Secrets management in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is secrets management in Docker?

Secrets management in Docker is a way to securely store and manage sensitive data like passwords, API keys, and certificates so they are not exposed in your application code or Docker images.

beginner

How do you create a secret in Docker?

You create a secret in Docker using the command:

docker secret create <secret_name> <file_with_secret>

This stores the secret securely in the Docker swarm.

intermediate

How can a Docker service access a secret?

When you deploy a Docker service, you can attach secrets to it using the --secret flag. Inside the container, the secret is available as a file in /run/secrets/<secret_name>.

beginner

Why should secrets not be stored in Docker images or environment variables?

Storing secrets in images or environment variables risks exposing them because images can be shared and environment variables can be viewed by other processes or users. Docker secrets keep them encrypted and only available to authorized services.

intermediate

What happens to Docker secrets when a service is removed?

When a Docker service is removed, the secrets attached to it are no longer accessible by that service. Docker manages secrets lifecycle so they are only available to running services that need them.

Which command creates a Docker secret?

A docker secret create my_secret secret.txt

B docker create secret my_secret secret.txt

C docker secret add my_secret secret.txt

D docker secret new my_secret secret.txt

The correct syntax to create a secret is 'docker secret create <name> <file>'.

Where are Docker secrets available inside a container?

A /run/secrets/

B /etc/secrets/

C /var/lib/secrets/

D /usr/local/secrets/

Docker mounts secrets as files inside the container at /run/secrets/<secret_name>.

Why is it unsafe to store secrets in environment variables?

A They are encrypted automatically

B They can be viewed by other processes or users

C They are only accessible inside the container

D They expire after service removal

Environment variables can be exposed to other processes or users, risking secret leaks.

How do you attach a secret to a Docker service?

A Set the secret as an environment variable

B Add the secret to the Dockerfile

C Mount the secret as a volume

D Use the --secret flag during service creation

Secrets are attached to services using the --secret flag when creating or updating the service.

What happens to secrets when a Docker service is removed?

A Secrets are deleted from Docker swarm

B Secrets remain accessible to all containers

C Secrets are no longer accessible by that service

D Secrets are stored in environment variables

Secrets are only accessible to running services that have them attached; removing the service revokes access.

Explain how Docker secrets help keep sensitive data safe in your applications.

Think about how secrets avoid exposure compared to environment variables or image layers.

Describe the steps to create a secret and use it in a Docker service.

Start from creating the secret file, then how to add it to a service, and finally how the service reads it.

Practice

1. What is the main purpose of using docker secrets in a Docker environment?

easy

A. To securely store sensitive data like passwords outside of Docker images

B. To speed up container startup time

C. To increase the size of Docker images

D. To manage container networking settings

Solution

1. Step 1: Understand what secrets are

   Secrets are sensitive data such as passwords or keys that should not be stored inside images or code.

2. Step 2: Identify the purpose of Docker secrets

   Docker secrets provide a secure way to store and manage this sensitive data outside of images, making it available only to authorized services.

3. Final Answer:

   To securely store sensitive data like passwords outside of Docker images -> Option A

4. Quick Check:

   Secrets = Secure sensitive data storage [OK]

Hint: Secrets keep passwords safe outside images [OK]

Common Mistakes:

• Thinking secrets speed up containers
• Confusing secrets with networking
• Assuming secrets increase image size

2. Which of the following commands correctly creates a Docker secret named db_password from a file password.txt?

easy

A. docker secret create db_password password.txt

B. docker secret add db_password password.txt

C. docker secret new db_password password.txt

D. docker secret generate db_password password.txt

Solution

1. Step 1: Recall Docker secret creation syntax

   The correct command to create a secret is docker secret create [name] [file].

2. Step 2: Match the command with options

   docker secret create db_password password.txt matches the correct syntax exactly.

3. Final Answer:

   docker secret create db_password password.txt -> Option A

4. Quick Check:

   docker secret create = correct syntax [OK]

Hint: Use 'docker secret create' to add secrets from files [OK]

Common Mistakes:

• Using 'add' instead of 'create'
• Using 'new' or 'generate' which are invalid
• Confusing secret commands with service commands

3. Given the following Docker service creation command:

docker service create --name myapp --secret db_password nginx

What happens to the secret db_password inside the running container?

medium

A. It is stored as an environment variable named DB_PASSWORD

B. It is printed in the container logs

C. It is mounted as a file in /run/secrets/db_password

D. It is embedded inside the container image

Solution

1. Step 1: Understand how Docker secrets are exposed

   Docker secrets are mounted as files inside the container at /run/secrets/[secret_name].

2. Step 2: Analyze the options

   It is mounted as a file in /run/secrets/db_password correctly states the secret is mounted as a file. Options A, B, and D are incorrect because secrets are not environment variables, not printed in logs, and not embedded in images.

3. Final Answer:

   It is mounted as a file in /run/secrets/db_password -> Option C

4. Quick Check:

   Secrets = files in /run/secrets [OK]

Hint: Secrets appear as files in /run/secrets inside containers [OK]

Common Mistakes:

• Thinking secrets become environment variables automatically
• Expecting secrets to be logged
• Assuming secrets are inside the image

4. You run docker secret create mysecret secret.txt but get an error: Error: secret file secret.txt not found. What is the most likely cause?

medium

A. The secret already exists

B. The file secret.txt does not exist in the current directory

C. Docker daemon is not running

D. You used the wrong secret name

Solution

1. Step 1: Understand the error message

   The error says the file secret.txt was not found, meaning Docker cannot locate the file to create the secret.

2. Step 2: Identify the cause

   This usually means the file is missing or the path is incorrect. The file secret.txt does not exist in the current directory matches this cause. Other options do not relate to file not found errors.

3. Final Answer:

   The file secret.txt does not exist in the current directory -> Option B

4. Quick Check:

   File missing = secret create error [OK]

Hint: Check file path exists before creating secret [OK]

Common Mistakes:

• Assuming secret name causes file error
• Ignoring Docker daemon status
• Thinking secret existence causes file not found

5. You want to update a secret api_key used by a running Docker service webapp. Which sequence of commands correctly updates the secret without downtime?

hard

A. Edit the secret file inside the running container

B. Directly overwrite the existing secret with docker secret update

C. Stop the service, delete the secret, create new secret with same name, then start service

D. Create new secret with a different name, update service to use new secret, then remove old secret

Solution

1. Step 1: Understand Docker secret immutability

   Docker secrets cannot be updated directly; they are immutable once created.

2. Step 2: Update secret safely

   The recommended way is to create a new secret with a new name, update the service to use this new secret, then remove the old secret to avoid downtime.

3. Step 3: Analyze options

   Create new secret with a different name, update service to use new secret, then remove old secret follows this process. Directly overwrite the existing secret with docker secret update is invalid because docker secret update does not exist. Stop the service, delete the secret, create new secret with same name, then start service causes downtime. Edit the secret file inside the running container is impossible because secrets are mounted read-only.

4. Final Answer:

   Create new secret with a different name, update service to use new secret, then remove old secret -> Option D

5. Quick Check:

   Secrets immutable = create new and update service [OK]

Hint: Create new secret and update service to avoid downtime [OK]

Common Mistakes:

• Trying to overwrite existing secret
• Stopping service causing downtime
• Editing secrets inside container