Where Should You Place .dockerignore? Best Practices for Docker Builds

When working with Docker, placing your .dockerignore file in the right location is crucial for optimizing builds and improving security. Many developers wonder: should .dockerignore be in the same location as the Dockerfile? The short answer is yes, but with some considerations.

📌 Understanding the Docker Build Context

The build context is the directory that Docker uses when running docker build. It includes all files and subdirectories unless explicitly excluded using .dockerignore.

docker build -t my-image:latest /path/to/build-context

In this command:

• /path/to/build-context is the build context.
• Docker will reference the .dockerignore file inside this directory.
• If a .dockerignore file is present, Docker will exclude listed files from the build context, reducing image size and improving security.

🗂 Where to Place .dockerignore?

The .dockerignore file should be placed in the root of your build context—not necessarily next to the Dockerfile.

✔️ Typical Case: Dockerfile and .dockerignore in the Same Directory

If your Dockerfile is inside the build context directory, keep .dockerignore in the same location:

/project-root
│
├── Dockerfile
├── .dockerignore
├── src/
│   └── main.js
└── package.json

Run the build command from /project-root:

docker build -t my-image:latest .

✅ Docker will correctly apply .dockerignore to exclude unnecessary files.

⚠️ Special Case: Dockerfile in a Different Directory

If your Dockerfile is not inside the build context, Docker still looks for .dockerignore in the build context directory.

For example:

docker build -f /path/to/Dockerfile /path/to/build-context

Here:

• -f specifies the location of the Dockerfile.
• /path/to/build-context is the build context, so .dockerignore must be placed inside this directory, not with Dockerfile.

❌ Wrong Structure (Will Not Work as Expected):

/path/to/
│
├── Dockerfile
│
└── build-context/
    ├── .dockerignore  ❌ (Ignored if build context is incorrect)
    ├── src/
    ├── package.json

🚨 Docker will not use .dockerignore if the wrong directory is specified as the build context!

🛠 Best Practices for .dockerignore Placement

✅ Align Dockerfile with Build Context

• To simplify builds, keep your Dockerfile inside the root of your build context.

✅ Always Define the Build Context Explicitly

• When running docker build, clearly specify the build context directory.

✅ Keep .dockerignore in the Build Context

• This ensures that Docker excludes unnecessary files from being sent to the daemon.

✅ Exclude Unnecessary Files

• Use .dockerignore to remove large files, secrets, and unused directories:

node_modules
.git
.env
logs/
dist/

🔹 Example: Correct .dockerignore Placement

Given the following structure:

/my-app
│
├── Dockerfile
├── .dockerignore
├── src/
│   └── main.js
└── package.json

Run:

docker build -t my-image:latest .

💡 Docker will correctly exclude files listed in .dockerignore, ensuring a smaller and more secure image.

🚀 Conclusion

• Keep .dockerignore in the root of your build context.
• Ensure your build context is set correctly when using docker build.
• Using .dockerignore properly reduces image size and prevents security risks.

By following these best practices, you’ll optimize Docker builds and avoid unnecessary complications. 🚀

Have you encountered .dockerignore issues in your builds? Share your experience in the comments!