Secret types (Opaque, docker-registry, TLS) in Kubernetes - Mini Project: Build & Apply

Kubernetes Secret Types: Opaque, docker-registry, TLS

📖 Scenario: You are managing a Kubernetes cluster for a small company. You need to securely store different types of sensitive data such as generic secrets, Docker registry credentials, and TLS certificates. Kubernetes provides different secret types for these use cases.In this project, you will create three Kubernetes secrets of types Opaque, kubernetes.io/dockerconfigjson, and kubernetes.io/tls to understand how to handle each type.

🎯 Goal: Create three Kubernetes secrets using YAML files: one Opaque secret with a username and password, one docker-registry secret with Docker registry credentials, and one TLS secret with certificate and key files. Then, verify the secrets are created correctly.

📋 What You'll Learn

Create an Opaque secret named my-opaque-secret with username and password data.

Create a docker-registry secret named my-docker-secret with Docker registry credentials.

Create a TLS secret named my-tls-secret with certificate and key files.

Use kubectl commands to apply the secrets and verify their creation.

💡 Why This Matters

🌍 Real World

Kubernetes secrets are used to store sensitive information like passwords, tokens, and certificates securely, preventing them from being exposed in plain text in configuration files or container images.

💼 Career

Knowing how to create and manage different Kubernetes secret types is essential for DevOps engineers and cloud administrators to secure applications running in Kubernetes clusters.

1

Create an Opaque secret YAML

Create a YAML file named opaque-secret.yaml that defines a Kubernetes secret of type Opaque named my-opaque-secret. Include the data fields username with value admin and password with value secret123. Use base64 encoding for the values.

Kubernetes

# Create a YAML file named opaque-secret.yaml with an Opaque secret
# Your code here

Hint

Use echo -n 'admin' | base64 and echo -n 'secret123' | base64 to get base64 encoded values.

2

Create a docker-registry secret YAML

Create a YAML file named docker-secret.yaml that defines a Kubernetes secret of type kubernetes.io/dockerconfigjson named my-docker-secret. Use the following Docker registry credentials encoded in base64 inside the .dockerconfigjson key: server https://index.docker.io/v1/, username dockeruser, password dockersecret, email [e-mail]. The .dockerconfigjson value must be a base64 encoded JSON string with these credentials.

Kubernetes

apiVersion: v1
kind: Secret
metadata:
  name: my-opaque-secret
type: Opaque
data:
  username: YWRtaW4=
  password: c2VjcmV0MTIz

# Create docker-secret.yaml with docker-registry secret
# Your code here

Hint

Prepare a JSON like {"auths":{"https://index.docker.io/v1/":{"username":"dockeruser","password":"dockersecret","email":"[e-mail]","auth":"ZG9ja2VydXNlcjpkb2NrZXJzZWNyZXQ="}}} and base64 encode it.

Replace dockerauth_token with base64 of dockeruser:dockersecret.

3

Create a TLS secret YAML

Create a YAML file named tls-secret.yaml that defines a Kubernetes secret of type kubernetes.io/tls named my-tls-secret. Use the keys tls.crt and tls.key with base64 encoded dummy certificate and key values: dummycert and dummykey respectively.

Kubernetes

apiVersion: v1
kind: Secret
metadata:
  name: my-opaque-secret
type: Opaque
data:
  username: YWRtaW4=
  password: c2VjcmV0MTIz
---
apiVersion: v1
kind: Secret
metadata:
  name: my-docker-secret
type: kubernetes.io/dockerconfigjson
data:
  .dockerconfigjson: eyJhdXRocyI6eyJodHRwczovL2luZGV4LmRvY2tlci5pby92MS8iOnsidXNlcm5hbWUiOiJkb2NrZXJ1c2VyIiwicGFzc3dvcmQiOiJkb2NrZXJzZWNyZXQiLCJlbWFpbCI6InVzZXJAZXhhbXBsZS5jb20iLCJhdXRoIjoiZG9ja2VyYXV0aF90b2tlbiJ9fX0=

# Create tls-secret.yaml with TLS secret
# Your code here

Hint

Base64 encode dummycert and dummykey using echo -n 'dummycert' | base64 and echo -n 'dummykey' | base64.

4

Apply and verify the secrets

Use kubectl apply -f to create the secrets from the YAML files opaque-secret.yaml, docker-secret.yaml, and tls-secret.yaml. Then, run kubectl get secrets my-opaque-secret my-docker-secret my-tls-secret -o yaml to display the secrets and verify their types and data keys.

Kubernetes

apiVersion: v1
kind: Secret
metadata:
  name: my-opaque-secret
type: Opaque
data:
  username: YWRtaW4=
  password: c2VjcmV0MTIz
---
apiVersion: v1
kind: Secret
metadata:
  name: my-docker-secret
type: kubernetes.io/dockerconfigjson
data:
  .dockerconfigjson: eyJhdXRocyI6eyJodHRwczovL2luZGV4LmRvY2tlci5pby92MS8iOnsidXNlcm5hbWUiOiJkb2NrZXJ1c2VyIiwicGFzc3dvcmQiOiJkb2NrZXJzZWNyZXQiLCJlbWFpbCI6InVzZXJAZXhhbXBsZS5jb20iLCJhdXRoIjoiZG9ja2VyYXV0aF90b2tlbiJ9fX0=
---
apiVersion: v1
kind: Secret
metadata:
  name: my-tls-secret
type: kubernetes.io/tls
data:
  tls.crt: ZHVtbXljZXJ0
  tls.key: ZHVtbXlrZXk=

# Apply all three secrets and verify their creation
# Your code here

Hint

Run kubectl apply -f for each YAML file, then kubectl get secrets with -o yaml to see details.

Practice

1. Which Kubernetes secret type is best suited for storing general sensitive data like passwords or tokens?

easy

A. Opaque

B. docker-registry

C. TLS

D. ConfigMap

Solution

1. Step 1: Understand secret types

   Opaque secrets are designed to store arbitrary user-defined data such as passwords or tokens.

2. Step 2: Compare with other types

   docker-registry is for Docker credentials, TLS is for certificates, and ConfigMap is not a secret type.

3. Final Answer:

   Opaque -> Option A

4. Quick Check:

   General sensitive data = Opaque [OK]

Hint: Opaque = general secret data, docker-registry = Docker creds [OK]

Common Mistakes:

• Confusing TLS secrets with general data storage
• Using docker-registry for non-Docker secrets
• Thinking ConfigMap is a secret type

2. Which kubectl command correctly creates a docker-registry secret named myregistrykey with username user1 and password pass123?

easy

A. kubectl create secret docker-registry myregistrykey --docker-server=https://myregistry.com --docker-username=user1 --docker-password=pass123

B. kubectl create secret generic myregistrykey --docker-username=user1 --docker-password=pass123

C. kubectl create secret tls myregistrykey --docker-username=user1 --docker-password=pass123

D. kubectl create secret docker-registry myregistrykey --username=user1 --password=pass123

Solution

1. Step 1: Identify correct secret type and flags

   docker-registry secrets require the type 'docker-registry' and flags --docker-server, --docker-username and --docker-password.

2. Step 2: Check command syntax

   kubectl create secret docker-registry myregistrykey --docker-server=https://myregistry.com --docker-username=user1 --docker-password=pass123 uses correct type and flags; others use wrong types or flag names.

3. Final Answer:

   kubectl create secret docker-registry myregistrykey --docker-server=https://myregistry.com --docker-username=user1 --docker-password=pass123 -> Option A

4. Quick Check:

   docker-registry + --docker-server/--docker-username/password = correct [OK]

Hint: Use --docker-server, --docker-username and --docker-password with docker-registry type [OK]

Common Mistakes:

• Using generic secret type for docker-registry secrets
• Wrong flag names like --username instead of --docker-username
• Using TLS secret type for docker credentials

3. Given the command kubectl create secret tls mytlssecret --cert=cert.pem --key=key.pem, what will be the type of the created secret?

medium

A. Opaque

B. docker-registry

C. TLS

D. generic

Solution

1. Step 1: Analyze the command

   The command uses 'create secret tls' with certificate and key files specified.

2. Step 2: Match secret type

   Secrets created with 'tls' type store TLS certificates and keys, so the type is TLS.

3. Final Answer:

   TLS -> Option C

4. Quick Check:

   kubectl create secret tls = TLS type secret [OK]

Hint: TLS secrets use 'kubectl create secret tls' with cert and key [OK]

Common Mistakes:

• Assuming TLS secrets are Opaque
• Confusing generic secret type with TLS
• Not specifying cert and key files properly

4. You run kubectl create secret tls mytlssecret --cert=cert.pem but get an error. What is the likely cause?

medium

A. Using wrong secret type, should be opaque

B. Missing --key flag with private key file

C. Certificate file is empty

D. Secret name contains invalid characters

Solution

1. Step 1: Check required flags for TLS secret

   Creating TLS secrets requires both --cert and --key flags to specify certificate and private key files.

2. Step 2: Identify missing flag

   The command only has --cert but lacks --key, causing the error.

3. Final Answer:

   Missing --key flag with private key file -> Option B

4. Quick Check:

   Both --cert and --key required for TLS secret [OK]

Hint: TLS secrets need both --cert and --key flags [OK]

Common Mistakes:

• Omitting the --key flag when creating TLS secrets
• Using opaque type instead of TLS for certs
• Assuming secret name format causes error

5. You want to pull images from a private Docker registry in your Kubernetes cluster. Which secret type should you create and how should you use it in a Pod spec?

hard

A. Create a TLS secret and add it to the Pod's environment variables

B. Create an opaque secret and mount it as a volume in the Pod

C. Create a generic secret and specify it in the Pod's volumes section

D. Create a docker-registry secret and reference it in imagePullSecrets of the Pod

Solution

1. Step 1: Identify secret type for private Docker registry

   docker-registry secret stores Docker credentials for private registries.

2. Step 2: Use secret in Pod spec

   To allow image pull, reference the secret in the Pod's imagePullSecrets field.

3. Final Answer:

   Create a docker-registry secret and reference it in imagePullSecrets of the Pod -> Option D

4. Quick Check:

   Private Docker registry = docker-registry secret + imagePullSecrets [OK]

Hint: Use docker-registry secret with imagePullSecrets in Pod spec [OK]

Common Mistakes:

• Mounting docker-registry secrets as volumes instead of imagePullSecrets
• Using opaque or TLS secrets for Docker registry auth
• Not referencing the secret in Pod spec