diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 36fe7ffb..bdf23f22 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -35,7 +35,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install protobuf-compiler
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
@@ -43,7 +43,7 @@ jobs:
           profile: minimal
           toolchain: "1.65.0"
           override: true
-      - uses: Swatinem/rust-cache@6720f05bc48b77f96918929a9019fb2203ff71f8 # tag=v2.0.0
+      - uses: Swatinem/rust-cache@359a70e43a0bb8a13953b04a90f76428b4959bb6 # v2.2.0
         with:
           key: udeps
       - uses: actions-rs/cargo@844f36862e911db73fe0815f00a4a2602c279505 # renovate: tag=v1.0.3
@@ -111,10 +111,10 @@ jobs:
     continue-on-error: ${{ matrix.checks == 'advisories' }}
 
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
-      - uses: EmbarkStudios/cargo-deny-action@7257a18a9c2fe3f92b85d41ae473520dff953c97 # tag=v1.3.2
+      - uses: EmbarkStudios/cargo-deny-action@8a8607bd8e2b3a514d5a40174cc7c55b229d9ba7 # v1.4.0
         with:
           command: check ${{ matrix.checks }}
 
@@ -122,7 +122,7 @@ jobs:
     name: Run Rustfmt
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
@@ -144,7 +144,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install protobuf-compiler
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
@@ -153,7 +153,7 @@ jobs:
           toolchain: "1.65.0"
           components: clippy
           override: true
-      - uses: Swatinem/rust-cache@6720f05bc48b77f96918929a9019fb2203ff71f8 # tag=v2.0.0
+      - uses: Swatinem/rust-cache@359a70e43a0bb8a13953b04a90f76428b4959bb6 # v2.2.0
         with:
           key: clippy
       - name: Run clippy action to produce annotations
@@ -178,7 +178,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install protobuf-compiler
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
@@ -187,7 +187,7 @@ jobs:
           toolchain: "1.65.0"
           components: rustfmt
           override: true
-      - uses: Swatinem/rust-cache@6720f05bc48b77f96918929a9019fb2203ff71f8 # tag=v2.0.0
+      - uses: Swatinem/rust-cache@359a70e43a0bb8a13953b04a90f76428b4959bb6 # v2.2.0
         with:
           key: doc
       - uses: actions-rs/cargo@844f36862e911db73fe0815f00a4a2602c279505 # renovate: tag=v1.0.3
@@ -203,7 +203,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install protobuf-compiler
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
@@ -211,7 +211,7 @@ jobs:
           profile: minimal
           toolchain: "1.65.0"
           override: true
-      - uses: Swatinem/rust-cache@6720f05bc48b77f96918929a9019fb2203ff71f8 # tag=v2.0.0
+      - uses: Swatinem/rust-cache@359a70e43a0bb8a13953b04a90f76428b4959bb6 # v2.2.0
         with:
           key: test
       - uses: actions-rs/cargo@844f36862e911db73fe0815f00a4a2602c279505 # renovate: tag=v1.0.3
@@ -226,10 +226,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+        uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
-      - uses: actions/setup-python@v4
+      - uses: actions/setup-python@d27e3f3d7c64b4bbf8e4abfb9b63b83e846e0435 # v4
         with:
           python-version: '3.10'
       - name: Install jinja2-cli
@@ -240,7 +240,7 @@ jobs:
         run: git diff --exit-code
       - name: Git Diff showed uncommitted changes
         if: ${{ failure() }}
-        uses: actions/github-script@d50f485531ba88479582bc2da03ff424389af5c1 # tag=v6
+        uses: actions/github-script@d556feaca394842dc55e4734bf3bb9f685482fa0 # v6
         with:
           script: |
             core.setFailed('Committed README are not up to date, please make sure to apply them to the templated partials, and re-commit!')
@@ -264,11 +264,11 @@ jobs:
           sudo apt-get update
           sudo apt-get install protobuf-compiler
       - name: Checkout
-        uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+        uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
       - name: Set up Helm
-        uses: azure/setup-helm@b5b231a831f96336bbfeccc1329990f0005c5bb1 # tag=v3.3
+        uses: azure/setup-helm@5119fcb9089d432beecbf79bb2c7915207344b78 # v3.5
         with:
           version: v3.6.2
       - name: Set up cargo
@@ -278,7 +278,7 @@ jobs:
           toolchain: "1.65.0"
           override: true
       - name: Set up rust-cache
-        uses: Swatinem/rust-cache@6720f05bc48b77f96918929a9019fb2203ff71f8 # tag=v2.0.0
+        uses: Swatinem/rust-cache@359a70e43a0bb8a13953b04a90f76428b4959bb6 # v2.2.0
         with:
           key: charts
       - name: Regenerate charts
@@ -287,7 +287,7 @@ jobs:
         run: git diff --exit-code
       - name: Git Diff showed uncommitted changes
         if: ${{ failure() }}
-        uses: actions/github-script@7dff1a87643417cf3b95bb10b29f4c4bc60d8ebd # tag=v6
+        uses: actions/github-script@d556feaca394842dc55e4734bf3bb9f685482fa0 # v6
         with:
           script: |
             core.setFailed('Committed charts were not up to date, please regenerate and re-commit!')
@@ -324,10 +324,10 @@ jobs:
           sudo apt-get update
           sudo apt-get install protobuf-compiler
       - name: Checkout
-        uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+        uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
         with:
           submodules: recursive
-      - uses: actions/setup-python@b55428b1882923874294fa556849718a1d7f2ca5 # tag=v4
+      - uses: actions/setup-python@d27e3f3d7c64b4bbf8e4abfb9b63b83e846e0435 # v4
         if: ${{ github.event_name == 'pull_request' }}
       - uses: actions-rs/toolchain@16499b5e05bf2e26879000db0c1d13f7e13fa3af # renovate: tag=v1.0.7
         with:
diff --git a/.github/workflows/daily_security.yml b/.github/workflows/daily_security.yml
index b609d366..06b5d462 100644
--- a/.github/workflows/daily_security.yml
+++ b/.github/workflows/daily_security.yml
@@ -14,7 +14,7 @@ jobs:
   audit:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
       - uses: actions-rs/audit-check@35b7b53b1e25b55642157ac01b4adceb5b9ebef3 # renovate: tag=v1.2.0
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.github/workflows/reviewdog.yaml b/.github/workflows/reviewdog.yaml
index c91d5eac..fbc81952 100644
--- a/.github/workflows/reviewdog.yaml
+++ b/.github/workflows/reviewdog.yaml
@@ -13,16 +13,16 @@ jobs:
   actionlint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
-      - uses: reviewdog/action-actionlint@fe5c2db6029881e0b5634d7cb0d119b0c16b6922 # tag=v1.32.0
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+      - uses: reviewdog/action-actionlint@b6feb003955cad286985c42e7047f4567a798f3f # v1.36.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
 
   flake8:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
-      - uses: actions/setup-python@b55428b1882923874294fa556849718a1d7f2ca5 # tag=v4
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+      - uses: actions/setup-python@d27e3f3d7c64b4bbf8e4abfb9b63b83e846e0435 # v4
         with:
           python-version: "3.9"
       - uses: reviewdog/action-flake8@b6435e67f0cfda225b9e0c9283cfb7ea7c551bdb # tag=v3.6.0
@@ -32,15 +32,15 @@ jobs:
   hadolint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
-      - uses: reviewdog/action-hadolint@55be5d2c4b0b80d439247b128a9ded3747f92a29 # tag=v1.33.0
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+      - uses: reviewdog/action-hadolint@141ffd8d2f0b75e6fc7c87341331985448b62aa4 # v1.34.1
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
 
   markdownlint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
       - uses: reviewdog/action-markdownlint@97e3df02fe1573d505a7b268046a44fa5409cbc3 # tag=v0.9.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
@@ -49,15 +49,15 @@ jobs:
   shellcheck:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
-      - uses: reviewdog/action-shellcheck@66c9a47bf02255b250284a82251cb4cadf5043f5 # tag=v1.15.0
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
+      - uses: reviewdog/action-shellcheck@f52d78284b4941028952125a10c76676c3d456eb # v1.17.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
 
   yamllint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
       - uses: reviewdog/action-yamllint@8c429dfe4fc47b1ce1fa99a64e94693880d5dc30 # tag=v1.6.1
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.gitignore b/.gitignore
index 132b42c3..44b2140f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,4 +12,6 @@ target/
 Cargo.nix
 crate-hashes.json
 result
-image.tar
\ No newline at end of file
+image.tar
+
+tilt_options.json
\ No newline at end of file
diff --git a/Makefile b/Makefile
index b6a03c81..f2645f94 100644
--- a/Makefile
+++ b/Makefile
@@ -73,3 +73,6 @@ regenerate-charts: chart-clean compile-chart
 build: regenerate-charts helm-package docker-build
 
 publish: build docker-publish helm-publish
+
+run-dev:
+	nix run -f. tilt -- up --port 5441
\ No newline at end of file
diff --git a/Tiltfile b/Tiltfile
new file mode 100644
index 00000000..375a77e9
--- /dev/null
+++ b/Tiltfile
@@ -0,0 +1,36 @@
+# If tilt_options.json exists read it and load the default_registry value from it
+settings = read_json('tilt_options.json', default={})
+registry = settings.get('default_registry', 'docker.stackable.tech/sandbox')
+
+# Configure default registry either read from config file above, or with default value of "docker.stackable.tech/sandbox"
+default_registry(registry)
+
+meta = read_json('nix/meta.json')
+operator_name = meta['operator']['name']
+
+custom_build(
+    registry + '/' + operator_name,
+    'nix shell -f . crate2nix -c crate2nix generate && nix-build . -A docker --argstr dockerName "${EXPECTED_REGISTRY}/' + operator_name + '" && ./result/load-image | docker load',
+    deps=['rust', 'Cargo.toml', 'Cargo.lock', 'default.nix', "nix", 'build.rs', 'vendor'],
+    # ignore=['result*', 'Cargo.nix', 'target', *.yaml],
+    outputs_image_ref_to='result/ref',
+)
+
+# Load the latest CRDs from Nix
+watch_file('result')
+if os.path.exists('result'):
+   k8s_yaml('result/crds.yaml')
+
+# Exclude stale CRDs from Helm chart, and apply the rest
+helm_crds, helm_non_crds = filter_yaml(
+   helm(
+      'deploy/helm/' + operator_name,
+      name=operator_name,
+      set=[
+         'image.repository=' + registry + '/' + operator_name,
+      ],
+   ),
+   api_version = "^apiextensions\\.k8s\\.io/.*$",
+   kind = "^CustomResourceDefinition$",
+)
+k8s_yaml(helm_non_crds)
diff --git a/default.nix b/default.nix
new file mode 100644
index 00000000..1cf848c2
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,68 @@
+{ sources ? import ./nix/sources.nix # managed by https://github.com/nmattia/niv
+, nixpkgs ? sources.nixpkgs
+, pkgs ? import nixpkgs {}
+, cargo ? import ./Cargo.nix {
+    inherit nixpkgs pkgs; release = false;
+    defaultCrateOverrides = pkgs.defaultCrateOverrides // {
+      prost-build = attrs: {
+        buildInputs = [ pkgs.protobuf ];
+      };
+      tonic-reflection = attrs: {
+        buildInputs = [ pkgs.rustfmt ];
+      };
+    };
+  }
+, meta ? pkgs.lib.importJSON ./nix/meta.json
+, dockerName ? "docker.stackable.tech/sandbox/${meta.operator.name}"
+, dockerTag ? null
+}:
+rec {
+  build = cargo.allWorkspaceMembers;
+  entrypoint = build+"/bin/stackable-${meta.operator.name}";
+  crds = pkgs.runCommand "${meta.operator.name}-crds.yaml" {}
+  ''
+    ${entrypoint} crd > $out
+  '';
+
+  dockerImage = pkgs.dockerTools.streamLayeredImage {
+    name = dockerName;
+    tag = dockerTag;
+    contents = [ pkgs.bashInteractive pkgs.coreutils pkgs.util-linuxMinimal ];
+    config = {
+    Env =
+      let
+        fileRefVars = {
+          PRODUCT_CONFIG = deploy/config-spec/properties.yaml;
+        };
+      in pkgs.lib.concatLists (pkgs.lib.mapAttrsToList (env: path: pkgs.lib.optional (pkgs.lib.pathExists path) "${env}=${path}") fileRefVars);
+      Entrypoint = [ entrypoint ];
+      Cmd = [ "run" ];
+    };
+  };
+  docker = pkgs.linkFarm "listener-operator-docker" [
+    {
+      name = "load-image";
+      path = dockerImage;
+    }
+    {
+      name = "ref";
+      path = pkgs.writeText "${dockerImage.name}-image-tag" "${dockerImage.imageName}:${dockerImage.imageTag}";
+    }
+    {
+      name = "image-repo";
+      path = pkgs.writeText "${dockerImage.name}-repo" dockerImage.imageName;
+    }
+    {
+      name = "image-tag";
+      path = pkgs.writeText "${dockerImage.name}-tag" dockerImage.imageTag;
+    }
+    {
+      name = "crds.yaml";
+      path = crds;
+    }
+  ];
+
+  # need to use vendored crate2nix because of https://github.com/kolloch/crate2nix/issues/264
+  crate2nix = import sources.crate2nix {};
+  tilt = pkgs.tilt;
+}
diff --git a/nix/meta.json b/nix/meta.json
new file mode 100644
index 00000000..54787a2b
--- /dev/null
+++ b/nix/meta.json
@@ -0,0 +1 @@
+{"operator": {"name": "spark-k8s-operator", "pretty_string": "Apache Spark-on-Kubernetes", "product_string": "spark-k8s", "url": "stackabletech/spark-k8s-operator.git"}}
diff --git a/nix/sources.json b/nix/sources.json
new file mode 100644
index 00000000..6dc1f0e6
--- /dev/null
+++ b/nix/sources.json
@@ -0,0 +1,26 @@
+{
+    "crate2nix": {
+        "branch": "master",
+        "description": "nix build file generator for rust crates",
+        "homepage": "",
+        "owner": "kolloch",
+        "repo": "crate2nix",
+        "rev": "45fc83132c8c91c77a1cd61fe0c945411d1edba8",
+        "sha256": "00w9qza56xh9m98308wzfbjf135gpz6sf7b5yfharvmax1k46c5q",
+        "type": "tarball",
+        "url": "https://github.com/kolloch/crate2nix/archive/45fc83132c8c91c77a1cd61fe0c945411d1edba8.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "nixpkgs-unstable",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "747927516efcb5e31ba03b7ff32f61f6d47e7d87",
+        "sha256": "1s4xabv59r99z8vd74w3r84kkxwqggqir3b0nh3ma04mni0m40gf",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/747927516efcb5e31ba03b7ff32f61f6d47e7d87.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}
diff --git a/nix/sources.nix b/nix/sources.nix
new file mode 100644
index 00000000..9a01c8ac
--- /dev/null
+++ b/nix/sources.nix
@@ -0,0 +1,194 @@
+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+      submodules = if spec ? submodules then spec.submodules else false;
+      submoduleArg =
+        let
+          nixSupportsSubmodules = builtins.compareVersions builtins.nixVersion "2.4" >= 0;
+          emptyArgWithWarning =
+            if submodules == true
+            then
+              builtins.trace
+                (
+                  "The niv input \"${name}\" uses submodules "
+                  + "but your nix's (${builtins.nixVersion}) builtins.fetchGit "
+                  + "does not support them"
+                )
+                {}
+            else {};
+        in
+          if nixSupportsSubmodules
+          then { inherit submodules; }
+          else emptyArgWithWarning;
+    in
+      builtins.fetchGit
+        ({ url = spec.repo; inherit (spec) rev; inherit ref; } // submoduleArg);
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources: system:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${ersatz}";
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }