helmfile-nix

A small wrapper around helmfile to allow writing your declarations in the nix language. This avoids any YAML or go templating, while still taking advantage of helmfile's features.

Basic usage

helmfile-nix render

Looks for helmfile.nix in the current directory and renders it to a helmfile.yaml to stdout.

helmfile-nix -f foo/helmfile.nix -e stage diff

Renders the helmfile in stage and passes it on to helmfile diff.

For convenience we default to 'dev' if env is not set.

• You can also check out this presentation given to the Oslo NixOS User Group for a quick overview.

Structure of your helmfile.nix

{ ... }: [
  { environments = { dev = { values = [ ]; }; }; }
  {
    repositories = [{
      name = "grafana";
      url = "https://grafana.github.io/helm-charts";
    }];
    releases = [{
      name = "grafana";
      chart = "grafana/grafana";
    }];
  }
]

Note that we expect an array of YAML documents, typically the first document is the environment configuration and any defaults. The follow optional attributes can be imported in your helmfile.nix:

Attribute	Description
lib	nixpkgs stdlib
var	This will contain your environment variables, as well as the environment name.
	Follows the same structure as helmfile (var.environment.name / var.values.foo).
escape_var	A function to escape a string for use in a helmfile template.

Options

helmfile-nix support all the helmfile options, in addition to:

Option	Description
--show-trace	Show a stack trace on error. This is passed to nix for the rendering and is
	meant to be used when you see an error during render. In most cases the
	error will point you to the right place though.
--state-value-set	helmfile-nix will use this to override values, but it is also
	passed on to helmfile. This is useful if you want to override a state value
	at runtime. For example, if you want to override the image of a pod temporarily.
-e env	The environment to use. Defaults to 'dev'.
-f file	The helmfile.nix to use. Defaults to looking in the current directory.

go templating in helmfile 1.0 and beyond

helmfile 1.0 disabled go templating by default, but you can enable it for helmfile-nix by naming your helmfile helmfile.gotmpl.nix. Having said that, in the wast majority of the cases nix has been enough to express the logic we've needed. Having it disabled also means you can directly have gotmpl syntax in your yaml file in cases where the helm charts use it, for example in alertmanager.

nix charts

helmfile-nix also allows you to write charts in nix, which can be useful for writing simple dynamic charts without needing to write yaml+go templating.

{ lib, var, escape_var }:
{
  name = "mychart";
  nixChart = "../mychart";
  namespace = "default";
  values = {
    foo = "bar";
    baz = escape_var "${var.environment.name}";
  } ;
}

The chart will be rendered to a temporary directory and passed to helmfile for processing, which will treat it as a static folder and use chartify to generate a chart. Look at testData/helm-nixchart for a trivial example.

Useful links

• helmfile - A declarative helm wrapper.
• noogle - A nix function search engine.
• nix.dev - The official nix documentation.

Caveats

• We expect a env structure with a env/ directory in the same directory as the helmfile.nix file containing a default.yaml and a $env.yaml file for each environment.
• Even though your helmfile gets further values, they can not be processed by nix.