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Author SHA1 Message Date
cf2210ec77 Another attempt at fixing the NFS race. 2025-10-24 13:59:39 +01:00
1dc219d08f Install killall everywhere. 2025-10-24 11:56:47 +01:00
3 changed files with 76 additions and 17 deletions

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@@ -3,6 +3,7 @@
environment.systemPackages = with pkgs; [
age
file
killall
lm_sensors # TODO: this shouldn't be installed on cloud nodes
nodejs_20 # TODO: this is for one job on nomad, it should just be a dependency there
neovim

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@@ -4,14 +4,17 @@
# Mounts from data-services.service.consul (Consul DNS for automatic failover)
# The NFS server registers itself in Consul, so this will automatically
# point to whichever host is currently running the NFS server
#
# Uses persistent mount (not automount) with nofail to prevent blocking boot.
# The mount is established at boot time and persists - no auto-unmount.
# This prevents issues with Docker bind mounts seeing empty automount stubs.
fileSystems."/data/services" = {
device = "data-services.service.consul:/persist/services";
fsType = "nfs";
options = [
"x-systemd.automount" # Auto-mount on access
"noauto" # Don't mount at boot (automount handles it)
"x-systemd.idle-timeout=60" # Unmount after 60s of inactivity
"nofail" # Don't block boot if mount fails
"x-systemd.mount-timeout=30s" # Timeout for mount attempts
"_netdev" # Network filesystem (wait for network)
];
};

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@@ -59,20 +59,75 @@ in
extraSettingsPaths = [ "/etc/nomad-alo.json" ];
};
# Fix race condition between NFS automount and Docker bind mounts:
# Without this, Docker can bind-mount the empty automount stub directory
# before NFS actually mounts, causing permission errors and missing data.
# - RequiresMountsFor: tells systemd that Nomad depends on /data/services
# - ExecStartPre: triggers the automount before Nomad starts
# Note: boot will still succeed if NFS is unavailable (Nomad just won't start)
# TODO: NFS mount uses Consul DNS which resolves to an IP at mount time.
# If the NFS server moves to a different IP, the mount becomes stale
# and needs to be remounted. Consider using a VIP or implementing
# a health check that remounts on staleness detection.
# NFS mount dependency configuration for Nomad:
#
# Problem: Docker bind mounts need the real NFS mount, not an empty stub.
# If Nomad starts before NFS is mounted, containers get empty directories.
#
# Solution: Use soft dependencies (wants/after) with health-checking recovery.
# - wants: Nomad wants the mount, but won't be killed if it goes away
# - after: Nomad waits for mount to be attempted before starting
# - ExecStartPre with findmnt: Blocks Nomad start until mount is actually active
#
# This prevents Docker race conditions while allowing:
# - Boot to proceed if NFS unavailable (Nomad fails to start, systemd retries)
# - Nomad to keep running if NFS temporarily fails (containers may error)
# - Recovery service to auto-restart Nomad when NFS comes back or becomes stale
#
# Note: Mount uses Consul DNS which resolves at mount time. If NFS server
# moves to different IP, mount becomes stale and needs remount.
# The recovery service handles this by detecting stale mounts and restarting Nomad.
systemd.services.nomad = {
wants = [ "network-online.target" ];
unitConfig.RequiresMountsFor = [ "/data/services" ];
serviceConfig.ExecStartPre = "${pkgs.coreutils}/bin/ls /data/services";
wants = [ "network-online.target" "data-services.mount" ];
after = [ "data-services.mount" ];
serviceConfig.ExecStartPre = "${pkgs.util-linux}/bin/findmnt --mountpoint /data/services";
};
# Recovery service: automatically restart Nomad when NFS mount needs attention
# This handles scenarios where:
# - NFS server was down during boot (mount failed, Nomad hit start-limit)
# - NFS server failed over to different host with new IP (mount went stale)
# - Network outage temporarily broke the mount
#
# The timer runs every 30s and checks:
# 1. Is mount healthy (exists and accessible)?
# 2. If mount is stale/inaccessible → restart Nomad (triggers remount)
# 3. If mount is healthy but Nomad failed → restart Nomad (normal recovery)
systemd.services.nomad-mount-watcher = {
description = "Restart Nomad when NFS mount needs attention";
serviceConfig = {
Type = "oneshot";
ExecStart = pkgs.writeShellScript "nomad-mount-watcher" ''
# Check if mount point exists
if ! ${pkgs.util-linux}/bin/findmnt --mountpoint /data/services >/dev/null 2>&1; then
exit 0 # Mount not present, nothing to do
fi
# Check if mount is actually accessible (not stale)
# Use timeout to avoid hanging on stale NFS mounts
if ! ${pkgs.coreutils}/bin/timeout 5s ${pkgs.coreutils}/bin/stat /data/services >/dev/null 2>&1; then
echo "NFS mount is stale or inaccessible. Restarting Nomad to trigger remount..."
${pkgs.systemd}/bin/systemctl restart nomad.service
exit 0
fi
# Mount is healthy - check if Nomad needs recovery
if ${pkgs.systemd}/bin/systemctl is-failed nomad.service >/dev/null 2>&1; then
echo "NFS mount is healthy but Nomad is failed. Restarting Nomad..."
${pkgs.systemd}/bin/systemctl restart nomad.service
fi
'';
};
};
systemd.timers.nomad-mount-watcher = {
description = "Timer for Nomad mount watcher";
wantedBy = [ "timers.target" ];
timerConfig = {
OnBootSec = "1min"; # First run 1min after boot
OnUnitActiveSec = "30s"; # Then every 30s
Unit = "nomad-mount-watcher.service";
};
};
environment.etc."nomad-alo.json".text = builtins.toJSON {