Docker 1.5 Brings IPv6 Support to Containers

The first major milestone release from the open-source Docker project in 2015 debuts with new features that will pave the way for the year ahead.


The open-source Docker project rolled out its 1.5 release on Feb. 10, providing users of the application virtualization container technology with new networking and visibility capabilities.

Docker is an increasingly popular open-source technology that can enable application virtualization in containers. A number of large vendors, including IBM, Amazon, VMware, Microsoft and Red Hat, have embraced Docker over the course of the last year as a way to package and deploy virtualized applications. Docker 1.0 was released in June 2014, and the technology has been steadily evolving ever since.

In Docker 1.5, one of the major new features is support for next-generation IPv6 network addressing. IPv4 has been the default network addressing protocol in Docker since the project started, but the IPv4 space is dwindling. IPv4 has a 32-bit address space, compared with IPv6's much larger 128-bit address space.

"By default, the Docker server configures the container network for IPv4 only," the Docker 1.5 release notes explain. "You can enable IPv4/IPv6 dualstack support by running the Docker daemon with the --ipv6 flag."

In a dual-stack configuration, a Docker container will be accessible over both IPv4- and IPv6-enabled networks.

While IPv6 support was added to Docker 1.5 to expand accessibility, also added was a feature that restricts access for improved application data security and data resilience. With version 1.5, Docker now can label a container as read-only, which means the root filesystem in the container cannot be written to. That feature can have security implications as well as help to improve data persistence.

"This can be used in combination with volumes to force a container's process to only write to locations that will be persisted," the git pull request for the read-only feature states. "This is useful in many cases where the admin controls where they would like developers to write files and error on any other locations."

For any type of application workload, IT administrators typically want and need to have visibility to help improve operations and optimize configuration. While Docker users have had some limited visibility options in the past, with Docker 1.5, visibility is improved by way of the new Docker stats API. The Docker stats API provides data on application memory, CPU and network usage.

In addition to the Docker 1.5 release, the Docker community is pushing forward on a container image specification.

"An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime," the image spec document states. "This specification outlines the format of these filesystem changes and corresponding parameters and describes how to create and use them for use with a container runtime and execution tool."

Though version 1.5 is the first major milestone release in 2015, the Docker project itself has been busy laying the groundwork for the year ahead. On Jan. 28, the Docker project announced organizational updates, with the project's leadership divided into three core leadership roles: a chief architect, a chief maintainer and a chief operator.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.