Docker deployment in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Docker in simple terms?

Docker is like a shipping container for software. It packages your app and everything it needs so it runs the same anywhere.

beginner

Why use Docker for deploying a Svelte app?

Docker makes sure your Svelte app runs the same on your computer and on any server, avoiding "it works on my machine" problems.

beginner

What is a Dockerfile?

A Dockerfile is a simple text file with instructions to build a Docker image. It tells Docker how to prepare your app's container.

intermediate

In Docker deployment, what is an image vs a container?

An image is a blueprint with your app and setup. A container is a running instance of that image, like a live copy.

intermediate

How do you expose your Svelte app's port in Docker?

You use the EXPOSE command in the Dockerfile and map the port when running the container with -p, so the app is reachable.

What command builds a Docker image from a Dockerfile?

A docker build

B docker run

C docker start

D docker push

The 'docker build' command reads the Dockerfile and creates an image.

Which file typically contains instructions to create a Docker image for a Svelte app?

A Dockerfile

B package.json

C svelte.config.js

D index.html

Dockerfile contains the step-by-step instructions to build the Docker image.

How do you make your Svelte app accessible outside the Docker container?

A Run npm start inside the container

B Add a script in package.json

C Use a different framework

D Use EXPOSE in Dockerfile and map ports with -p

EXPOSE declares the port, and -p maps it to the host so you can access the app.

What does the command 'docker run -p 5000:5000 my-svelte-app' do?

A Deletes the Docker image

B Runs the container and maps port 5000 inside to port 5000 outside

C Stops the running container

D Builds the Docker image

It runs the container and connects the internal port 5000 to your computer's port 5000.

Why is Docker helpful for beginners deploying Svelte apps?

A It replaces the need for HTML

B It hides all code details

C It ensures the app runs the same everywhere

D It automatically writes your app

Docker packages your app so it behaves the same on any computer or server.

Explain how you would create a Dockerfile to deploy a Svelte app.

Think about the steps to prepare and run your app inside a container.

Describe the difference between a Docker image and a Docker container in your own words.

Compare it to a cake recipe versus a baked cake.

Practice

1. What is the main purpose of using Docker for deploying a Svelte app?

easy

A. To automatically fix bugs in the app

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

C. To make the app load faster in the browser

D. To write the app code faster

Solution

1. Step 1: Understand Docker's role

   Docker creates a container that holds your app and all its parts, so it works the same everywhere.

2. Step 2: Compare options

   Only To package the app so it runs the same on any machine describes this packaging and consistency purpose. Others talk about coding speed, browser speed, or bug fixing, which Docker does not do.

3. Final Answer:

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

4. Quick Check:

   Docker ensures consistent app environment = D [OK]

Hint: Docker packages apps for consistent environments [OK]

Common Mistakes:

• Thinking Docker speeds up coding
• Confusing Docker with browser performance tools
• Assuming Docker fixes app bugs automatically

2. Which line correctly exposes port 3000 in a Dockerfile for a Svelte app?

easy

A. EXPOSE 3000

B. EXPOSE:3000

C. EXPOSE = 3000

D. EXPOSE_PORT 3000

Solution

1. Step 1: Recall Dockerfile syntax for ports

   The correct syntax to expose a port is simply 'EXPOSE' followed by the port number without symbols.

2. Step 2: Check each option

   Only 'EXPOSE 3000' matches the correct syntax. Others have invalid characters or wrong commands.

3. Final Answer:

   EXPOSE 3000 -> Option A

4. Quick Check:

   Correct Dockerfile port syntax = B [OK]

Hint: Use 'EXPOSE' followed by port number without symbols [OK]

Common Mistakes:

• Adding colons or equals signs after EXPOSE
• Using wrong command names like EXPOSE_PORT
• Forgetting to expose the port at all

3. Given this Dockerfile snippet for a Svelte app:

FROM node:18-alpine
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
RUN npm run build
EXPOSE 3000
CMD ["npm", "run", "preview"]

What happens when you run this container?

medium

A. The app builds and runs on port 3000 serving the preview

B. The app fails because 'npm run preview' is invalid

C. The container exposes port 80 instead of 3000

D. The app runs but does not build before starting

Solution

1. Step 1: Analyze Dockerfile commands

   The Dockerfile installs dependencies, copies files, builds the app, exposes port 3000, and runs 'npm run preview' which serves the built app.

2. Step 2: Understand container behavior

   Since 'npm run preview' is the correct command to serve a Svelte build, the app will run on port 3000 as exposed.

3. Final Answer:

   The app builds and runs on port 3000 serving the preview -> Option A

4. Quick Check:

   Build then preview on port 3000 = A [OK]

Hint: Check build then preview commands and exposed port [OK]

Common Mistakes:

• Assuming 'npm run preview' is invalid
• Confusing exposed port 3000 with 80
• Thinking build step is missing

4. You wrote this Dockerfile for your Svelte app but the container fails to start:

FROM node:18-alpine
WORKDIR /app
COPY . .
RUN npm install
RUN npm run build
EXPOSE 3000
CMD npm run preview

What is the likely error?

medium

A. npm install should come after build

B. EXPOSE 3000 is missing

C. CMD should be an array, not a string

D. WORKDIR is not set

Solution

1. Step 1: Check CMD syntax in Dockerfile

   CMD should be an array of strings like ["npm", "run", "preview"] to run correctly in Docker.

2. Step 2: Verify other parts

   EXPOSE 3000 is present, npm install is before build which is correct, and WORKDIR is set. So these are not errors.

3. Final Answer:

   CMD should be an array, not a string -> Option C

4. Quick Check:

   Use array syntax for CMD = A [OK]

Hint: Use array syntax for CMD in Dockerfile [OK]

Common Mistakes:

• Writing CMD as a plain string
• Changing order of npm install and build incorrectly
• Forgetting to set WORKDIR

5. You want to deploy a Svelte app with Docker but need to serve it on port 8080 instead of 3000. Which change in the Dockerfile is correct?

FROM node:18-alpine
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
RUN npm run build
EXPOSE 3000
CMD ["npm", "run", "preview"]

hard

A. Change CMD to ["npm", "run", "preview", "--port", "8080"] only

B. Only change EXPOSE 3000 to EXPOSE 8080

C. No changes needed; Docker maps ports automatically

D. Change EXPOSE 3000 to EXPOSE 8080 and run preview with PORT=8080

Solution

1. Step 1: Understand port exposure and app config

   Changing EXPOSE alone only tells Docker which port to open, but the app must also listen on that port.

2. Step 2: Set app to listen on port 8080

   You must pass the PORT environment variable or argument so 'npm run preview' serves on port 8080.

3. Step 3: Combine both changes

   Change EXPOSE to 8080 and run preview with PORT=8080 ensures Docker and app ports match.

4. Final Answer:

   Change EXPOSE 3000 to EXPOSE 8080 and run preview with PORT=8080 -> Option D

5. Quick Check:

   Match exposed port and app port = C [OK]

Hint: Match Docker EXPOSE and app port settings [OK]

Common Mistakes:

• Changing only EXPOSE without app port
• Changing only CMD without exposing port
• Assuming Docker auto-maps ports