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Question

IndentationError: unexpected indent, thrown by Python 3. Code used in Kubernetes args entry in Pod deployment YAML

4/1/2019

goal and the issue

To have a container/Pod deployment that can be continously running. The command the container should execute is: /usr/local/bin/python3 and the args to the command are: "-c

#x27;import time\\nwhile (True):\\n print(\".\");time.sleep(5);'". However, when I execute kubectl apply -f "PATH_TO_THE_KUBERNETES_YAML_FILE" the deployment errs with this Python exception: IndentationError: unexpected indent.

A screenshot of the error:

The Pod deployment is used as the medium for calling Python code that interacts with the Certbot client as part of tasks when using LetsEncrypt certificates.

See the project here

So it should be possible to deploy the Pod >> do a kubectl exec ... into the container running as part of the Kubernetes deployment.

tried:

Various ways of defining the Kubernetes command args line.

Via the exec Python option. E.g.: python3 -c exec(\"import time\nwhile True: print(\".\");time.sleep(5);\")
Enclosing the code to execute with different combinations of ` and ".
#x27;textwrap.dedent("""import time while True: print(".") time.sleep(5)""")'...
tried using:
```
args:
 - "-c 
#x27;import time\\nwhile (True):\\n print(\".\");time.sleep(5);'"
```
as an alternative to args: ["-c
#x27;import time\\nwhile (True):\\n print(\".\");time.sleep(5);'"]
confirmed that the Python code itself works.
both by using Python3 -c "..." directly and by calling it via a docker run command to a container from this Dockerfile
I have done the usual Googling, Stack* search and so forth. I've also been on the official Kubernetes GitHub repo page and search through the issues there. Closed as well as open. And I have not seen any issue matching this one.
Kubectl does not complain when doing ...apply -f YAML_FILE, in regards to the format of the YAML file and to the adherence of the Pod deployment specification.
Tried with some bash code instead: ["/bin/bash", "-ecx", "while :; do printf '.'; sleep 5 ; done"]<-- that works.

further info

Python is v3.7.2
Kubernetes is v1.12.5-gke.10

It seems to be the combination of specifying the Python code in a Kubernetes Pod deployment YAML file ... that doesn't go well with Pythons requirement of significant whitespace and indentation. As you can read in the #tried section, it works when calling Python directly or via a Docker run/exec command.

How can I troubleshoot this?

-- Lars Bingchong

containers

google-kubernetes-engine

kubernetes

python

yaml

1 Answer

4/9/2019

So I was able to get help on this on the Kubernetes Slack channel. It was a YAML syntax issue.

The following in the Pod deployment YAML file solved it

  args:
    - |-
      -c
      import time
      while True:
          print('.')
          time.sleep(5)

this works in combination with the Dockerfile's....

FROM larssb/certbot-dns-cloudflare-python3
LABEL author="https://github.com/larssb"

#
# Container config
#
WORKDIR /letsencryptit

#
# COPY IN DATA
#
COPY ./scripts /scripts/
COPY ./letsencryptit /letsencryptit/

#
# INSTALL
#
RUN pip install --upgrade google-api-python-client --disable-pip-version-check --no-cache-dir \
    && pip install --upgrade oauth2client --disable-pip-version-check --no-cache-dir \
    && pip install --upgrade sty --disable-pip-version-check --no-cache-dir \
    && chmod +x /scripts/deploy-hook-runner.sh

# Set an ENTRYPOINT to override the entrypoint specified in certbot/certbot
ENTRYPOINT ["/usr/local/bin/python3"]
CMD ["-c"]

ENTRYPOINT, as this is re-used by the Pod deployment. However, the Dockerfile's CMD is overwritten by the args property in the Pod deployment YAML file.

The args property explained in detail

The -c is a parameter to the Python binary
The rest is std. Python code, to have the container, deployed via the Pod deployment, continuously run so that it can be on standby for command calls to it via kubectl exec

The key

This part of the args property > - |-. It strips the line feed and any trailing blank lines. Making it possible to state a multi-line Python block of code

Documentation

A gist with example code on the required syntax in the args property. Find it here.
The Dockerfile used
The Kubernetes Pod deployment YAML file. Check it out here
On the YAML "strip" syntax

Kudos to @wizzwizz4, @a_guest for your comments and suggestions. They helped me troubleshoot this, narrow in on a solution. Also a big thank you to Mr. @grampelberg on the Kubernetes Slack channel for assisting me and providing the solution.