.dockerignore file
- The .dockerignore File: Optimizing Your MediaWiki Docker Builds
This article explains the purpose and usage of the `.dockerignore` file when building Docker images for your MediaWiki installation. Properly configuring this file is crucial for efficient build times and smaller image sizes, ultimately improving the performance and maintainability of your MediaWiki server. This guide is aimed at newcomers to Docker and MediaWiki server administration.
== What is the .dockerignore File?
The `.dockerignore` file functions similarly to a `.gitignore` file used in Git version control. It tells the Docker build process which files and directories to exclude from the build context. The build context is the set of files that are sent to the Docker daemon to build the image. Including unnecessary files in the build context can significantly increase build times and the final image size.
By strategically excluding files like temporary build artifacts, local development tools, and sensitive information, you can streamline the build process and create a more secure and efficient MediaWiki Docker image. Without a `.dockerignore` file, *everything* in the directory where you run `docker build` is sent to the daemon.
== Why is .dockerignore Important for MediaWiki?
MediaWiki installations often include a significant number of files that are not required within the production Docker image. These can include:
- Developer tools (e.g., IDE configuration files)
- Local configuration files (e.g., `LocalSettings.php` with database credentials—*never* include sensitive data in your image!)
- Temporary build files (e.g., compilation outputs)
- Version control system files (e.g., `.git` directory)
- Large media files that are served separately (e.g., through a dedicated media server or cloud storage)
Including these files in the build context wastes time and resources. A well-crafted `.dockerignore` file will address these issues. Also, consider using a Load Balancer to improve scalability.
== Creating and Configuring Your .dockerignore File
The `.dockerignore` file is a simple text file placed in the same directory as your `Dockerfile`. Each line in the file represents a pattern to exclude. Docker supports glob patterns, similar to those used in shell wildcards.
Here are some common patterns:
- `*`: Matches any file or directory.
- `?`: Matches a single character.
- `[abc]`: Matches any of the characters within the brackets.
- `**/`: Matches directories recursively.
- `!` : Negates a pattern (includes a file that would otherwise be excluded).
== Example .dockerignore File for a MediaWiki Installation
Here's an example `.dockerignore` file tailored for a typical MediaWiki Docker setup. Note that you'll need to adjust this based on your specific project structure.
| Pattern | Description |
|---|---|
| .git/ | Excludes the entire Git repository. |
| node_modules/ | Excludes Node.js dependencies if you are using any build tools like webpack. |
| vendor/ | Excludes composer dependencies, often large. |
| LocalSettings.php | Excludes local configuration. *Crucially important for security!* |
| config/ | Excludes any other local configuration directories. |
| tmp/ | Excludes temporary files. |
| logs/ | Excludes log files. |
| *.log | Excludes all log files. |
| **/tests/ | Excludes all test directories recursively. |
| .DS_Store | Excludes macOS Finder metadata files. |
It's important to remember that the order of patterns in `.dockerignore` matters. Later patterns can override earlier ones. Using `!` can be useful for re-including files that were previously excluded by a broader pattern. Consider using a Reverse Proxy for additional security.
== Advanced .dockerignore Techniques
You can use more complex patterns to fine-tune your exclusions. For instance, you can exclude specific files within a directory while including others.
Consider this scenario: you have a directory called `images` containing both necessary and unnecessary images. You only want to include the images in the `images/production` subdirectory. Your `.dockerignore` file could look like this:
| Pattern | Description |
|---|---|
| images/* | Excludes all files and directories within `images/`. |
| !images/production/ | Re-includes the `images/production/` directory and its contents. |
| !images/production/* | Re-includes all files within `images/production/` |
This ensures that only the production images are included in the Docker image. Using a Database Cluster can also improve performance.
== Best Practices and Troubleshooting
- **Start simple:** Begin with a basic `.dockerignore` file excluding only the most obvious unnecessary files.
- **Test incrementally:** Add patterns one at a time and rebuild your image to verify that the exclusions are working as expected. Check the image size after each change.
- **Be specific:** Avoid overly broad patterns that might exclude important files.
- **Use version control:** Commit your `.dockerignore` file to your version control system along with your `Dockerfile` to ensure consistency.
- **Check your Dockerfile:** Ensure your `Dockerfile` isn't explicitly copying files that you're trying to ignore in `.dockerignore`. Conflicts will result in unexpected behavior.
- **Cache Busting:** If you are making changes to files included in the build context, but the Docker build isn't reflecting those changes, it might be due to Docker caching. You can force a rebuild by adding the `--no-cache` flag to your `docker build` command. Consider using a Content Delivery Network (CDN) to accelerate media delivery.
== Technical Specifications
Here's a summary of key technical aspects related to `.dockerignore`:
| Specification | Detail |
|---|---|
| File Location | Same directory as the `Dockerfile` |
| Pattern Syntax | Glob patterns (similar to shell wildcards) |
| Pattern Processing | Processed sequentially, with later patterns potentially overriding earlier ones. |
| Negation | `!` character negates a pattern. |
| Recursive Matching | `**/` matches directories recursively. |
== Resources
- Docker Documentation on .dockerignore: [1](https://docs.docker.com/engine/reference/builder/#ignore-files)
- MediaWiki Official Website: [2](https://www.mediawiki.org/wiki/MediaWiki)
- Docker Hub: [3](https://hub.docker.com/)
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