minimalish docker image

ChangeLog.md

@@ -14,6 +14,7 @@ This project's release branch is `master`. This log is written from the perspect
 * Use `--keep NIX_PATH` for all pure shells so references to `<nixpkgs>` continues to work.
 * Backport ACMEv2 support in obelisk server to regain LetsEncrypt account creation.
 * Enable https in `ob run`
+* Add Docker support, for building minimal and customizable images
 
 ## v0.2.0.0 - 2019-8-17
 

README.md

@@ -345,3 +345,61 @@ This should copy over and install the application on your device (if you see a
 ##### Build a release version
 
 After having configured signing for your app, you may proceed to build a release version of the app. This is no different to how you build the non-release version, so consult the section [Android](#android) further above for exact instructions on building and deploying to your device.
+
+
+## Docker
+
+### Variables
+
+Setting the following environment variables will be helpful for keeping build and run parameters consistent:
+
+```bash
+export NAME=app
+export VERSION=$(git rev-parse HEAD)
+export CONFIGDIR=/path/to/obelisk/config
+```
+
+### Building
+
+#### Default
+
+To build a Docker image using a default configuration, run:
+```
+docker load < $(nix-build -A dockerImage --no-out-link --argstr name $NAME --argstr version $VERSION)
+```
+
+#### Custom
+
+To build with a custom configuration, Obelisk's default configuration can be imported and overriden in a `release.nix` file added to your top-level directory:
+
+```nix 
+{ }:
+let
+  project = import ./. {};
+  obelisk = import ./.obelisk/impl {
+    system = builtins.currentSystem;
+  };
+  mkBaseDockerImageConfig = { version }: obelisk.dockerImageConfig { 
+    name = "app";
+    exe = project.linuxExe;
+    version = version;
+  };
+in { 
+  customDockerImage = args@{ version ? "latest" }: 
+    obelisk.nixpkgs.dockerTools.buildImage (mkBaseDockerImageConfig args // { 
+      config.expose = 3000; # overriding default port 8000
+    });
+}
+```
+
+The custom image can then be built with: `nix-build release.nix -A customDockerImage --no-out-link --argstr version $VERSION`
+
+### Running 
+
+Using the default configuration, the image can then be run with:
+
+```bash
+docker run -p 127.0.0.1:8000:8000/tcp --volume "$CONFIGDIR:/var/run/backend/config" "${NAME}:${VERSION}"
+```
+
+And the application should be accessible at `http://localhost:8000`.

default.nix

@@ -224,6 +224,35 @@ in rec {
     };
   };
 
+  dockerImageConfig = args@{exe, name, version, extraContents ? [], extraPaths ? []}: 
+    let
+      appDirSetupScript = nixpkgs.runCommand "appDirSetupScript.sh" {} ''
+        mkdir -p    $out/var/lib/backend
+        ln -sft $out/var/lib/backend '${exe}'/*
+        ${nixpkgs.findutils}/bin/find $out/var/lib/backend
+        '';
+    in {
+      name = name;
+      tag = version;
+      contents = [ nixpkgs.iana-etc nixpkgs.cacert appDirSetupScript ] ++ extraContents;
+      keepContentsDirlinks = true;
+      config = {
+        Env = [
+          ("PATH=" + builtins.concatStringsSep(":")(extraPaths ++ [
+            "/var/lib/backend" # put the obelisk project on the path.
+            "/bin" # put contents on path
+          ] ++ map (pkg: "${pkg}/bin") pkgs.stdenv.initialPath # put common tools in path so docker exec is useful
+          ))
+        ];
+        Expose = 8000;
+        Entrypoint = ["/var/lib/backend/backend"];
+        WorkingDir = "/var/lib/backend";
+        User = "99:99";
+      };
+    };
+
+  dockerImage = args: nixpkgs.dockerTools.buildImage (dockerImageConfig args);
+
   serverExe = backend: frontend: assets: optimizationLevel: version:
     pkgs.runCommand "serverExe" {} ''
       mkdir $out
@@ -349,6 +378,8 @@ in rec {
       exe = serverOn system dummyVersion;
       server = args@{ hostName, adminEmail, routeHost, enableHttps, version }:
         server (args // { exe = linuxExe version; });
+      dockerImage = args@{ name, version }:
+        dockerImage (args // { exe = linuxExe version; });
       obelisk = import (base + "/.obelisk/impl") {};
     };
   haskellPackageSets = {