COPY instruction for adding files in Docker - Step-by-Step Execution

Process Flow - COPY instruction for adding files

Start Dockerfile

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Read COPY instruction

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Locate source files on host

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Copy files into image at destination

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Continue building image

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Image ready with copied files

The Dockerfile COPY instruction reads source files from your computer and copies them into the image at the specified destination path.

Execution Sample

Docker

COPY ./app /usr/src/app
RUN ls /usr/src/app

Copies the local 'app' folder into the image at '/usr/src/app' and lists its contents.

Process Table

Step	Instruction	Action	Source Path	Destination Path	Result
1	COPY ./app /usr/src/app	Locate and copy files	./app	/usr/src/app	Files copied into image
2	RUN ls /usr/src/app	List files	-	/usr/src/app	Shows copied files
3	-	Build complete	-	-	Image contains /usr/src/app with copied files

💡 COPY completes when all source files are copied to destination inside the image

Status Tracker

Variable	Start	After COPY	After RUN	Final
/usr/src/app contents	empty	files from ./app copied	listed files	files present in image

Key Moments - 3 Insights

Why does COPY fail if the source path is wrong?

COPY looks for files on the host at the exact source path. If the path is wrong, no files are found to copy, so the build fails (see execution_table step 1).

Does COPY preserve file permissions?

Yes, COPY preserves file permissions and metadata when copying files into the image, so files behave as expected inside the container.

Can COPY copy files from URLs or remote locations?

No, COPY only copies files from the local build context (your computer). To get files from URLs, use RUN with curl or wget.

Visual Quiz - 3 Questions

Look at the execution table, what is the source path used in the COPY instruction?

A /app

B ./app

C /usr/src/app

D ./usr/src/app

💡 Hint

Check the 'Source Path' column in execution_table row 1

At which step does the image contain the copied files?

A After build finishes

B Step 2

C Step 1

D Step 3

💡 Hint

Look at the 'Result' column in execution_table rows 1 to 3

If the source path is incorrect, what happens to the build?

A Build continues without copying files

B Files are copied from a default location

C Build fails at COPY step

D COPY instruction is skipped

💡 Hint

Refer to key_moments about COPY failure and execution_table step 1

Concept Snapshot

COPY instruction syntax:
COPY <source_path> <destination_path>
Copies files/folders from local build context into image.
Source path must be relative to build context.
Preserves file permissions.
Fails if source path not found.

Full Transcript

The COPY instruction in Dockerfile copies files from your computer into the image. It reads the source path on your host machine and copies those files into the destination path inside the image. If the source path is wrong, the build fails. After copying, the files are available inside the image at the destination path. This is useful to add your app code or configuration files into the container image.