Add a function to extract your host ip

functions/what_is_my_ip/.envrc

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+use flake

functions/what_is_my_ip/Dockerfile

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+
+# syntax = docker/dockerfile:1.4
+FROM nixos/nix:2.21.1@sha256:3f6c77ee4d2c82e472e64e6cd7087241dc391421a0b42c22e6849c586d5398d9 AS builder
+
+WORKDIR /tmp/build
+RUN mkdir /tmp/nix-store-closure
+
+# ignore SC2046 because the output of nix-store -qR will never have spaces - this is safe here
+# hadolint ignore=SC2046
+RUN --mount=type=cache,target=/nix,from=nixos/nix:2.21.1,source=/nix \
+    --mount=type=cache,target=/root/.cache \
+    --mount=type=bind,target=/tmp/build \
+    <<EOF
+  nix \
+    --extra-experimental-features "nix-command flakes" \
+    --option filter-syscalls false \
+    --extra-trusted-substituters "https://cache.iog.io" \
+    --extra-trusted-public-keys "hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=" \
+    --show-trace \
+    --log-format raw \
+    build . --out-link /tmp/output/result
+  cp -R $(nix-store -qR /tmp/output/result) /tmp/nix-store-closure
+EOF
+
+FROM scratch
+
+WORKDIR /app
+
+COPY --from=builder /tmp/nix-store-closure /nix/store
+COPY --from=builder /tmp/output/ /app/
+
+ENTRYPOINT ["/app/result/bin/entrypoint"]

functions/what_is_my_ip/flake.nix

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+{
+  description = "what is my ip";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, ...}@inputs:
+
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+          };
+
+        in rec
+        {
+          packages = rec {
+
+            default = pkgs.writeShellScriptBin "entrypoint" ''
+              ${pkgs.curl}/bin/curl -s http://httpbin.org/get | \
+                  ${pkgs.jq}/bin/jq --raw-output .origin
+            '';
+          };
+        });
+}

functions/what_is_my_ip/runbook.md

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+# Background
+
+The `write_file` function has wo parameters.
+
+* `path`: is a relative path from some project_root
+* `content`: is the content that should be written into the file
+
+## Usage
+
+This function should be given a rw bind mount for the root of a project.
+
+```sh
+docker run --rm --entrypoint /app/result/bin/entrypoint vonwig/what-is-my-ip:latest
+```
+
+## Build
+
+```sh
+docker build -t vonwig/what-is-my-ip:latest .
+```
+
+```sh
+# docker:command=build
+
+docker buildx build \
+    --builder hydrobuild \
+    --platform linux/amd64,linux/arm64 \
+    --tag vonwig/what-is-my-ip:latest \
+    --file Dockerfile \
+    --push .
+docker pull vonwig/what-is-my-ip:latest
+```