From dcb65d822501b8bec3a1854f068e333316255474 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Fri, 8 Apr 2022 19:34:52 -0400
Subject: [PATCH] Configure journald to discard logs before they're older than
30 days
---
.../modules/monitoring/exporters/promtail.nix | 23 +++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/nixos/modules/monitoring/exporters/promtail.nix b/nixos/modules/monitoring/exporters/promtail.nix
index 83de3250..d0a49971 100644
--- a/nixos/modules/monitoring/exporters/promtail.nix
+++ b/nixos/modules/monitoring/exporters/promtail.nix
@@ -32,6 +32,29 @@ in {
config = lib.mkIf cfg.enable {
services.promtail.enable = true;
networking.firewall.interfaces.monitoringvpn.allowedTCPPorts = [ 9080 ];
+
+ # Since we'll send our journald logs elsewhere, we don't need to keep them
+ # here for very long. Keep them for a *little* while just to provide some
+ # context in case someone ends up looking at the logs on the system itself
+ # but generally suppose that people will look at Loki instead.
+ services.journald.extraConfig = ''
+ # This tells journald it can discard log files that contain only log
+ # entries that are older than 29 days.
+ MaxRetentionSec=29day
+
+ # This tells journald to start a new log file once a day. Together with
+ # the MaxRetentionSec setting, this means that entries are kept for
+ # between 29 and 30 days (plus whatever scheduling slop journald has in
+ # enforcing these limits).
+ #
+ # https://www.freedesktop.org/software/systemd/man/journald.conf.html
+ # for further details about these options.
+ #
+ # A maximum retention of 30 days conforms to the published log retention
+ # policy.
+ MaxFileSec=1day
+ '';
+
services.promtail.configuration = {
server = {
http_listen_port = 9080; # Using /metrics for health check
--
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