Introduce mkBinaryCache function

2 files changed, 50 insertions, 0 deletions

diff --git a/doc/builders/images.xml b/doc/builders/images.xml
index 7d06130e3eca2..a4661ab5a7af7 100644
--- a/doc/builders/images.xml
+++ b/doc/builders/images.xml
@@ -11,4 +11,5 @@
  <xi:include href="images/snaptools.section.xml" />
  <xi:include href="images/portableservice.section.xml" />
  <xi:include href="images/makediskimage.section.xml" />
+ <xi:include href="images/binarycache.section.xml" />
 </chapter>
diff --git a/doc/builders/images/binarycache.section.md b/doc/builders/images/binarycache.section.md
new file mode 100644
index 0000000000000..71dc26311cf02
--- /dev/null
+++ b/doc/builders/images/binarycache.section.md
@@ -0,0 +1,49 @@
+# pkgs.mkBinaryCache {#sec-pkgs-binary-cache}
+
+`pkgs.mkBinaryCache` is a function for creating Nix flat-file binary caches. Such a cache exists as a directory on disk, and can be used as a Nix substituter by passing `--substituter file:///path/to/cache` to Nix commands.
+
+Nix packages are most commonly shared between machines using [HTTP, SSH, or S3](https://nixos.org/manual/nix/stable/package-management/sharing-packages.html), but a flat-file binary cache can still be useful in some situations. For example, you can copy it directly to another machine, or make it available on a network file system. It can also be a convenient way to make some Nix packages available inside a container via bind-mounting.
+
+Note that this function is meant for advanced use-cases. The more idiomatic way to work with flat-file binary caches is via the [nix-copy-closure](https://nixos.org/manual/nix/stable/command-ref/nix-copy-closure.html) command. You may also want to consider [dockerTools](#sec-pkgs-dockerTools) for your containerization needs.
+
+## Example
+
+The following derivation will construct a flat-file binary cache containing the closure of `hello`.
+
+```nix
+mkBinaryCache {
+  rootPaths = [hello];
+}
+```
+
+- `rootPaths` specifies a list of root derivations. The transitive closure of these derivations' outputs will be copied into the cache.
+
+Here's an example of building and using the cache.
+
+Build the cache on one machine, `host1`:
+
+```shellSession
+nix-build -E 'with import <nixpkgs> {}; mkBinaryCache { rootPaths = [hello]; }'
+```
+
+```shellSession
+/nix/store/cc0562q828rnjqjyfj23d5q162gb424g-binary-cache
+```
+
+Copy the resulting directory to the other machine, `host2`:
+
+```shellSession
+scp result host2:/tmp/hello-cache
+```
+
+Build the derivation using the flat-file binary cache on the other machine, `host2`:
+```shellSession
+nix-build -A hello '<nixpkgs>' \
+  --option require-sigs false \
+  --option trusted-substituters file:///tmp/hello-cache \
+  --option substituters file:///tmp/hello-cache
+```
+
+```shellSession
+/nix/store/gl5a41azbpsadfkfmbilh9yk40dh5dl0-hello-2.12.1
+```