Nim Containertools:

My HackWeek-22 project

Project scope and purpose

• Practice with Nim's advanced features: macros and metaprogramming
• Play with container technology
• Develop a POC that can be expanded for future cases
• Use Test Driven Development methodology to design and develop code
• Have fun and try out something different
• Publish something on official nimble package directory: https://nimble.directory/pkg/containertools

What's the Nim programming language ?

Efficient, expressive, elegant

Nim is a statically typed compiled systems programming language.

• Intuitive and clean syntax, inspired from Python, Ada and Modula.
• Support for multiple operating systems
• Compiles to native binary or Javascript
• Easy C, C++ and objC wrapping
• Decentralised package management
• trivia: openSUSE has "first-class support" for the Nim language (phoronix)

Feel free to join #discuss-nim slack channel

A plain, old Containerfile

Containerfile is a plain text file with a simple syntax, composed of instructions that specifies how to create a container image.

   FROM nginx
   COPY index.html /usr/share/nginx/html
   EXPOSE 8O8O
   CMD ["nginx", "-g", "daemon off;"]

While effective, it has some issues:

• no syntax checking until build/runtime (which usually happens in a CI)
• only static values, cannot have any logic or variable

Hello, ContainerTools

Containerfile declarative syntax is static and can be error prone. The library provides a DSL (Domain Specific Language) that enables a dynamic behaviour, while the strict checking of the Nim compiler ensure correctness.

import containertools
let image = container:
    FROM "opensuse/leap"
    CMD "echo Hello"

image.save "Containerfile"
image.build  

Static typechecking safety ...

import containertools
let image = container:
   FROM nginx
   COPY index.html /usr/share/nginx/html
   EXPOSE 8O8O
   CMD ["nginx", "-g", "daemon off;"]
image.save "Containerfile"
image.build  

oops, we did an error. Can you spot it ?

... ensured by the compiler / IDE tooling

$ nim compile
error.nim(5, 11) Error: invalid token. Expected a numeric value

Easiness of declarative syntax ...

import std/[strformat, times]
import containertools

for distro in ["leap","tumbleweed"]:
    let image = container:
        FROM "opensuse/" & distro
        if distro=="tumbleweed": # this a is Nim statement
          RUN "zypper -n install mypkg"
        CMD &"echo Hello from {distro} container built on {now()}"
    image.save "Containerfile." & distro
    image.build

... with the power of a programming language

we can also import an "existing" Containerfile and check it for errors, suggest optimizations and fix security issues

How can it be useful for you @ SUSE ?

Writing declarative files (YAML?) is getting more and more common (Dockerfiles,K8S definitions, CI actions, openQA schedules)

• As the size grows, they get tedious to maintain and error-prone
• Having the support of a strong typed compiler and tooling helps to increase flexibility, modularity and reduce human errors
• The library can also work as a linter: import/parse an existing declarative definition (provided from customer ?) and give hints about possible optimizations or security issues

Whole project was developed using TDD

1. Think of a feature
2. Write a failing test
3. Write just enough code to pass the test
4. Refactor when needed
5. Goto step 1

Lessons taken

• Having a good testsuite gives you freedom to a fearless refactor. During the design phase I used the growing test suite as a platform to try out new ideas
• TDD lets you think from the user's perspective
• Metaprogramming can be hard but is very powerful and expressive
• Good code is important, but examples and documentation are fundamental
• Choice of OSS license is also important

Thank you!

Questions ?

These slides are available at https://github.com/ilmanzo/suse_presentations/