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Using Docker and .NET together was brought up in the year 2017, where Microsoft explained the cons of using them together. Last year’s DockerCon update showed multiple .NET demos showing how one can use Docker for modern applications and for older applications that use traditional architectures. This eased users to containerize .NET applications using tools from both Microsoft and Docker. The team said that “most of their effort to improve the .NET Core Docker experience in the last year has been focused on .NET Core 3.0.”

“This is the first release in which we’ve made substantive runtime changes to make CoreCLR much more efficient, honor Docker resource limits better by default, and offer more configuration for you to tweak”. Microsoft writes in one of their blog posts. The team also mentions that they are invested in making .NET Core a true container runtime. They look forward to hardening .NET’s runtime to make it container-aware and function efficiently in low-memory environments.

Let’s have a look at the different advantages of bring Docker and .NET together

Docker + .NET advantages

Lesser memory allocation and fewer GC heaps by default

With .NET 3.0, the team reduced the minimal generation 0 GC allocation budget to better align with modern processor cache sizes and cache hierarchy. With this, the initial allocation size, which was unnecessarily large, was significantly reduced without any perceivable loss of performance thus bringing in tens of percentage points of improvements.

The team also mention about a new policy for determining how many GC heaps to create. This is most important on machines where a low memory limit is set, but no CPU limit is set on a machine with many CPU cores. The GC now reserves a memory segment with a minimum size of 16 MB per heap. This limits the number of heaps the GC will create.

Both these changes result in lower memory usage by default and make the default .NET Core configuration better in more cases.

Added PowerShell to .NET Core SDK container Images

PowerShell Core has been added to the .NET Core SDK Docker container images, per requests from the community. There are two main scenarios that having PowerShell inside the .NET Core SDK container image enables, which were not otherwise possible:

  • Write .NET Core application Dockerfiles with PowerShell syntax, for any OS.
  • Write .NET Core application/library build logic that can be easily containerized.

Note: PowerShell Core is now available as part of .NET Core 3.0 SDK container images. It is not part of the .NET Core 3.0 SDK.

.NET Core Images now available via Microsoft Container Registry

Microsoft teams are now publishing container images to the Microsoft Container Registry (MCR). There are two primary reasons for this change:

  • Syndicate Microsoft-provided container images to multiple registries, like Docker Hub and Red Hat.
  • Use Microsoft Azure as a global CDN for delivering Microsoft-provided container images.

Platform matrix and support

With .NET Core, we try to support a broad set of distros and versions. Following is the policy for each distro:

  • Alpine: support tip and retain support for one quarter (3 months) after a new version is released. Currently, 3.9 is tip and the team will stop producing 3.8 images in a month or two.
  • Debian: support one Debian version per latest .NET Core version. This is also the default Linux image used for a given multi-arch tag. For .NET Core 3.0, the team may publish Debian 10 based images. However, they may produce Debian 9 based images for .NET Core 2.1 and 2.2, and Debian 8 images for earlier .NET Core versions.
  • Ubuntu:  support one Ubuntu version per the latest .NET Core version(18.04). Also, as the team gets to know of a new Ubuntu LTS versions, they will start supporting non-LTS Ubuntu versions a means of validating the new LTS versions.

For Windows, they support the cross-product of Nano Server and .NET Core versions.

ARM Architecture

The team plans to add support for ARM64 on Linux with .NET Core 3.0, complementing the ARM32 and X64 support already in place. This will enable .NET Core to be used in even more environments.

Apart from these advantages, the team has also added support for Docker Memory and CPU Limits.

To know more about this partnership in detail, read Microsoft’s official blogpost.

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