chore(nix): Increase maximum number of layers to 96

This uses a significantly larger percentage of the total available
layers (125) than before, which means that cache hits for layers
become more likely between images.

2 files changed, 5 insertions, 6 deletions

diff --git a/tools/nixery/build-registry-image.nix b/tools/nixery/build-registry-image.nix
index 6a5312b444d0..255f1ca9b1d0 100644
--- a/tools/nixery/build-registry-image.nix
+++ b/tools/nixery/build-registry-image.nix
@@ -29,11 +29,10 @@
   packages ? "[]",
   # Optional bash script to run on the files prior to fixturizing the layer.
   extraCommands ? "", uid ? 0, gid ? 0,
-  # Docker's lowest maximum layer limit is 42-layers for an old
-  # version of the AUFS graph driver. We pick 24 to ensure there is
-  # plenty of room for extension. I believe the actual maximum is
-  # 128.
-  maxLayers ? 24,
+  # Docker's modern image storage mechanisms have a maximum of 125
+  # layers. To allow for some extensibility (via additional layers),
+  # the default here is set to something a little less than that.
+  maxLayers ? 96,
 
   # Configuration for which package set to use when building.
   #
diff --git a/tools/nixery/default.nix b/tools/nixery/default.nix
index 4f0b14c90394..092c76e9c5b9 100644
--- a/tools/nixery/default.nix
+++ b/tools/nixery/default.nix
@@ -30,7 +30,6 @@ rec {
     # or similar (as other required files will not be included), but
     # buildGoPackage requires a package path.
     goPackagePath = "github.com/google/nixery";
-
     goDeps = ./go-deps.nix;
     src    = ./.;
 
@@ -116,6 +115,7 @@ rec {
   in dockerTools.buildLayeredImage {
     name = "nixery";
     config.Cmd = ["${nixery-launch-script}/bin/nixery"];
+    maxLayers = 96;
     contents = [
       cacert
       coreutils