Docker deployment for Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Docker used for in Deno deployment?

Docker packages your Deno app and its environment into a container. This makes it easy to run your app anywhere without setup problems.

beginner

What base image is commonly used for Deno in Dockerfiles?

The official Deno image like denoland/deno:latest is used as a base. It has Deno pre-installed and ready to run your app.

intermediate

Why do we copy only necessary files into the Docker image for Deno?

Copying only needed files keeps the image small and fast. It avoids including unnecessary files that slow down building and running.

beginner

How do you expose a port in a Dockerfile for a Deno app?

Use the EXPOSE instruction with the port number your Deno app listens on, e.g., EXPOSE 8000. This tells Docker which port to open.

beginner

What command runs the Deno app inside the Docker container?

The CMD instruction runs the app, for example: CMD ["deno", "run", "--allow-net", "app.ts"]. It starts your Deno script with needed permissions.

Which Docker base image is best for running a Deno app?

A denoland/deno:latest

B node:latest

C python:3.12

D ubuntu:latest

The official Deno image denoland/deno:latest includes Deno pre-installed, making it ideal for Deno apps.

What does the EXPOSE instruction do in a Dockerfile?

A Runs the app inside the container

B Copies files into the container

C Specifies which port the container listens on

D Sets environment variables

EXPOSE tells Docker which port your app will use, so it can be accessed from outside.

Why should you keep your Docker image small when deploying Deno apps?

A To use more disk space

B To reduce build time and improve startup speed

C To make the app run slower

D To increase network traffic

Smaller images build faster and start quicker, making deployment smoother.

Which command starts a Deno app with network access inside Docker?

A deno run --allow-net app.ts

B node app.js

C python app.py

D deno start app.ts

Deno requires explicit permissions like --allow-net to access the network.

What is the purpose of the CMD instruction in a Dockerfile?

A To set environment variables

B To copy files into the container

C To expose ports

D To specify the command to run when the container starts

CMD defines the default command that runs when the container launches.

Explain the steps to create a Dockerfile for deploying a Deno app.

Think about base image, files, ports, and run command.

Why is Docker useful for deploying Deno applications in different environments?

Consider how Docker containers work like a box with everything inside.

Practice

1. What is the main purpose of using Docker for deploying a Deno application?

easy

A. To replace the Deno runtime

B. To write Deno code faster

C. To package the app so it runs the same on any machine

D. To debug Deno code inside the browser

Solution

1. Step 1: Understand Docker's role

   Docker packages apps with all dependencies so they run consistently anywhere.

2. Step 2: Relate to Deno deployment

   Using Docker for Deno ensures the app runs the same on any machine without setup issues.

3. Final Answer:

   To package the app so it runs the same on any machine -> Option C

4. Quick Check:

   Docker packages apps = To package the app so it runs the same on any machine [OK]

Hint: Docker ensures consistent app environment everywhere [OK]

Common Mistakes:

• Thinking Docker speeds up coding
• Confusing Docker with Deno runtime
• Assuming Docker is for debugging only

2. Which Dockerfile instruction correctly sets the command to run a Deno script named app.ts with all permissions?

easy

A. CMD ["deno", "run", "--allow-all", "app.ts"]

B. RUN deno run --allow-all app.ts

C. ENTRYPOINT deno app.ts

D. CMD deno start app.ts

Solution

1. Step 1: Identify correct Dockerfile command syntax

   CMD with JSON array syntax is preferred for commands with arguments.

2. Step 2: Match Deno run command with permissions

   "deno run --allow-all app.ts" runs the script with all permissions; CMD array syntax is correct.

3. Final Answer:

   CMD ["deno", "run", "--allow-all", "app.ts"] -> Option A

4. Quick Check:

   Use CMD with JSON array for run command [OK]

Hint: Use CMD with JSON array for Deno run commands [OK]

Common Mistakes:

• Using RUN instead of CMD for runtime command
• Omitting --allow-all permission flag
• Using ENTRYPOINT without arguments array

3. Given this Dockerfile snippet:

FROM denoland/deno:latest
WORKDIR /app
COPY . .
RUN deno cache app.ts
CMD ["deno", "run", "--allow-net", "app.ts"]

What happens when you build and run this container?

medium

A. The app runs with network access allowed

B. The app runs but without network access

C. The container build fails due to missing permissions

D. The app runs but caching is skipped

Solution

1. Step 1: Analyze Dockerfile commands

   The Dockerfile caches dependencies with "deno cache app.ts" and runs the app with "--allow-net" permission.

2. Step 2: Understand runtime behavior

   CMD runs the app allowing network access, so the app can use network features.

3. Final Answer:

   The app runs with network access allowed -> Option A

4. Quick Check:

   --allow-net enables network access = The app runs with network access allowed [OK]

Hint: Check permission flags in CMD to know app access [OK]

Common Mistakes:

• Confusing cache step with runtime permissions
• Assuming build fails without --allow-all
• Ignoring the effect of --allow-net flag

4. You wrote this Dockerfile:

FROM denoland/deno:latest
WORKDIR /app
COPY . .
CMD ["deno", "run", "app.ts"]

But when running the container, the app crashes with permission errors. What is the fix?

medium

A. Remove COPY command

B. Change WORKDIR to /usr/src/app

C. Use RUN instead of CMD for deno run

D. Add permission flags like --allow-net to the CMD

Solution

1. Step 1: Identify cause of permission errors

   Deno requires explicit permission flags to access resources like network or file system.

2. Step 2: Fix Dockerfile CMD to include permissions

   Add flags like --allow-net or --allow-read to CMD so app has needed permissions at runtime.

3. Final Answer:

   Add permission flags like --allow-net to the CMD -> Option D

4. Quick Check:

   Permission errors need flags in CMD [OK]

Hint: Add needed --allow-* flags to CMD to fix permission errors [OK]

Common Mistakes:

• Changing WORKDIR without cause
• Removing COPY which copies app files
• Using RUN instead of CMD for runtime command

5. You want to optimize your Deno Docker image by caching dependencies to speed up builds. Which Dockerfile sequence achieves this best?

hard

A. COPY . .
RUN deno cache app.ts
CMD ["deno", "run", "--allow-all", "app.ts"]

B. COPY deps.ts ./
RUN deno cache deps.ts
COPY . .
CMD ["deno", "run", "--allow-all", "app.ts"]

C. RUN deno cache app.ts
COPY . .
CMD ["deno", "run", "app.ts"]

D. COPY app.ts ./
CMD ["deno", "run", "app.ts"]

Solution

1. Step 1: Understand Docker layer caching

   Docker caches layers; caching dependencies separately avoids re-downloading on code changes.

2. Step 2: Analyze COPY deps.ts ./ RUN deno cache deps.ts COPY . . CMD ["deno", "run", "--allow-all", "app.ts"]

   Copying only deps.ts and caching it first means dependencies are cached unless deps.ts changes, then copying rest avoids rebuilding cache.

3. Step 3: Compare other options

   Options A and C copy all files before caching, so cache invalidates on any file change; D lacks caching step.

4. Final Answer:

   COPY deps.ts ./ RUN deno cache deps.ts COPY . . CMD ["deno", "run", "--allow-all", "app.ts"] -> Option B

5. Quick Check:

   Cache deps separately for faster rebuilds [OK]

Hint: Cache dependencies before copying app code to speed builds [OK]

Common Mistakes:

• Copying all files before caching dependencies
• Skipping deno cache step
• Not using permission flags in CMD