COPY and ADD
- Docker & Kubernetes course
- Beginner
- Lesson 22/82
- 4 min
Learn to copy files into an image with COPY.
COPY and ADD
COPY source destination copies files from the build context (usually the project folder) into the image. If the destination ends with / it is a directory; if WORKDIR is set, a relative path is resolved against it:
WORKDIR /app
COPY requirements.txt . # /app/requirements.txt
COPY src/ ./src/ # copy a folder
COPY --chown=node:node . . # set ownershipWhy the dependency file first?
Copying the dependency list separately before the source code uses the cache well: when the code changes only the last layers are rebuilt, and the long package installation comes from the cache:
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt # runs only when requirements change
COPY . . # only this layer when the code changesPractice Cache-friendly copying
Write a Dockerfile based on python:3.12-slim with WORKDIR /app: first copy requirements.txt, run pip install --no-cache-dir -r requirements.txt, then copy the whole project.
Starter code
# buraya yazSample solution
FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .Expected output
[+] Building 4.2s (8/8) FINISHED => naming to docker.io/library/api:latest done
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does ADD do that COPY doesn't?
- It only copies folders
- It extracts local tar archives and can download from URLs Correct answer
- It deletes files
- It copies faster
Explanation: Because these "magic" behaviours cause surprises, COPY is preferred.
2 Set the owner of the copied files.
COPY ____=node:node . .COPY --chown=node:node . .Explanation: --chown takes user:group.
3 Match.
| Term | Meaning |
|---|---|
COPY |
Copies from the context |
ADD |
Extracts tar, downloads URLs |
COPY . . |
Copies the whole project |
requirements.txt first |
Cache-friendly order |