diff --git a/dnscontrol/dnsconfig.js b/dnscontrol/dnsconfig.js
index b0cec61b9..4b0b87030 100644
--- a/dnscontrol/dnsconfig.js
+++ b/dnscontrol/dnsconfig.js
@@ -59,6 +59,7 @@ var cnames = {
     "nixpkgs-update-logs": "build02",
     "nur-update": "build03",
     "prometheus": "web02",
+    "temp-cache": "build03",
 };
 
 var records = [];
diff --git a/flake.nix b/flake.nix
index d5eecd7f5..247f98996 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,9 +1,13 @@
 {
   description = "NixOS configuration of our builders";
 
-  nixConfig.extra-substituters = [ "https://nix-community.cachix.org" ];
+  nixConfig.extra-substituters = [
+    "https://nix-community.cachix.org"
+    "https://temp-cache.nix-community.org"
+  ];
   nixConfig.extra-trusted-public-keys = [
     "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+    "temp-cache.nix-community.org-1:RSXIfGjilfBsilDvj03/VnL/9qAxacBnb1YQvSdCoDc="
   ];
 
   inputs = {
diff --git a/hosts/build03/cache.nix b/hosts/build03/cache.nix
new file mode 100644
index 000000000..efd0d8645
--- /dev/null
+++ b/hosts/build03/cache.nix
@@ -0,0 +1,26 @@
+{ config, ... }:
+{
+  # temp-cache.nix-community.org-1:RSXIfGjilfBsilDvj03/VnL/9qAxacBnb1YQvSdCoDc=
+
+  sops.secrets.harmonia-key = { };
+
+  services.harmonia = {
+    enable = true;
+    signKeyPaths = [ config.sops.secrets.harmonia-key.path ];
+    settings.priority = 50; # prefer c.n.o
+  };
+
+  services.nginx.virtualHosts."temp-cache.nix-community.org" = {
+    locations."/" = {
+      extraConfig = ''
+        proxy_pass http://127.0.0.1:5000;
+        proxy_set_header Host $host;
+        proxy_redirect http:// https://;
+        proxy_http_version 1.1;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection $connection_upgrade;
+      '';
+    };
+  };
+}
diff --git a/hosts/build03/default.nix b/hosts/build03/default.nix
index d29be6414..2337781e7 100644
--- a/hosts/build03/default.nix
+++ b/hosts/build03/default.nix
@@ -2,6 +2,7 @@
 {
   imports = [
     ./builders.nix
+    ./cache.nix
     ./postgresql.nix
     inputs.self.nixosModules.buildbot
     inputs.self.nixosModules.cgroups
diff --git a/hosts/build03/secrets.yaml b/hosts/build03/secrets.yaml
index a93cd474e..18f6c3f45 100644
--- a/hosts/build03/secrets.yaml
+++ b/hosts/build03/secrets.yaml
@@ -9,6 +9,7 @@ buildbot-github-oauth-secret: ENC[AES256_GCM,data:C5P54zotOwe3u2cOsJMKEVmZVH6hrL
 buildbot-github-webhook-secret: ENC[AES256_GCM,data:AtUFcOjLivJt8np5451Wfol5s48R4vW5gJPisT+hMD7dFAvucKriQEY+mcAMqL1X6w==,iv:oBKj9XXu/4mkeH+3KkMlWSx8GnMoXwBugNuG8Uu3XtU=,tag:8cBZVE7TOJf3QEqxfsuF8g==,type:str]
 buildbot-nix-worker-password: ENC[AES256_GCM,data:TaMHVzlzuAHfTBAyqG5JJFwpG2We+wlXva3YJnNkO9KSX9PIhnRHVES72jO63AkhvfBVEg==,iv:rTpaiCYcedcsy115BEDep68Mehb6knes7OxvBrEOrUQ=,tag:dD4Hg4oR3SfpYdP1e8V2jA==,type:str]
 buildbot-effects-nix-community-infra: ENC[AES256_GCM,data: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,iv:rdLHfK4NbCaMIIhhQd2MfVf1DdKKF9Sqe4Kxuy57yok=,tag:DPxsDTLIhA0d4KPXwseL9g==,type:str]
+harmonia-key: ENC[AES256_GCM,data:J75n5ltSXTM2FcJJ2/J1zmGBdluLx5r6hk2hnvsufzhurmMd15JfZ48PXpcmmXruunjI7ESu731QsiZyXRILvCYY4n8I0TLI+MjhZkZeQMoYi+BGy+DJh+AoKdmy/uKSdZArnQU1dUBNXrAVmdjuWbF0Ca/w5oEm,iv:bM9h6TJw6gh0xLOtKTdPkABG0amTji4/692copvCHx8=,tag:b5HzLU0mtvBIF/AEnjMI+Q==,type:str]
 sops:
     age:
         - recipient: age1qg7tfjwzp6dxwkw9vej6knkhdvqre3fu7ryzsdk5ggvtdx854ycqevlwnq
@@ -65,7 +66,7 @@ sops:
             WUZQSGQyQy9halJsRTIvb1FGV08zZEEKmjlYY6epTuZKRBcVyjPvJI5XKQtP5Yag
             FMrI+M6hUeyBeCade5C+Y4eGQbt57BWLmsX7u0J1WTlkUSS5j7+wPg==
             -----END AGE ENCRYPTED FILE-----
-    lastmodified: "2025-03-31T22:39:35Z"
-    mac: ENC[AES256_GCM,data:ElmfLZnKsI6bctc8/bQIvP922g6PUVjMfvqC+jEorAkXrqzHOKKNgnglNOUCsgGwOtTNIcoc8/LWZdTlNLECssjIbKYAOXIrbH8m3tS+8eLO4iP1NfYs7xkJfjBkeYNmIxLHLX9IcIEMI5qHFNAKQpRyyIDLEmLHETCcxd7vqGs=,iv:zOycJAh3X1e+R/9XTo+hCYcpeM+5OXgXOI+QY3YXY9s=,tag:lWUd/IfLTIvIge1JhBOq5w==,type:str]
+    lastmodified: "2025-04-03T00:01:38Z"
+    mac: ENC[AES256_GCM,data:LVtM9u7yi7eCMGemQhBQG5mJ8g1iRoL+bBl4MJsvWFh/9BTP1jnMh+nfUz947CnAiPUnBpIK0EV1lxqrRT67O5bTfVReHMQfmSBUgjFqOBJEQywvGNucumGE1n/iSpzj3gwoDlWlMWmq2lzofOEQOTsbXSHCzz8nWXyZ6HxjYKQ=,iv:zxgRFZo1VTWpOYdQCEC/YMgSGMX1/sN1iKqFXEcJ+U8=,tag:2c/xd9M6VfVcMOnIMMnW+w==,type:str]
     unencrypted_suffix: _unencrypted
-    version: 3.10.0
+    version: 3.10.1
diff --git a/modules/shared/nix-daemon.nix b/modules/shared/nix-daemon.nix
index babd2d99e..771227cee 100644
--- a/modules/shared/nix-daemon.nix
+++ b/modules/shared/nix-daemon.nix
@@ -16,9 +16,13 @@ in
   nix = {
     settings.trusted-public-keys = [
       "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      "temp-cache.nix-community.org-1:RSXIfGjilfBsilDvj03/VnL/9qAxacBnb1YQvSdCoDc="
     ];
 
-    settings.substituters = [ "https://nix-community.cachix.org" ];
+    settings.substituters = [
+      "https://nix-community.cachix.org"
+      "https://temp-cache.nix-community.org"
+    ];
 
     # auto-free the /nix/store
     settings.min-free = asGB 1;