Docker has released version 1.5 of its container software, adding a number of new features as well as resolving several persistent problems.
Key new features include IPv6 support, a way to view resource-usage statistics, the addition of read-only containers, and the ability to specify which file to use in a build instead of the default Dockerfile.
Docker set out 1.5's main attributes in a blogpost, saying that in addition to the new features it has "smashed many long-standing, annoying bugs".
The appearance of the new -ipv6 flag allows users to allocate an IPv6 address to each container, enabling IPv6 networking between containers and on the special Linux docker0 bridge created on startup.
"You can resolve IPv6 addresses from within a container. You can even use this feature to have containers communicate across multiple hosts," Docker contributor Malte Janduda said in the company blogpost.
Docker 1.5 also enables a container to have a read-only file system, through the use of the --read-only flag.
"The read-only feature allows you to restrict the locations that an application inside a container can write files to. By using this capability in combination with volumes, you can make sure containers only persist data where it can be managed in a known location," Docker contributor Michael Crosby said.
With version 1.5, a new statistics command appears in Docker, docker stats CONTAINERID, which allows users to see a continuously updating stream of container resource usage statistics.
"In Docker 1.5, we introduce a new stats API endpoint and CLI command that will stream live CPU, memory, network IO and block IO for your containers. You can use the API endpoint to build tools that feed live resource information for your containers into your existing monitoring solutions, or build live dashboards directly using the API," Crosby said.
According to Docker contributor Doug Davis, being able to pick the file to use in a Docker build, rather than relying on the default Dockerfile, may be one of the most requested features of the past few months.
"[The command] docker build -f allows you to define multiple Dockerfiles in a single project and specify which one to use at build time. This can be helpful if you require separate Dockerfiles for testing and production environments," Davis said.
Among other features, Docker 1.5 also includes the v1 Open Image specification, so that the current Docker image format and metadata can be documented.
Docker said the 1.5 release offers a number of "significant performance improvements in build and image management".
By automating the creation and deployment of apps in containers - a lighter-weight form of virtualisation - Docker is designed to free developers from software and infrastructure dependencies, cutting costs and creating efficiencies in the process.
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