containers-from-scratch

Build Your Own Container Using Less than 100 Lines of Go. This is a toy container build from scratch in Go solely for learning purpose. It uses namespaces and cgroups.

This will start our container (needs root privilege for creating cgroup):

sudo su
go run main.go run /bin/bash

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Sources of the inspiration and information

Building Containers from Scratch with Go by Liz Rice https://www.safaribooksonline.com/videos/building-containers-from/9781491988404

If you don't have access to safaribooksonline.com, Liz Rice gave talk on the same topic in several conferences too. One of them is "GOTO 2018 • Containers From Scratch": https://www.youtube.com/watch?v=8fi7uSYlOdc

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Further reading

Namespaces in Go

Part 1: Linux Namespaces https://medium.com/@teddyking/linux-namespaces-850489d3ccf

Part 2: Namespaces in Go - Basics https://medium.com/@teddyking/namespaces-in-go-basics-e3f0fc1ff69a

Part 3: Namespaces in Go - User https://medium.com/@teddyking/namespaces-in-go-user-a54ef9476f2a

Part 4: Namespaces in Go - reexec https://medium.com/@teddyking/namespaces-in-go-reexec-3d1295b91af8

Part 5: Namespaces in Go - Mount https://medium.com/@teddyking/namespaces-in-go-mount-e4c04fe9fb29

Part 6: Namespaces in Go - Network https://medium.com/@teddyking/namespaces-in-go-network-fdcf63e76100

Part 7: Namespaces in Go - UTS https://medium.com/@teddyking/namespaces-in-go-uts-d47aebcdf00e

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Bonus tip: Setting up VS Code for cross-platform development

I have used fedora to develop the container from scratch. However, if you are using a non-Linux OS (like macOS or Windows),the development experience is not great because a lot of pieces of this application is Linux specific. For example, calls like syscall.Sethostname or the Cloneflags field in the syscall.SysProcAttr{} struct is not available in intellisense in VSCode when the dev environment is not Linux. VS Code will mark those lines as errors, because they are platform specific and declared in the standard library in Go for Linux only.

Fortunately the workaround is very simple. Search for "go.toolsEnvVars" in VS Code settings, copy it to User Settings and change it to:

    "go.toolsEnvVars": {
        "GOOS": "linux"
    }

Restarting VS Code after that will recognize all Linux specific declarations and will not see them as errors. Go-to-definition will work properly too.

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