When building Docker images, one common stumbling block involves the COPY instruction. The error message "no such file or directory" typically stems from a fundamental misunderstanding of Docker's build context. Let's examine why the original approach failed:

# Problematic approach (won't work)
COPY /srv/visitor /srv/visitor

This fails because Docker's COPY command only works within the build context - the directory where you run docker build from.

The build context includes all files and directories in the current directory (and subdirectories) when you execute:

docker build -t myapp .

The dot (.) represents the build context. Any files outside this directory are inaccessible during the build process.

The proper approach involves either:

# Option 1: Copy from build context
COPY . /srv/visitor

# Option 2: Copy specific files
COPY package.json visitor.js /srv/visitor/

The subsequent npm install failure occurs because:

1. The working directory in the container might not be /srv/visitor
2. The files might not have been copied to the expected location

Here's a complete working example:

FROM node:14

# Set working directory
WORKDIR /srv/visitor

# Copy package.json first for better layer caching
COPY package.json .

# Install dependencies
RUN npm install

# Copy remaining files
COPY . .

# Application port
EXPOSE 3000

# Run application
CMD ["node", "visitor.js"]

To debug COPY operations:

# Check what files were actually copied
docker build -t myapp .
docker run -it myapp ls -la /srv/visitor

# Alternative: use multi-stage build for inspection
FROM alpine as debug
COPY --from=build-stage /srv/visitor /debug
RUN ls -la /debug

For more complex scenarios:

• Use .dockerignore to exclude unnecessary files
• Consider using bind mounts for development (docker run -v $(pwd):/srv/visitor)
• For production, ensure all required files are properly included in the build context

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When working with Docker's COPY instruction, one of the most common mistakes developers make is misunderstanding the build context. The error message "no such file or directory" often appears even when the files exist on your host system because Docker doesn't look at absolute paths the way you might expect.

The Docker build process only has access to files within the build context - the directory you specify when running docker build. When you use:

COPY /srv/visitor /srv/visitor

Docker looks for /srv/visitor relative to your build context, not from the root of your host filesystem. This explains why you're getting the "no such file" error despite the directory existing.

Here's how you should structure your Dockerfile and build command:

# Dockerfile
FROM node:latest
WORKDIR /srv/visitor
COPY . .
RUN npm install
CMD ["node", "visitor.js"]

Then build with:

docker build -t myapp /srv/visitor

The key points:

• The build context (/srv/visitor) is specified in the build command
• COPY uses relative paths from this context
• WORKDIR sets the container's working directory

The subsequent npm error occurs because either:

1. The files weren't copied as expected (verify with docker run -it image_name ls /srv/visitor)
2. The WORKDIR wasn't set before running npm install

A more robust version would be:

FROM node:latest
RUN mkdir -p /srv/visitor
WORKDIR /srv/visitor
COPY package.json .
RUN npm install
COPY . .
CMD ["node", "visitor.js"]

This approach:

• Creates the target directory explicitly
• Copies package.json first for layer caching benefits
• Only copies the rest after npm install

To debug whether files were copied correctly:

# Build with a name
docker build -t myapp .

# Run a temporary container to inspect
docker run --rm -it myapp ls -la /srv/visitor

This should show you exactly what made it into the container.

To prevent copying unwanted files (like node_modules) and potentially masking your actual files:

# .dockerignore
node_modules/
.git/
*.log

This ensures only your source files are copied while maintaining clean builds.