Add custom nix-daemon exporter

Allows us to see which derivations are being built in realtime. It is a
bit of a hack, but it seems to work. We simply look at the environment
of the child processes of nix-daemon (usually bash) and then look for
the $name variable which should hold the current derivation being
built. Needs root to be able to read the environ file of the different
nix-daemon processes as they are owned by the nixbld* users.

See: https://discourse.nixos.org/t/query-ongoing-builds/23486
Reviewed-by: Reviewed-by: Aleix Boné <abonerib@bsc.es>

doc/2025-05-maintenance-purchase.md

@@ -1,156 +0,0 @@
-# Maintenance purchase 2025-05
-
-We need to buy some components to replace broken parts or to have spare ones for
-when they break. We also need some tools to do basic repairs.
-
-Here is the list:
-
-- 11 x Power supply DELTA DPS-750XB A (700 W) (this is critical)
-  - 57.69€/unit, 634.59€ total <https://es.aliexpress.com/item/1005004090017186.html>
-
-- 8 x RAM DDR4 2400MHz PC4-19200 ECC Registered
-  - 128.85€/pair, 515.40€ total <https://www.amazon.es/PC4-19200-REGISTERED-MEMORY-WORKSTATIONS-MOTHERBOARDS/dp/B06W9P3RKF>
-
-- 1 x Set of screwdrivers
-  - 23.99€ <https://www.amazon.es/BLOSTM-Juego-Destornilladores-Profesionales-Destornillador/dp/B09W9R8J3S>
-
-- 1 x UART adaptor
-  - 14.99€ <https://www.amazon.es/DSD-TECH-SH-U09C5-convertidor-Soporte/dp/B07WX2DSVB>
-
-- 1 x SSD SATA disk of 2 TB
-  - 135.99€ <https://www.amazon.es/Crucial-BX500-pulgadas-interno-CT2000BX500SSD101/dp/B0CCN9QWKT>
-
-Total: 1324.96 €
-
-# Rationale
-
-Below is the search procedure I followed to come up with that list.
-
-## Power supplies
-
-They are the first components to fail. We already have some problems with the
-monitoring of some power supplies. They will soon stop being manufactured, so we
-should increase out stack.
-
-Most Xeon nodes use the DELTA DPS-750XB A:
-
-    hut% sudo ipmitool fru
-    ...
-    FRU Device Description : Pwr Supply 1 FRU (ID 2)
-     Product Manufacturer  : DELTA
-     Product Name          : DPS-750XB A
-     Product Part Number   : E98791-010
-     Product Version       : 05
-     Product Serial        : XXXXXXXXXXXXXXXXX
-
-And we only have one per node. We should make the power supply redundant so we
-can tolerate it to fail without bringing down the node.
-
-They are available on Amazon, but they are very expensive (287.54 €):
-
-<https://www.amazon.es/DPS-750XB-E98791-010-alimentaci%C3%B3n-conmutada-Platinum/dp/B0DB65G4VT>
-
-On Aliexpress they are much cheaper (57.69 €):
-
-<https://es.aliexpress.com/item/1005004090017186.html>
-
-We have 11 nodes plus the login, but I'm not able to figure out which power
-supply the login is using.
-
-The login uses another one, AXX1100PCRPS, and only has one slot populated. We
-may want to also we another one, but I would need to reset the FRU and I don't
-have access to the login node. So I will leave this for Operations to deal with.
-We can live without the login if needed.
-
-## RAM DIMM
-
-The DIMM modules also experience errors, which are monitored by Linux. In some
-nodes we see non-recoverable errors that are no longer corrected by the ECC. We
-need to replace the bad modules.
-
-Having two spare modules per node would be enough to cover most problems in the
-future.
-
-> 16 GB, 2400 MHz RDIMM
-
-The module from dmidecode:
-
-    Handle 0x0026, DMI type 17, 40 bytes
-    Memory Device
-        Array Handle: 0x0020
-        Error Information Handle: Not Provided
-        Total Width: 72 bits
-        Data Width: 64 bits
-        Size: 16 GB
-        Form Factor: DIMM
-        Set: None
-        Locator: DIMM_B1
-        Bank Locator: NODE 1
-        Type: DDR4
-        Type Detail: Synchronous
-        Speed: 2400 MT/s
-        Manufacturer: Micron
-        Serial Number: XXXXXXXX
-        Asset Tag:
-        Part Number: 36ASF2G72PZ-2G3B1
-        Rank: 2
-        Configured Memory Speed: 2400 MT/s
-        Minimum Voltage: Unknown
-        Maximum Voltage: Unknown
-        Configured Voltage: Unknown
-
-Which is this module:
-
-<https://www.amazon.com/Micron-PC4-19200-DDR4-2400MHz-Registered-MTA36ASF2G72PZ-2G3B1/dp/B01KBCNEGI>
-
-But they have only one in stock. Here is more details:
-
-> 16GB PC4-19200 DDR4-2400MHz 
-
-The must have the following features:
-
-- 16 GB
-- DDR4
-- Speed at least 2400 MT/s
-- ECC
-- Registered
-- Best if from Micron
-
-I would say having 8 spare modules would be enough for now, as we only have a
-few that are currently failing. We could upgrade the modules later, as they
-don't have much risk of stopping being manufactured like the power supplies.
-
-These may work:
-
-- 1 x 16GB, 69,11€ <https://www.amazon.es/PC4-19200-REGISTRADO-SERVIDORES-Estaciones-CHIPKILL/dp/B06X42HC9N>
-
-- 2 x 16GB, 128,85€ <https://www.amazon.es/PC4-19200-REGISTERED-MEMORY-WORKSTATIONS-MOTHERBOARDS/dp/B06W9P3RKF>
-
-It is cheaper to buy them by pairs, so let's use the last one.
-
-## Screwdriver set
-
-In order to change and replace the machine parts we need a set of screwdrivers.
-Instead of having to bring my own from home, I want to have one at BSC. These
-are enough and come in a nice box so I don't lose them:
-
-<https://www.amazon.es/BLOSTM-Juego-Destornilladores-Profesionales-Destornillador/dp/B09W9R8J3S>
-
-## Serial port adaptor
-
-In order to debug problems with several components, we need to be able to plug
-to the serial port of the CPU. As we may deal with different voltages and
-pinouts, the most versatile option is to just be able to select the voltage and
-expose a pin interface.
-
-This one would do:
-
-<https://www.amazon.es/DSD-TECH-SH-U09C5-convertidor-Soporte/dp/B07WX2DSVB>
-
-## Storage for raccoon
-
-Given that we are currently using raccoon for builds too, we would need to
-increase its current storage. We only have available 270 GB, so we can benefit
-from another disk. Using 2 TiB would be plenty. This one seems enough:
-
-- 135,99€ <https://www.amazon.es/Crucial-BX500-pulgadas-interno-CT2000BX500SSD101/dp/B0CCN9QWKT>

m/hut/monitoring.nix

@@ -4,6 +4,7 @@
   imports = [
     ../module/slurm-exporter.nix
     ./gpfs-probe.nix
+    ./nix-daemon-exporter.nix
   ];
 
   age.secrets.grafanaJungleRobotPassword = {
@@ -108,6 +109,7 @@
             "127.0.0.1:${toString config.services.prometheus.exporters.smartctl.port}"
             "127.0.0.1:9341" # Slurm exporter
             "127.0.0.1:9966" # GPFS custom exporter
+            "127.0.0.1:9999" # Nix-daemon custom exporter
             "127.0.0.1:${toString config.services.prometheus.exporters.blackbox.port}"
           ];
         }];

m/hut/nix-daemon-builds.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+# Locate nix daemon pid
+nd=$(pgrep -o nix-daemon)
+
+# Locate children of nix-daemon
+pids1=$(tr ' ' '\n' < "/proc/$nd/task/$nd/children")
+
+# For each children, locate 2nd level children
+pids2=$(echo "$pids1" | xargs -I @ /bin/sh -c 'cat /proc/@/task/*/children' | tr ' ' '\n')
+
+cat <<EOF
+HTTP/1.1 200 OK
+Content-Type: text/plain; version=0.0.4; charset=utf-8; escaping=values
+
+# HELP nix_daemon_build Nix daemon derivation build state.
+# TYPE nix_daemon_build gauge
+EOF
+
+for pid in $pids2; do
+  name=$(cat /proc/$pid/environ 2>/dev/null | tr '\0' '\n' | rg "^name=(.+)" - --replace '$1' | tr -dc ' [:alnum:]_\-\.')
+  user=$(ps -o uname= -p "$pid")
+  if [ -n "$name" -a -n "$user" ]; then
+    printf 'nix_daemon_build{user="%s",name="%s"} 1\n' "$user" "$name"
+  fi
+done

m/hut/nix-daemon-exporter.nix

@@ -0,0 +1,23 @@
+{ pkgs, config, lib, ... }:
+let
+  script = pkgs.runCommand "nix-daemon-exporter.sh" { }
+    ''
+      cp ${./nix-daemon-builds.sh} $out;
+      chmod +x $out
+    ''
+  ;
+in
+{
+  systemd.services.nix-daemon-exporter = {
+    description = "Daemon to export nix-daemon metrics";
+    path = [ pkgs.procps pkgs.ripgrep ];
+    wantedBy = [ "default.target" ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${pkgs.socat}/bin/socat TCP4-LISTEN:9999,fork EXEC:${script}";
+      # Needed root to read the environment, potentially unsafe
+      User = "root";
+      Group = "root";
+    };
+  };
+}