<p>I want to set an environment variable (I'll just name it <code>ENV_VAR_VALUE</code>) to a container during deployment through Kubernetes.</p>

<p>I have the following in the pod yaml configuration:</p>

<pre><code>...
...
    spec:
      containers:
      - name: appname-service
        image: path/to/registry/image-name
        ports:
        - containerPort: 1234
        env:
        - name: "ENV_VAR_VALUE"
          value: "some.important.value"
...
...
</code></pre>

<p>The container needs to use the <code>ENV_VAR_VALUE</code>'s value.<br>
But in the container's application logs, it's value always comes out empty.<br>
So, I tried checking it's value from inside the container:</p>

<pre><code>$ kubectl exec -it appname-service bash
root@appname-service:/# echo $ENV_VAR_VALUE
some.important.value
root@appname-service:/# 
</code></pre>

<p>So, the value was successfully set.</p>

<p>I imagine it's because the environment variables defined from Kubernetes are set <strong>after</strong> the container is already initialized.</p>

<p>So, I tried overriding the container's CMD from the pod yaml configuration:</p>

<pre><code>...
...
    spec:
      containers:
      - name: appname-service
        image: path/to/registry/image-name
        ports:
        - containerPort: 1234
        env:
        - name: "ENV_VAR_VALUE"
          value: "some.important.value"
        command: ["/bin/bash"]
        args: ["-c", "application-command"]
...
...
</code></pre>

<p>Even still, the value of <code>ENV_VAR_VALUE</code> is still empty during the execution of the command.<br>
Thankfully, the application has a restart function<br>
-- because when I restart the app, <code>ENV_VAR_VALUE</code> get used successfully.<br>
-- I can at least do some other tests in the mean time.</p>

<h3>So, the question is...</h3>

<blockquote>
  <p>How should I configure this in Kubernetes so it isn't a tad too late in setting the environment variables?</p>
</blockquote>

<p>As requested, here is the Dockerfile.<br>
I apologize for the abstraction...</p>

<pre><code>FROM ubuntu:18.04

RUN apt-get update &amp;&amp; apt-get install -y some-dependencies

COPY application-script.sh application-script.sh

RUN ./application-script.sh

# ENV_VAR_VALUE is set in this file which is populated when application-command is executed
COPY app-config.conf /etc/app/app-config.conf

CMD ["/bin/bash", "-c", "application-command"]
</code></pre>

<p>You can try also running two commands in Kubernetes POD spec:</p>

<ol>
<li>(read in env vars): "source /env/required_envs.env" (would come via <a href="https://kubernetes.io/docs/concepts/configuration/secret/#using-secrets-as-files-from-a-pod" rel="nofollow noreferrer">secret</a> mount in volume)</li>
<li>(main command): "application-command"<br></li>
</ol>

<p>Like this:</p>

<hr>

<pre><code>containers:
  - name: appname-service
    image: path/to/registry/image-name
    ports:
        - containerPort: 1234
    command: ["/bin/sh", "-c"]
    args:
      - source /env/db_cred.env;
        application-command;
</code></pre>
