Kubernetes: Mount a file in your Pod using a ConfigMap

Kubernetes: Mount a file in your Pod using a ConfigMap

Lately I’ve been learning Go and this week I started a side project named kube-sherlock. The purpose of this small program is to list any pod that does not have the labels that your organization requires.

For kube-sherlock I created a dockerfile were both the program (kube-sherlock) and the default configuration (config.yaml) are placed in the app folder:

FROM golang:1.11.5 AS build
WORKDIR /src
ADD go.mod go.sum ./
RUN go get -v
ADD kube-sherlock.go config.yaml ./
RUN CGO_ENABLED=0 GOOS=linux go build -a -ldflags '-w'

FROM alpine:3.7
COPY --from=build src/config.yaml app/config.yaml
COPY --from=build src/kube-sherlock app/kube-sherlock
WORKDIR /app
CMD ./kube-sherlock

# Metadata
ARG BUILD_DATE
ARG VCS_REF
LABEL org.label-schema.build-date=$BUILD_DATE \
    org.label-schema.name="kube-sherlock" \
    org.label-schema.description="Check if labels are applied to your containers" \
    org.label-schema.url="https://github.com/cmendible/kube-sherlock" \
    org.label-schema.vcs-ref=$VCS_REF \
    org.label-schema.vcs-url="https://github.com/cmendible/kube-sherlock" \
    org.label-schema.schema-version="0.1"

So what if you want to replace the default configuration?

You can achieve this with the help of a ConfigMap, creating a new config.yaml with your custom values:

apiVersion: v1
kind: ConfigMap
metadata:
  name: sherlock-config
  namespace: default
data:
  config.yaml: |
    namespaces:
      - default
    labels:
      - "app"
      - "owner"    

Note: I’m using the name of the file as the key.

And then create a pod definition, referencing the ConfigMap:

apiVersion: v1
kind: Pod
metadata:
  name: kube-sherlock
spec:
  serviceAccountName: kube-sherlock
  containers:
    - name: kube-sherlock
      image: cmendibl3/kube-sherlock:0.1
      volumeMounts:
      - name: config-volume
        mountPath: /app/config.yaml
        subPath: config.yaml
  volumes:
    - name: config-volume
      configMap:
        name: sherlock-config
  restartPolicy: Never

Note: the volume references the ConfigMap (sherlock-config), the volume mount specifies the mountPath as the file you want to replace (/app/config.yaml) and the subPath property is used to reference the file by key (config.yaml)

Hope it helps.

Learn More

Storage options for applications in Azure Kubernetes Service (AKS)

Last modified December 9, 2024: docsy (29f80e9)