What Is New in Docker Engine 1.6
Docker Engine 1.6 delivered significant updates across its core components, focusing on stability, image management, and platform support. This release tightened security for image tags and expanded compatibility with new hardware architectures.
| Category | Key Changes |
|---|---|
| New Features | Windows Client Preview, Official Raspberry Pi Support, Content Trust (Notary) for image signing |
| Improvements | Logging driver enhancements, docker stats improvements, docker events output |
| Bug Fixes | OverlayFS fixes, device mapper stability, network and volume operation corrections |
| Security | Mandatory image tag verification with Content Trust, TLS certificate validation |
| Deprecations | Legacy registry communication (index.docker.io), old command syntax |
How did image security change with Content Trust?
Docker 1.6 introduced Content Trust, a major security feature powered by the Notary project. This allows publishers to sign images and users to verify their authenticity before pulling them. In practice, this prevents man-in-the-middle attacks and ensures you're running the exact image a developer intended.
You can enable it by setting the DOCKER_CONTENT_TRUST environment variable to 1. Once active, commands like docker pull will fail if the image tag isn't signed, forcing a more secure workflow.
What new platforms did Docker Engine 1.6 support?
This release officially brought Docker to the Raspberry Pi, a huge win for IoT development. It also included a preview of the Docker Client for Windows, which was a first step towards the broader Windows container support that followed.
For developers, this meant you could finally run Docker natively on your ARM-based devices without custom builds. The Windows client preview was a clear signal of Docker's expansion beyond the Linux ecosystem.
Were there any logging improvements?
Yes, the logging subsystem got a nice boost. The json-file logging driver, which is the default, became more efficient at log rotation and managing disk space usage.
They also improved the handling of logging options for containers, making it easier to configure log rotation policies directly through daemon flags. This matters because it helps prevent containers from filling up disk space with logs in long-running deployments.
What fixes landed for storage drivers?
Several stability fixes were made for the OverlayFS and Device Mapper storage drivers. These are critical low-level components that manage how container images and writable layers are stored on disk.
The fixes addressed issues that could sometimes lead to corruption or performance problems, especially under heavy load. If you were running into weird filesystem errors on certain kernels, this release likely resolved them.
FAQ
How do I enable Content Trust to verify image signatures?
Set the environment variable DOCKER_CONTENT_TRUST=1 before running your Docker commands. Once enabled, the CLI will only pull images that have been signed with a valid key.
Is the Windows Client in 1.6 for running Windows containers?
No, the initial preview was a client-only release for connecting to a Docker Engine running on a Linux host. It was a CLI tool for Windows users, not a daemon for Windows containers.
Why was official Raspberry Pi support a big deal?
Before this, running Docker on ARM devices required manually compiling the engine or using community-built images. Official support meant guaranteed compatibility and easy installation via standard packages.
Did docker stats get any new features?
Yes, the output was improved to provide more consistent and reliable real-time statistics about container resource usage like CPU, memory, and network I/O.
What registry changes should I be aware of?
Docker 1.6 began the move away from the old registry API. It started using the new Docker Hub API by default, which is faster and more reliable.