2024-04-21

1 files changed, 135 insertions, 0 deletions

diff --git a/modules/promtail.nix b/modules/promtail.nix
new file mode 100644
index 0000000..65d88d4
--- /dev/null
+++ b/modules/promtail.nix
@@ -0,0 +1,135 @@
+{
+  config,
+  lib,
+  this,
+  ...
+}:
+with lib;
+let
+  cfg = config.nixfiles.modules.promtail;
+in
+{
+  options.nixfiles.modules.promtail = {
+    enable = mkEnableOption "Promtail";
+
+    port = mkOption {
+      description = "Port.";
+      type = with types; port;
+      default = 30181;
+    };
+
+    loki.url = mkOption {
+      description = "Address of a listening Loki service.";
+      type = with types; str;
+      default = "https://${config.nixfiles.modules.loki.domain}";
+    };
+
+    filters = mkOption {
+      description = ''Filters to use with "scrape_config.pipeline_stages".'';
+      type = with types; listOf attrs;
+      default = [ ];
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.promtail = {
+      enable = true;
+
+      configuration = {
+        server = rec {
+          http_listen_address = this.wireguard.ipv4.address;
+          http_listen_port = cfg.port;
+
+          grpc_listen_address = this.wireguard.ipv4.address;
+          grpc_listen_port = http_listen_port + 1;
+
+          log_level = "warn";
+        };
+
+        clients = [
+          {
+            url = "${cfg.loki.url}/loki/api/v1/push";
+            batchwait = "30s";
+            batchsize = 100000;
+            external_labels.host_id = config.networking.hostId;
+          }
+        ];
+
+        positions = {
+          filename = "/tmp/positions.yaml";
+          sync_period = "30s";
+          ignore_invalid_yaml = true;
+        };
+
+        scrape_configs = [
+          {
+            job_name = "journal";
+            journal.max_age = "24h";
+            relabel_configs =
+              map
+                (
+                  n:
+                  let
+                    label = toLower n;
+                  in
+                  {
+                    source_labels = [ "__journal_${label}" ];
+                    target_label = if hasPrefix "_" label then substring 1 (stringLength label - 1) label else label;
+                  }
+                )
+                [
+                  # Derived from systemd.journal fields[1].
+                  #
+                  # [1]: https://github.com/coreos/go-systemd/blob/main/sdjournal/journal.go#L335
+                  # [1]: https://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html
+
+                  "MESSAGE"
+                  # "MESSAGE_ID"
+                  "PRIORITY"
+                  # "CODE_FILE"
+                  # "CODE_LINE"
+                  # "CODE_FUNC"
+                  # "ERRNO"
+                  "SYSLOG_FACILITY"
+                  "SYSLOG_IDENTIFIER"
+                  # "SYSLOG_PID"
+                  # "_PID"
+                  # "_UID"
+                  # "_GID"
+                  # "_COMM"
+                  # "_EXE"
+                  "_CMDLINE"
+                  # "_CAP_EFFECTIVE"
+                  # "_AUDIT_SESSION"
+                  # "_AUDIT_LOGINUID"
+                  # "_SYSTEMD_CGROUP"
+                  # "_SYSTEMD_SESSION"
+                  # "_SYSTEMD_UNIT"
+                  # "_SYSTEMD_USER_UNIT"
+                  # "_SYSTEMD_OWNER_UID"
+                  # "_SYSTEMD_SLICE"
+                  # "_SELINUX_CONTEXT"
+                  # "_SOURCE_REALTIME_TIMESTAMP"
+                  # "_BOOT_ID"
+                  # "_MACHINE_ID"
+                  "_HOSTNAME"
+                  # "_TRANSPORT"
+                  # "__CURSOR"
+                  # "__REALTIME_TIMESTAMP"
+                  # "__MONOTONIC_TIMESTAMP"
+                ]
+              ++ [
+                {
+                  # This is weird. I can't find where is this defined in the
+                  # source code but apparently it exists.
+                  source_labels = [ "__journal_priority_keyword" ];
+                  target_label = "level";
+                }
+              ];
+            pipeline_stages = cfg.filters;
+          }
+        ];
+      };
+    };
+  };
+}