commit dc294b034e7908731ff01c903925c89e763303e1
Author: Robert Hensing <robert@roberthensing.nl>
Date:   Mon Dec 17 19:08:38 2018 +0100

    Code taken from Hercules CI repo
    
     - renamed to Arion
     - minor changes
     - readme WIP

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..43728b7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,48 @@
+
+# Run docker-compose without images with Nix
+
+*Wait, what?*
+
+With Arion you can fire up containers without creating images for each
+service. Instead, it uses a mostly empty image, sort of like a base
+image, and makes the host's Nix store available in the container,
+allowing the container to run programs without having to re-package
+them into a docker image.
+
+Arion is configured using Nix with modules, like those in
+NixOS. Similar to `docker-compose` it can therefore combine
+configuration from multiple files. For managing the network and
+containers it delegates to the `docker-compose` command.
+
+# Project Status
+
+This project was born out of a process supervision need for local
+development environments while working
+on [Hercules CI](https://www.hercules-ci.com). (It was also born out
+of ancient Greek deities disguised as horses. More on that later.)
+
+We don't use it to deploy to 'real' environments and we have no plans
+to do so in the future.
+
+If you do want to use Arion for 'real' environments, you'll probably
+want to either build images or manage garbage collection roots if you
+control the deployment host. Either of these has yet to be
+implemented.
+
+# How do I use Arion?
+
+The command line inherits most `docker-compose` commands. These
+examples assume you're in this repo's `examples/` directory.
+
+TODO examples
+
+# Why "Arion"?
+
+Arion comes from Greek mythology. Poseidon, the god of ~Docker~ the
+seas had his eye on Demeter. Demeter tried to trick him by disguising
+as a horse, but Poseidon saw through the deception and they had Arion.
+
+So Arion is a super fast divine horse; the result of some weird
+mixing. Also it talks.
+
+(And we feel morally obliged to name our stuff after Greek mythology)
diff --git a/default.nix b/default.nix
new file mode 100644
index 0000000..440e4b5
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,26 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  inherit (pkgs) lib stdenv;
+
+  arion = stdenv.mkDerivation {
+    name = "arion";
+    src = ./src;
+    unpackPhase = "";
+    buildPhase = "";
+    installPhase = ''
+      mkdir -p $out/bin $out/share/arion
+      cp -a nix $out/share/arion/
+      cp -a arion-image $out/share/arion/
+      substitute arion $out/bin/arion \
+        --subst-var-by path ${lib.makeBinPath [pkgs.jq pkgs.coreutils]} \
+        --subst-var-by nix_dir $out/share/arion/nix \
+        ;
+      chmod a+x $out/bin/arion
+    '';
+  };
+
+in
+{
+  inherit arion;
+}
diff --git a/src/arion b/src/arion
new file mode 100755
index 0000000..f7f85f8
--- /dev/null
+++ b/src/arion
@@ -0,0 +1,199 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+export PATH="$PATH:@path@"
+
+nix_dir="@nix_dir@"
+docker_compose_args=()
+files=()
+command="docker-compose"
+pkgs_argument="./arion-pkgs.nix"
+
+debug() {
+    # echo "$@"
+    :
+}
+
+while test $# != 0; do
+    case "$1" in
+        -f|--file)
+            shift
+            files+=("$1")
+            ;;
+        -f*)
+            files+=("${1/#-f/}")
+            ;;
+        --file=*)
+            files+=("${1/#--file=}")
+            ;;
+        --pkgs)
+            shift
+            pkgs_argument="$1"
+            ;;
+        -h|--help|help)
+            command="help"
+            shift
+            break
+            ;;
+        cat)
+            command="$1"
+            shift
+            break
+            ;;
+        repl)
+            command="$1"
+            shift
+            break
+            ;;
+        docker-compose)
+            command="docker-compose"
+            shift
+            break
+            ;;
+        *)
+            break
+            ;;
+    esac
+    shift
+done
+
+while test $# != 0; do
+    docker_compose_args+=("$1")
+    shift
+done
+
+case "$command" in
+    help)
+        cat <<EOF
+
+Arion wraps your system's docker-compose, providing a NixOps-like
+experience for simple container deployments.
+
+Usage:
+  arion up|logs|...     - execute docker-compose commands
+  arion cat             - display raw docker-compose.yaml
+  arion config          - validate and display the config file
+  arion repl            - explore the config interactively
+  arion help
+  arion docker-compose help
+  arion docker-compose help up|logs|...
+
+EOF
+        exit 0
+        ;;
+    *)
+        ;;
+esac
+
+if [[ ${#files[@]} == 0 ]]; then
+    files=("./arion-compose.nix")
+fi
+
+
+debug docker_compose_args: "${docker_compose_args[@]}"
+debug files: "${files[@]}"
+
+docker_compose_yaml=.tmp-nix-docker-compose-$$-$RANDOM.yaml
+cleanup() {
+  rm -f $docker_compose_yaml
+}
+trap cleanup EXIT
+
+modules="["
+
+for file in "${files[@]}"; do
+    case "$file" in
+        /*)
+            modules="$modules (/. + $(printf '"%q"' $file))"
+            ;;
+        *)
+            modules="$modules (./. + $(printf '"/%q"' $file))"
+            ;;
+    esac
+done
+
+modules="$modules ]"
+
+debug modules: $modules
+
+old_IFS="$IFS"
+IFS=""
+args=(
+     )
+IFS="$old_IFS"
+for arg in "${args[@]}"; do
+    echo arg: $arg
+done
+
+do_build() {
+  echo 1>&2 "Building configuration..."
+  nix-build \
+    "$nix_dir/eval-docker-compose.nix" \
+    --out-link $docker_compose_yaml \
+    --argstr uid "$UID" \
+    --arg modules "$modules" \
+    --arg pkgs "$pkgs_argument" \
+    --show-trace \
+    --attr 'config.build.dockerComposeYaml' \
+    >/dev/null ;
+}
+
+
+do_repl() {
+    # nix repl doesn't autocall its <FILES> arguments
+    # so we improvise. We need a file in this directory
+    # to make sure that all paths are as expected :(
+    trap do_repl_cleanup EXIT;
+
+    REPL_TMP=.tmp-repl-$$-$RANDOM
+    cat <<EOF
+Launch a repl for you, using a temporary file: $REPL_TMP.
+
+This loads the configuration from the modules
+  $files
+
+To get started:
+
+To see deployment-wide configuration
+  type config. and hit TAB
+To see the services
+  type config.docker-compose.services TAB or ENTER
+To bring the top-level Nixpkgs attributes into scope
+  type :a (config._module.args.pkgs) // { inherit config; }
+
+EOF
+    cat >"$REPL_TMP" <<EOF
+import $nix_dir/eval-docker-compose.nix {
+  uid = "$UID";
+  modules = $modules;
+  pkgs = $pkgs_argument;
+}
+EOF
+
+    nix repl \
+        "$REPL_TMP" \
+        ;
+}
+do_repl_cleanup() {
+    rm -f $REPL_TMP
+}
+
+case "$command" in
+    cat)
+        do_build
+        cat $docker_compose_yaml | jq .
+        ;;
+    repl)
+        do_repl
+        ;;
+    docker-compose)
+        if [[ ${#docker_compose_args[@]} != 0
+           && ${docker_compose_args[0]} != "help"
+           && ${docker_compose_args[0]} != "version"
+           ]]; then
+            do_build
+        fi
+        docker-compose -f $docker_compose_yaml "${docker_compose_args[@]}"
+        ;;
+esac
diff --git a/src/arion-image/Dockerfile b/src/arion-image/Dockerfile
new file mode 100644
index 0000000..8c4159e
--- /dev/null
+++ b/src/arion-image/Dockerfile
@@ -0,0 +1,2 @@
+FROM scratch
+COPY passwd /etc/passwd
diff --git a/src/arion-image/passwd b/src/arion-image/passwd
new file mode 100644
index 0000000..321840c
--- /dev/null
+++ b/src/arion-image/passwd
@@ -0,0 +1,2 @@
+root:x:0:0:System administrator:/root:/bin/sh
+nobody:x:65534:65534:Unprivileged account (don't use!):/var/empty:/run/current-system/sw/bin/nologin
diff --git a/src/nix/docker-compose-module.nix b/src/nix/docker-compose-module.nix
new file mode 100644
index 0000000..1170a86
--- /dev/null
+++ b/src/nix/docker-compose-module.nix
@@ -0,0 +1,49 @@
+{ pkgs, uid, lib, config, ... }:
+
+let
+  evalService = name: modules:
+    let
+      composite = lib.evalModules {
+        check = true;
+        modules = builtinModules ++ modules;
+      };
+
+      builtinModules = [
+        argsModule
+        ./service.nix
+        ./service-host-store.nix
+      ];
+
+      argsModule = {
+        _file = ./docker-compose-module.nix;
+        key = ./docker-compose-module.nix;
+        config._module.args.pkgs = lib.mkForce pkgs;
+        config._module.args.uid = uid;
+      };
+
+    in
+      composite.config.build.service;
+
+in
+{
+  options = {
+    build.dockerComposeYaml = lib.mkOption {
+      type = lib.types.package;
+    };
+    docker-compose.raw = lib.mkOption {
+      type = lib.types.attrs;
+    };
+    docker-compose.services = lib.mkOption {
+      default = {};
+      type = with lib.types; attrsOf (coercedTo unspecified (a: [a]) (listOf unspecified));
+    };
+  };
+  config = {
+    build.dockerComposeYaml = pkgs.writeText "docker-compose.yaml" (builtins.toJSON (config.docker-compose.raw));
+
+    docker-compose.raw = {
+      version = "3";
+      services = lib.mapAttrs evalService config.docker-compose.services;
+    };
+  };
+}
diff --git a/src/nix/eval-docker-compose.nix b/src/nix/eval-docker-compose.nix
new file mode 100644
index 0000000..3eda5f1
--- /dev/null
+++ b/src/nix/eval-docker-compose.nix
@@ -0,0 +1,33 @@
+{ modules ? [], uid ? 0, pkgs }:
+
+let _pkgs = pkgs;
+in
+let
+  pkgs = if builtins.typeOf _pkgs == "path"
+         then import _pkgs
+         else if builtins.typeOf _pkgs == "set"
+         then _pkgs
+         else builtins.abort "The pkgs argument must be an attribute set or a path to an attribute set.";
+
+  inherit (pkgs) lib;
+
+  composite = lib.evalModules {
+    check = true;
+    modules = builtinModules ++ modules;
+  };
+
+  builtinModules = [
+    argsModule
+    ./docker-compose-module.nix
+  ];
+
+  argsModule = {
+    _file = ./eval-docker-compose.nix;
+    key = ./eval-docker-compose.nix;
+    config._module.args.pkgs = lib.mkIf (pkgs != null) (lib.mkForce pkgs);
+    config._module.args.uid = uid;
+  };
+
+in
+  # Typically you need composite.config.build.dockerComposeYaml
+  composite
diff --git a/src/nix/service-host-store.nix b/src/nix/service-host-store.nix
new file mode 100644
index 0000000..1bcd790
--- /dev/null
+++ b/src/nix/service-host-store.nix
@@ -0,0 +1,23 @@
+# Bind-mounts the host store
+{ lib, config, ... }:
+let
+  inherit (lib) mkOption types mkIf;
+in
+{
+  options = {
+    service.useHostStore = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Bind mounts the host store if enabled, avoiding copying.";
+    };
+  };
+  config = mkIf config.service.useHostStore {
+    service.image = "arion-base";
+    service.build.context = "${../arion-image}";
+    service.volumes = [
+      "/nix/store:/nix/store"
+      "/bin/sh:/bin/sh"
+      "/usr/bin/env:/usr/bin/env"
+    ];
+  };
+}
diff --git a/src/nix/service.nix b/src/nix/service.nix
new file mode 100644
index 0000000..2e06e48
--- /dev/null
+++ b/src/nix/service.nix
@@ -0,0 +1,74 @@
+{ pkgs, lib, config, ... }:
+
+let
+  inherit (lib) mkOption types;
+  inherit (types) listOf nullOr attrsOf string either;
+
+in
+{
+  options = {
+    service.volumes = mkOption {
+      type = listOf types.unspecified;
+      default = [];
+    };
+    service.build.context = mkOption {
+      type = nullOr string;
+      default = null;
+    };
+    service.environment = mkOption {
+      type = attrsOf string;
+      default = {};
+    };
+    service.image = mkOption {
+      type = string;
+    };
+    service.command = mkOption {
+      type = nullOr types.unspecified;
+      default = null;
+    };
+    service.depends_on = mkOption {
+      type = listOf string;
+      default = [];
+    };
+    service.restart = mkOption {
+      type = nullOr string;
+      default = null;
+    };
+    service.ports = mkOption {
+      type = listOf types.unspecified;
+      default = [];
+      description = ''
+        Expose ports on host. "host:container" or structured.
+        See https://docs.docker.com/compose/compose-file/#ports
+      '';
+    };
+    service.expose = mkOption {
+      type = listOf string;
+      default = [];
+    };
+
+    build.service = mkOption {
+      type = attrsOf types.unspecified;
+    };
+  };
+
+  config.build.service = {
+    inherit (config.service)
+      volumes
+      environment
+      image
+      ;
+  } // lib.optionalAttrs (config.service.build.context != null) {
+    inherit (config.service) build;
+  } // lib.optionalAttrs (config.service.command != null) {
+    inherit (config.service) command;
+  } // lib.optionalAttrs (config.service.depends_on != []) {
+    inherit (config.service) depends_on;
+  } // lib.optionalAttrs (config.service.restart != null) {
+    inherit (config.service) restart;
+  } // lib.optionalAttrs (config.service.ports != []) {
+    inherit (config.service) ports;
+  } // lib.optionalAttrs (config.service.expose != []) {
+    inherit (config.service) expose;
+  };
+}