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docs(ops/terraform/deploy-nixos): document inputs and outputs

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This documents the input and output format, and also removes some
references to Terraform and evaluating NixOS system configurations.

It can be used to evaluate anything.

Change-Id: I8492cc3e386f89b299469c78e586644ee82a708f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11213
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
This commit is contained in:
Florian Klink 2024-03-20 15:19:37 +02:00 committed by clbot
parent 798f8b9d43
commit 3281fb9132
3 changed files with 35 additions and 22 deletions
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2
ops/terraform/deploy-nixos/main.tf
View file

@ -53,7 +53,7 @@ variable "triggers" {
# Fetch the derivation hash for the NixOS system.
data "external" "nixos_system" {
program = ["${path.module}/nixos-eval.sh"]
program = ["${path.module}/nix-eval.sh"]
query = {
attrpath = var.attrpath

34
ops/terraform/deploy-nixos/nix-eval.sh Executable file
View file

@ -0,0 +1,34 @@
#!/usr/bin/env bash
# SPDX-FileCopyrightText: 2023 The TVL Authors
#
# SPDX-License-Identifier: MIT
set -ueo pipefail
# Evaluates a Nix expression.
#
# Receives input parameters as JSON from stdin.
# It expects a dict with the following keys:
#
# - `attrpath`: the attribute.path pointing to the expression to instantiate.
# Required.
# - `entrypoint`: the path to the Nix file to invoke.
# Optional. If omitted, will shell out to git to determine the repo root,
# and Nix will use `default.nix` in there.
# - `argstr`: A map containing string keys and values
# which are passed to Nix as `--argstr $key $value`
# command line args. Optional.
#
# jq's @sh format takes care of escaping.
eval "$(jq -r '@sh "attrpath=\(.attrpath) && entrypoint=\(.entrypoint) && argstr=\((.argstr // {}) | to_entries | map ("--argstr", .key, .value) | join(" "))"')"
# Evaluate the expression.
[[ -z "$entrypoint" ]] && entrypoint=$(git rev-parse --show-toplevel)
# shellcheck disable=SC2086,SC2154
drv=$(nix-instantiate -A "${attrpath}" "${entrypoint}" ${argstr})
# Return a JSON back to stdout.
# It contains the following keys:
#
# - `drv`: the store path of the Derivation that has been instantiated.
jq -n --arg drv "$drv" '{"drv":$drv}'

21
ops/terraform/deploy-nixos/nixos-eval.sh
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@ -1,21 +0,0 @@
#!/usr/bin/env bash
# SPDX-FileCopyrightText: 2023 The TVL Authors
#
# SPDX-License-Identifier: MIT
#
# Builds a NixOS system configuration at the given attribute path.
set -ueo pipefail
# Load input variables from Terraform. jq's @sh format takes care of
# escaping.
eval "$(jq -r '@sh "attrpath=\(.attrpath) && entrypoint=\(.entrypoint) && argstr=\((.argstr // {}) | to_entries | map ("--argstr", .key, .value) | join(" "))"')"
# Evaluate the system derivation.
[[ -z "$entrypoint" ]] && entrypoint=$(git rev-parse --show-toplevel)
# shellcheck disable=SC2086,SC2154
system_drv=$(nix-instantiate -A "${attrpath}" "${entrypoint}" ${argstr})
# Return system derivation back to Terraform.
jq -n --arg drv "$system_drv" '{"drv":$drv}'