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I'm running into an issue where it seems I can only run a python command in either the dockerfile or Kubernetes. Right now I have two python scripts, the first script setting up keys and tokens so the second script can run properly.

My dockerfile looks something like this:

FROM python:3.8.0-alpine
WORKDIR /code
COPY script1.py .
COPY script2.py .

# Install python libraries
RUN pip install --upgrade pip
RUN apk add build-base
RUN apk add linux-headers
RUN pip install -r requirements.txt

CMD [ "python", "-u", "script2.py"]

and my Kubernetes yaml file is:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: script2
  labels:
    app: script2-app
spec:
  selector:
    matchLabels:
      app: script2-app
  replicas: 1
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  template:
    metadata:
      labels:
        app: script2-app
    spec:
      containers:
      - name: script2-app
        image: script2:v1.0.1
        ports:
          - containerPort: 5000
        env:
          - name: KEYS_AND_TOKENS
            valueFrom:
              secretKeyRef:
                name: my_secret
                key: KEYS_AND_TOKENS
        command:
          - "python"
          - "script1.py"

The issue starts with the 'command' portion in the yaml file. Without it, Kubernetes will run the container as usual. (the container can still run without the keys and tokens. It will just log that some functions failed to run then move on.) However, when I include the 'command' portion, script1 will run and successfully set up the keys. But once script1 finishes, nothing else happens. The deployment continues to run but script2 never starts.

The reason I am doing it this way is because script2 may need to restart on occasion due to internet connection failures causing it to crash. Sence all script1 is doing is setting up keys and tokens, it only needs to run once, then things will be set up for as long as the pod lives. I don't want to verify the keys and tokens every time script2 restarts. This is why the two scripts are separate and why I'm only running script1 in startup.

Any help would be much appreciated!

boblerbob
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1 Answers1

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What is happening?

The command supplied through the yaml file overrides the CMD in the dockerfile (you can refer the kubernetes documentation here). So, when you supply command for executing the script1 in the yaml file, it overrides the command (CMD) in dockerfile for the execution of script2 because of which you must be getting errors as per your code logic.

How to resolve?

Step 1: Create a bash file as follows: (naming it "run.sh")

#!/bin/bash

exec python3 /path/to/script1.py
exec python3 /path/to/script2.py

Step 2: Update the dockerfile as:

FROM python:3.8.0-alpine
WORKDIR /code
COPY script1.py .
COPY script2.py .
COPY run.sh . # copying the bash file

# Install python libraries
RUN pip install --upgrade pip
RUN apk add build-base
RUN apk add linux-headers
RUN pip install -r requirements.txt

RUN chmod a+x run.sh # making it executable
CMD ["./run.sh"] # executing the scripts through bash file

Step 3: Remove the command from the kubernetes deployment yaml

But if you want to keep the command in the yaml file then you should replace it with "./run.sh"

Note: Ideally you should not run two different scripts like this. If you need to set up tokens/keys you should do that in a sub-module which you can call in your main script. You can handle network connectivity issues, etc. through a combination of exception handling and a retry mechanism.

Chayan Bansal
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