Docker - Difference between COPY and ADD in Dockerfile

COPY and ADD are both Dockerfile instructions that does similar operation. Both instructions are used to copy files into a Docker image. Let's look at some use cases for both.

COPY instruction in a Dockerfile

• The COPY instruction copies files or directories into the Docker image.
• It takes a src and destination as arguments.
• Source can be absolute or relative from current WORKDIR or wild cards.
• Destination path can be absolute or relative to current WORKDIR.

Examples:

COPY ./requirements.txt /app/requirements.txt 
COPY package.json package-lock.json /app
COPY package*.json /app
COPY . /app

Using COPY instruction to add source code into Docker Image

FROM python:3.8.0

# set working directory
WORKDIR /app

# add requirements
COPY ./requirements.txt /app/requirements.txt

# install requirements
RUN pip install -r requirements.txt

# copy source code to /app
COPY . /app

# run server
CMD python main.py

# expose 
EXPOSE 5000

ADD instruction in a Dockerfile

• The ADD instruction copies files, directories, remote file or tar archive into the Docker image.
• It takes a src and destination as arguments.
• Source can be files and directories.
• Source can be a URL. The ADD instruction will download the file from the URL and save it to the destination. We don't need to use curl or wget to download a file.
• Source can be a local tar/zip archive. The ADD instruction will automatically extract it to the destion. We don't need to run unarchive commands manually.
• Use ADD when you want download a file from a URL or extract local archive file.

ADD ./example.tar.gz /tmp/

ADD https://bootstrap.pypa.io/get-pip.py /get-pip.py

Using ADD instruction to update pip package manager

FROM python:3.8.0

# set working directory
WORKDIR /app

# add requirements
COPY ./requirements.txt /app/requirements.txt

# updating pip
ADD https://bootstrap.pypa.io/get-pip.py /get-pip.py
RUN python /get-pip.py

# install requirements
RUN pip install -r requirements.txt

# add source code
COPY . /app

# run server
CMD python main.py

# expose 
EXPOSE 5000

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