Docker Engine 17.09: What's New, Release History & EOL Status

What Is New in Docker Engine 17.09

Docker 17.09 CE brought significant enhancements focused on the builder, runtime, and networking. This release merged the previously separate Docker CE and EE codebases into a single stream, simplifying the development process.

How did multi-stage builds change Dockerfile creation?

Multi-stage builds are the standout feature of 17.09, fundamentally changing how we write efficient Dockerfiles. They allow you to use multiple FROM statements in a single Dockerfile, each starting a new build stage.

You can copy artifacts from one stage to another, letting you separate your build-time dependencies from your final runtime image. In practice, this means you can have a stage with the entire compiler toolchain to build your application, and then copy just the resulting binary into a lean, production-ready stage based on a minimal base image like Alpine.

This slashes image size and reduces attack surface by eliminating build tools from the final image. The syntax is straightforward:

FROM golang:1.21 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp .

FROM alpine:latest
COPY --from=builder /app/myapp /
CMD ["/myapp"]

What networking improvements were introduced for Windows and Swarm?

17.09 expanded networking capabilities to better support Windows workloads and enhance Swarm service discovery. The MACvlan driver became available for Windows containers, giving them direct access to the physical network with their own MAC address.

For Swarm mode, a new internal DNS-based load balancer was added. It performs round-robin DNS resolution for service names, providing a simple and effective way to distribute network connections across all tasks of a service.

This is a lightweight alternative to the traditional routing mesh and is useful for scenarios where clients can handle DNS-based load balancing, like custom service discovery systems.

How did the builder get more powerful beyond multi-stage?

Beyond multi-stage builds, the builder gained several quality-of-life improvements. The COPY and ADD instructions now support a --chown flag to directly set file ownership, eliminating the need for a separate RUN chown command and the extra layer it created.

You could also specify a network mode for a build stage using the --network flag. This is crucial for controlling the network environment during the build process, which can affect how your application dependencies are fetched.

These changes made Dockerfiles more concise, efficient, and secure by reducing layer count and providing finer control over the build environment.

What was the significance of the unified CE/EE codebase?

This release marked the completion of the project to unify the codebases for Docker Community Edition (CE) and Enterprise Edition (EE). From 17.09 onward, both editions were built from the same underlying code.

For users, this meant that Docker CE became the upstream source for Docker EE. The community edition got even more stable and well-tested, as it was now the foundation for the enterprise product. This move simplified the entire release process and ensured feature parity.