Day 62 · Kubernetes

Kubernetes Secrets

By Published Kubernetes~1h to complete

Technical Overview

Applications frequently require sensitive data to run—such as database credentials, API keys, SSH private keys, TLS certificates, and software license keys. Hardcoding these credentials inside container images or Pod environment fields compromises security and violates Twelve-Factor App guidelines.

To address this, Kubernetes provides Secrets. Secrets allow you to store and manage sensitive information independently of container images, namespaces, or Pod specs.

graph TD File["Secret File (/opt/beta.txt)"] -->|kubectl create secret| SecretAPI["Secret API Object: beta <br> (base64 encoded in etcd)"] SecretAPI -->|Mounted as volume| Pod["Pod: secret-datacenter"] Pod -->|Maps file decrypting value| ContainerPath["/opt/cluster/beta.txt <br> (tmpfs memory storage)"]

Kubernetes Secrets Deep Dive

A Kubernetes Secret object stores credentials in key-value format inside etcd (the cluster database).

Secret Types

Kubernetes supports several types of Secrets depending on the target use case:

  • Opaque (Default): Generic user-defined arbitrary key-value pairs (used for passwords, license files, custom configuration keys).
  • kubernetes.io/service-account-token: Used by ServiceAccounts to store token credentials for communicating with the Kubernetes API server.
  • kubernetes.io/dockerconfigjson: Used to store credentials for accessing private container registries (imagePullSecrets).
  • kubernetes.io/tls: Used to store a public/private key pair (tls.crt and tls.key) for SSL/TLS endpoints (e.g., Ingress Controllers).

Methods of Creating Secrets

1. From a File

When creating a secret from a file, the filename becomes the key inside the secret mapping, and the contents of the file become the value.

kubectl create secret generic beta --from-file=/opt/beta.txt

2. From Literal Key-Values

Allows creating key-value pairings directly from shell arguments:

kubectl create secret generic database-secret --from-literal=db-password=mySuperSecr3t

Mounting Secrets inside Pods

Pods can consume Secrets in two primary ways:

A. Injected as Environment Variables

Ideal for applications that expect config credentials through process environment setups.

env:
- name: APP_LICENSE_NUMBER
  valueFrom:
    secretKeyRef:
      name: beta
      key: beta.txt

B. Mounted as Files in a Volume

In this method, the secret values are mounted under a specific directory. Kubernetes creates a file for each key in the secret map, and the content of that file is the decrypted secret value.

  • Security Benefit: Volume-mounted secrets are backed by a tmpfs (temporary memory-backed filesystem). This ensures that the secret keys never touch the physical disks of the worker nodes.
volumeMounts:
- name: secret-volume
  mountPath: /opt/cluster
volumes:
- name: secret-volume
  secret:
    secretName: beta

Critical Security Practices for Secrets

CAUTION

  • Base64 is NOT Encryption: By default, Kubernetes Secret values are stored as Base64 encoded strings in etcd, which is just a text representation and offers no security. Anyone with API access or etcd backup access can decode the secrets instantly: echo <secret> | base64 --decode.
  • Encryption at Rest: Ensure that the Kubernetes Control Plane has encryption at rest configured. This encrypts secret data before writing it to etcd.
  • Role-Based Access Control (RBAC): Restrict access to Secret resources (get, list, watch) to only authorized users and service accounts to prevent security leaks.

Infrastructure & Configuration Requirements

  • Target Cluster: Nautilus Kubernetes Cluster
  • Jump Host User: thor
  • Namespace: default
  • Source Secret File: /opt/beta.txt on the node
  • Output Secret Details:
    • Name: beta
    • Type: Opaque
  • Pod Details:
    • Name: secret-datacenter
    • Container Name: secret-container-datacenter
    • Image: fedora:latest
    • Mount Path: /opt/cluster
    • Command: ["/bin/sh", "-c", "sleep 3600"] (keeps container running)

Step-by-Step Implementation

Step 1: Connect to the Kubernetes Jump Host

SSH into the command host:

ssh thor@jump_host_ip

Step 2: Create the Generic Secret

Verify the content of the license key file inside the /opt directory:

cat /opt/beta.txt

Create the Opaque secret named beta using the file as source:

kubectl create secret generic beta --from-file=/opt/beta.txt

Expected Output:

secret/beta created

Step 3: Define the Pod Manifest File

Create a YAML configuration file named secret-pod.yaml. This file configures the Pod to reference the beta secret and mount it to /opt/cluster:

apiVersion: v1
kind: Pod
metadata:
  name: secret-datacenter
  labels:
    app: secret-app
spec:
  volumes:
  - name: secret-volume-cluster
    secret:
      secretName: beta
  containers:
  - name: secret-container-datacenter
    image: fedora:latest
    command: ["/bin/sh", "-c", "sleep 3600"]
    volumeMounts:
    - name: secret-volume-cluster
      mountPath: /opt/cluster
      readOnly: true

Step 4: Deploy the Pod

Apply the manifest file to start container creation inside the namespace:

kubectl apply -f secret-pod.yaml

Expected Output:

pod/secret-datacenter created

Ensure the Pod is in a healthy, running status:

kubectl get pods

Expected Output:

NAME                READY   STATUS    RESTARTS   AGE
secret-datacenter   1/1     Running   0          10s

Post-Deployment Verification

1. Retrieve and Decode Secret Metadata

Check the secret's Base64 representation in the cluster:

kubectl get secret beta -o yaml

Expected Output showing base64 value:

apiVersion: v1
data:
  beta.txt: dGVzdFBhc3N3b3JkMTIzCg==
kind: Secret
...

Decode the value to confirm it matches the raw password:

echo "dGVzdFBhc3N3b3JkMTIzCg==" | base64 --decode

Expected Output:

testPassword123

2. Verify Decrypted Secrets inside the Pod Container

Log into the running container and verify the secret file was automatically decrypted and mapped under /opt/cluster:

kubectl exec -it secret-datacenter -c secret-container-datacenter -- cat /opt/cluster/beta.txt

Expected Output:

testPassword123

The secret has been successfully mounted and decrypted inside the container!

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