Sorry, didn't get that part initially. But if you're SSH-ing into the pod and want that env set for each connection - I think you should look at the SSH configuration, or even the shell itself. See https://unix.stackexchange.com/questions/101168/set-environment-variable-automatically-upon-ssh-login-no-root-access — andrzejwp, Dec 20 '21 at 10:23

Kubernetes pod yaml: source command does not work

2 Answers2

TLDR

Explanation