From 2d989ef6cb8358c6606bca5d57842e46add37480 Mon Sep 17 00:00:00 2001
From: Vincent Ambo <tazjin@tvl.su>
Date: Sun, 9 Feb 2025 12:11:11 +0300
Subject: [PATCH] refactor(ops/tvl-buildkite): add concept of small/large slots

Adds a new tagging system to Buildkite agents, where agents are tagged with
large/small slots. All agents have small slots, only some agents have large
slots. The small slots are purely informative - nothing targets them, whereas
large slots will be used for filtering agents.

This allows us to target large slots in some builds and minimise the concurrent
execution of extremely large builds, while keeping a large number of small slots
around for all the light targets.

This will need some tuning over time (also because tagging is a manual process).

Change-Id: I15aa657773ed874d84d98e55238fb31c75d4efa7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13120
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
---
 ops/modules/tvl-buildkite.nix | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/ops/modules/tvl-buildkite.nix b/ops/modules/tvl-buildkite.nix
index d9d79cd52..003a36fc6 100644
--- a/ops/modules/tvl-buildkite.nix
+++ b/ops/modules/tvl-buildkite.nix
@@ -27,10 +27,17 @@ in
 {
   options.services.depot.buildkite = {
     enable = lib.mkEnableOption description;
+
     agentCount = lib.mkOption {
       type = lib.types.int;
       description = "Number of Buildkite agents to launch";
     };
+
+    largeSlots = lib.mkOption {
+      type = lib.types.int;
+      default = cfg.agentCount;
+      description = "Number of agents with 'large=true'";
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -50,6 +57,9 @@ in
 
           tags.hostname = hostname;
 
+          # all agents support small jobs
+          tags.small = "true";
+
           runtimePackages = with pkgs; [
             bash
             coreutils
@@ -61,7 +71,9 @@ in
             jq
             nix
           ];
-        };
+        } // (lib.optionalAttrs (n <= cfg.largeSlots) {
+          tags.large = "true";
+        });
       })
       agents);