promtail: add basic log shipping configuration

This automatically enables promtail when a Loki server is present in
the same resource group. Currently only a single Loki server is
supported.

PL-132981

nixos/platform/default.nix

@@ -34,6 +34,7 @@ in {
  ./monitoring.nix
  ./network.nix
  ./packages.nix
+ ./promtail.nix
  ./shell.nix
  ./static.nix
  ./syslog.nix

nixos/platform/promtail.nix

@@ -0,0 +1,51 @@
+{ lib, config, ... }:
+
+let
+ enc = config.flyingcircus.enc;
+ fclib = config.fclib;
+
+ # XXX support multiple loki servers. the upstream docs note: "It is
+ # generally recommended to run multiple Promtail clients in parallel
+ # if you want to send to multiple remote Loki instances."
+ lokiServer = fclib.findOneService "loki-collector";
+in
+{
+ config = lib.mkIf (!builtins.isNull lokiServer) {
+ services.promtail = {
+ enable = true;
+ configuration = {
+ # don't expose the http and grpc api
+ server.disable = true;
+
+ clients = [{
+ url = "http://${lokiServer.address}:3100/loki/api/v1/push";
+ }];
+
+ scrape_configs = [{
+ job_name = "systemd-journal";
+ journal = {
+ json = true;
+ # there are server side limits to how many labels loki
+ # will accept on log lines. consider them a scarce
+ # resource and use them sparingly.
+ labels = {
+ resource_group = enc.parameters.resource_group;
+ location = enc.parameters.location;
+ hostname = config.networking.hostName;
+ };
+ };
+ relabel_configs = [
+ {
+ source_labels = [ "__journal__systemd_unit" ];
+ target_label = "systemd_unit";
+ }
+ {
+ source_labels = [ "__journal_syslog_identifier" ];
+ target_label = "syslog_identifier";
+ }
+ ];
+ }];
+ };
+ };
+ };
+}