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-rw-r--r--nix-modules/.gitignore1
-rw-r--r--nix-modules/Readme.org57
-rw-r--r--nix-modules/docker-nixos-modules.nix90
-rw-r--r--nix-modules/example.nix22
4 files changed, 170 insertions, 0 deletions
diff --git a/nix-modules/.gitignore b/nix-modules/.gitignore
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+++ b/nix-modules/.gitignore
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+result
diff --git a/nix-modules/Readme.org b/nix-modules/Readme.org
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+#+TITLE: NixOS modules in OCI container
+
+* Idea
+Nix makes it easy to build small oci containers (docker/podman) using
+its package set, which will contain nothing that isn't absolutely
+necessary.
+
+However, this only applies to packages, not the NixOS module system
+that is usually used to generate config files from the Nix language,
+which are then wrapped into systemd module files. Unfortunately,
+systemd cannot run in docker (and would present a lot of unnecessary
+overhead).
+
+This is an experiment at redefining the NixOS module responsible for
+generating the systemd unit files to generate simple shell scripts
+that can serve as an entrypoint for the OCI containers instead that
+run the same services as they would on NixOS.
+
+* Running
+There's an example running a grafana server in ~example.nix~. Build
+it with:
+
+#+begin_src sh
+docker load < $(nix-build example.nix)
+#+end_src
+
+Then run the image name that docker prints out:
+
+#+begin_src sh
+docker run -p 3000:3000 -t grafana:ib6aahrmhqbzk444b8nq384zrg86fzdm
+#+end_src
+
+The full image is about 66MB, compared to 204MB for the official
+~grafana/grafana~ image.
+
+To use this with other modules than grafana, you will have to import
+them manually (and hope that these work). A list of all modules can be
+found in ~nixpkgs/nixos/modules/module-list.nix~.
+
+* Caveats
+Currently there is only support for:
+ - systemd.services
+ - users.users.<name>.home
+ - assertions
+
+Everything that cannot be reduced to just these will fail on build,
+and some of the things that do may still fail at runtime, since even
+the majority of these suboptions will be ignored / have different
+semantics than they usually do.
+
+* Still Todo:
+ - [ ] safe shutdown: currently, containers will have to be killed and
+ ignore ~docker stop~
+ - [ ] handle systemd tmpdirs
+ - [ ] make the images multi-layered: one layer for base packages, one
+ for config files (to avoid redefining the entire container for each
+ config change)
diff --git a/nix-modules/docker-nixos-modules.nix b/nix-modules/docker-nixos-modules.nix
new file mode 100644
index 0000000..47107a7
--- /dev/null
+++ b/nix-modules/docker-nixos-modules.nix
@@ -0,0 +1,90 @@
+{ nixpkgsPath ? <nixpkgs>
+, ociconfig
+, name
+, ...}:
+
+let
+ pkgs = import nixpkgsPath {};
+
+ dummyOption = with pkgs.lib; mkOption {
+ type = types.attrs;
+ default = {};
+ };
+
+ systemModule = { lib, config, ... }: {
+ options = {
+ toplevel = lib.mkOption {
+ type = lib.types.str;
+ };
+
+ systemd = with lib; {
+ services = dummyOption;
+ targets = dummyOption;
+ timers = dummyOption;
+ };
+
+ environment = dummyOption;
+ users.users = dummyOption;
+ users.groups = dummyOption;
+ meta = dummyOption;
+
+ networking.enableIPv6 = lib.mkOption {
+ type = lib.types.bool;
+ default = false;
+ };
+ };
+
+ config._module.args.pkgs = pkgs;
+ };
+
+ config = pkgs.lib.evalModules {
+ modules = [
+ systemModule
+ ociconfig
+ "${nixpkgsPath}/nixos/modules/misc/assertions.nix"
+ ];
+ };
+
+in pkgs.dockerTools.buildImage {
+ inherit name;
+
+ contents = pkgs.coreutils;
+
+ runAsRoot = (with pkgs.lib;
+ strings.concatStrings
+ (mapAttrsToList
+ (n: u: if u ? createHome && u.createHome then ("mkdir -p ${u.home}\n") else "")
+ config.config.users.users));
+
+ config = with pkgs.lib; {
+ Cmd = pkgs.writeShellScript "main-entrypoint"
+ (strings.concatStrings
+ (map (command: "${command}&")
+ (mapAttrsToList
+ (name: service:
+ (pkgs.writeShellScript
+ "systemd-script-${name}"
+ ''
+ #!${pkgs.dash.outPath}/bin/sh
+ set -ueo pipefail
+ ${if service ? preStart
+ then ''
+ echo ${escapeShellArg name}: running preStart script
+ ${service.preStart}
+ ''
+ else ""}
+ echo ${name}: starting ...
+ ${if service ? serviceConfig && service.serviceConfig ? WorkingDirectory
+ then "cd ${service.serviceConfig.WorkingDirectory}"
+ else ""}
+ ${if service ? environment
+ then (strings.concatStrings
+ (mapAttrsToList
+ (n: k: "export ${n}=${escapeShellArg k}\n")
+ service.environment))
+ + service.script
+ else ""}
+ '').outPath)
+ config.config.systemd.services)) + "\n wait");
+ };
+}
diff --git a/nix-modules/example.nix b/nix-modules/example.nix
new file mode 100644
index 0000000..2596df6
--- /dev/null
+++ b/nix-modules/example.nix
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+{pkgs ? import <nixpkgs> {}, ...}:
+
+import ./docker-nixos-modules.nix {
+ name = "grafana";
+ nixpkgsPath = <nixpkgs>;
+
+ ociconfig = {pkgs, config, ...}: {
+
+ imports = [
+ <nixpkgs/nixos/modules/services/monitoring/grafana.nix>
+ <nixpkgs/nixos/modules/services/web-servers/nginx/default.nix>
+ <nixpkgs/nixos/modules/security/acme.nix>
+ ];
+
+ services.grafana = {
+ enable = true;
+ dataDir = "/data";
+ addr = "0.0.0.0";
+ };
+
+ };
+}