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Non-root containers in Kubernetes

· 2 min read
Matej Jelluš
Matej Jelluš
Tech leader and IT nerd who is constantly trying new things, sharing his experiences and still enjoys writing code in his free time. Currently looking for new challenges and opportunities.

Container should be able to perform only a very limited set of operations and it is highly recommended to use different user from root. To achieve this both docker file and kubernetes config must be changed.

Create non-root container​

Docker containers run by default with root privileges. Changing the configuration limits the processes that can be executed and adds an extra layer of security.

FROM node:16-alpine

RUN addgroup --gid 3000 --system juffgroup \
  && adduser  --uid 2000 --system --ingroup juffgroup juffuser

USER 2000:3000

...

EXPOSE 3001

CMD [ "node", "dist/index.js" ]

Define securityContext for Pod​

When you want to ensure that no root container will run in your Kubernetes cluster, you can use securityContext for this. If you set runAsNonRoot to true, Kubernetes will check either runAsUser setting (also under securityContext) or USER directive defined in the image (must use numeric UID).

And while we are working with these settings, let's set other recommended policies straight away.

Containers are by default allowed to create, download or modify files. This can be misused by potential attacker. To prevent this, set readOnlyFilesystem to true and the filesystem of the container is read-only. If your application needs to write into filesystem, it is recommended to mount secondary filesystem.

Remove all unnecessary capabilities unless the application really needs it with capabilities setting. You can then add a specific capability if needed.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: node-express-kubernetes-example-deployment
  labels:
    # app, tier, environment, ...
spec:
  replicas: 2
  selector:
    # ...
  template:
    # ...
    spec:
      containers:
      - name: node-express-kubernetes-example-application
        image: registry.digitalocean.com/juffalow/node-express-kubernetes-example:latest
        imagePullPolicy: Always
        ports:
          - containerPort: 3001
        securityContext:
          allowPrivilegeEscalation: false
          readOnlyRootFilesystem: true
          runAsNonRoot: true
          capabilities:
            drop:
              - all
        env:
          # variables
        livenessProbe:
          # liveness probe settings
        readinessProbe:
          # readiness probe settings

References​

You can find working example here with basic Node application and k8s configs.

Official pages:

Tools:

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