Before we learn about multistage docker file, first we understand the concept of distroless image.
What is distroless image ?
A distroless image is a Docker image that contains only the necessary runtime dependencies for running an application and nothing else. Distroless images are minimal and do not contain any operating system package managers or shells, making them more secure and lightweight than traditional Linux-based images.
Distroless images are typically used for running containerized applications in production environments where security is a top priority. By removing unnecessary components from the image, distroless images minimize the attack surface and reduce the risk of vulnerabilities.
Instead of including a full operating system, distroless images rely on a base image that provides only the runtime environment for the application. The base image can be any lightweight image, such as Alpine Linux or Scratch.
Distroless images are created using Google's Distroless project, which provides pre-built images for a variety of programming languages, including Python, Java, Node.js, and Golang. The Distroless project is maintained by Google and is designed to be used with container orchestration platforms such as Kubernetes and Docker Swarm.
Mutlistage docker file
A multistage Dockerfile is a Dockerfile that includes multiple build stages to create a final Docker image. It is a technique that allows you to create a smaller Docker image by reducing the number of layers and removing unnecessary files and dependencies.
The first stage of a multistage Dockerfile usually includes building the application or compiling the source code. Once the build process is complete, the final Docker image is created in the second stage. This stage only includes the files and dependencies required to run the application.
The advantage of using a multistage Dockerfile is that it helps reduce the size of the final Docker image by eliminating intermediate layers and files that are not required in the final image. This results in a smaller image size, faster build times, and improved security since there are fewer attack surfaces.
Here's an example of a multistage Dockerfile for a Python application:
# Build stage
FROM python:3.9 AS build
WORKDIR /app
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
RUN python setup.py bdist_wheel
# Production stage
FROM python:3.9-slim-buster
WORKDIR /app
COPY --from=build /app/dist/*.whl ./
RUN pip install --no-cache-dir *.whl
EXPOSE 5000
CMD ["python", "-m", "myapp"]
Let's look at some pros and cons of using multistage images:
Pros:
Reduced image size: Multistage builds allow you to create smaller Docker images by removing unnecessary files and dependencies. This can result in faster deployment times and reduced storage costs.
Faster builds: Multistage builds can speed up the build process since the intermediate images are discarded, and only the final image is kept.
Improved security: Since the intermediate images are discarded, there are fewer attack surfaces, which can improve security.
Easier maintenance: Multistage builds can make it easier to maintain Docker images since they separate the build process from the runtime environment.
Simplified Dockerfile: Multistage builds can simplify Dockerfiles by separating the build instructions from the runtime instructions. This can make it easier to read and understand Dockerfiles.
Cons:
Complexity: Multistage builds can be more complex than single-stage builds, especially if the application has many dependencies.
Increased build time: Multistage builds can take longer to build, especially if the build process is complex.
Less flexibility: Multistage builds can be less flexible than single-stage builds since the intermediate images cannot be reused for other purposes.
Requires Docker 17.05 or higher: Multistage builds require Docker 17.05 or higher, which may not be available in some environments.