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Carlos Mendible
Carlos Mendible

Posted on • Originally published at carlos.mendible.com on

Kubernetes: Mount a file in your Pod using a ConfigMap

#kubernetes #configmap #volume #pod

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"
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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"
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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
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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.

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