crowdsec: switch to Docker container with native firewall bouncer

Replaces the incomplete nixpkgs NixOS module with the official
CrowdSec Docker image for the LAPI, while keeping the firewall
bouncer as a native systemd service. API key is read from
/var/lib/secrets/crowdsec-bouncer-key at start time so it
never enters the Nix store.

https://claude.ai/code/session_01PwAXuaoJx7qD5FhVLsn7Sn

services/crowdsec.nix

@@ -1,43 +1,112 @@
 { config, lib, pkgs, ... }:
+
+let
+  # Acquisition config is written to the host config dir before the container
+  # starts, so it persists across container restarts and reflects Nix config.
+  acquisYaml = ''
+    - source: journalctl
+      journalctl_filter:
+        - "-u"
+        - "sshd"
+      labels:
+        type: syslog
+  '';
+
+  # Generates /run/crowdsec-bouncer/config.yaml at service start, injecting the
+  # API key from /var/lib/secrets/crowdsec-bouncer-key without it ever entering
+  # the Nix store. See services/crowdsec.md for key setup instructions.
+  bouncerPreStart = pkgs.writeShellScript "crowdsec-bouncer-prestart" ''
+    set -euo pipefail
+
+    KEY_FILE=/var/lib/secrets/crowdsec-bouncer-key
+    if [ ! -f "$KEY_FILE" ]; then
+      echo "ERROR: $KEY_FILE not found. See services/crowdsec.md for setup steps." >&2
+      exit 1
+    fi
+
+    API_KEY=$(cat "$KEY_FILE")
+
+    cat > /run/crowdsec-bouncer/config.yaml << EOF
+    mode: nftables
+    pid_dir: /run/crowdsec-bouncer/
+    update_frequency: 10s
+    log_mode: stdout
+    log_level: info
+    api_url: http://127.0.0.1:8080
+    api_key: $API_KEY
+    disable_ipv6: false
+    deny_action: DROP
+    deny_log: false
+    nftables:
+      ipv4:
+        enabled: true
+        set-only: false
+        table: crowdsec
+        chain: crowdsec-chain
+      ipv6:
+        enabled: true
+        set-only: false
+        table: crowdsec6
+        chain: crowdsec-chain6
+    EOF
+  '';
+in
 {
   config = lib.mkIf (config.networking.hostName == "FredOS-Mediaserver") {
-    services.crowdsec = {
-      enable = true;
-      autoUpdateService = true;
 
-      # Install detection collections on first boot
-      hub.collections = [ "crowdsecurity/linux" "crowdsecurity/sshd" ];
+    virtualisation.docker.enable = true;
+    virtualisation.oci-containers.backend = "docker";
 
-      settings = {
-        # Enable the Local API server (required for bouncer registration)
-        general.api.server.enable = true;
-        # Where the LAPI client credentials will be written on first boot
-        lapi.credentialsFile = "/var/lib/crowdsec/state/lapi-credentials.yaml";
-      };
-
-      localConfig.acquisitions = [
-        # SSH brute-force detection
-        {
-          source = "journalctl";
-          journalctl_filter = [ "-u" "sshd" ];
-          labels.type = "syslog";
-        }
+    # CrowdSec LAPI runs as a Docker container.
+    # Collections are installed on first boot via the COLLECTIONS env var.
+    # Journals are mounted read-only so CrowdSec can run journalctl inside the container.
+    virtualisation.oci-containers.containers.crowdsec = {
+      image = "crowdsecurity/crowdsec:latest";
+      ports = [ "127.0.0.1:8080:8080" ];
+      volumes = [
+        "/var/lib/crowdsec/data:/var/lib/crowdsec/data"
+        "/var/lib/crowdsec/config:/etc/crowdsec"
+        "/var/log/journal:/var/log/journal:ro"
+        "/run/log/journal:/run/log/journal:ro"
+        "/etc/machine-id:/etc/machine-id:ro"
       ];
+      environment = {
+        COLLECTIONS = "crowdsecurity/linux crowdsecurity/sshd";
+      };
     };
 
-    # The bouncer-register service uses raw cscli (no -c flag), so it looks for
-    # config at /etc/crowdsec/config.yaml. Symlink the Nix-generated config there.
+    # Write acquisition config into the host config dir before the container starts.
+    systemd.services.docker-crowdsec.preStart = ''
+      mkdir -p /var/lib/crowdsec/config/acquis.d
+      cat > /var/lib/crowdsec/config/acquis.d/nixos.yaml << 'ACQUIS'
+      ${acquisYaml}
+      ACQUIS
+    '';
+
     systemd.tmpfiles.rules = [
-      "L+ /etc/crowdsec/config.yaml - - - - ${(pkgs.formats.yaml { }).generate "crowdsec.yaml" config.services.crowdsec.settings.general}"
+      "d /var/lib/crowdsec/data   0750 root root -"
+      "d /var/lib/crowdsec/config 0750 root root -"
+      "d /var/lib/secrets         0700 root root -"
     ];
 
-    # Ensure /var/lib/crowdsec exists before crowdsec starts (race with tmpfiles-resetup)
-    systemd.services.crowdsec.after = [ "systemd-tmpfiles-resetup.service" ];
+    # Firewall bouncer runs natively. API key is injected at start time from
+    # /var/lib/secrets/crowdsec-bouncer-key — see services/crowdsec.md.
+    systemd.services.crowdsec-firewall-bouncer = {
+      description = "CrowdSec nftables firewall bouncer";
+      after = [ "network.target" "docker-crowdsec.service" ];
+      wants = [ "docker-crowdsec.service" ];
+      wantedBy = [ "multi-user.target" ];
 
-    # Firewall bouncer — auto-registers to local CrowdSec LAPI
-    services.crowdsec-firewall-bouncer = {
-      enable = true;
-      settings.api_url = "http://127.0.0.1:8080";
+      serviceConfig = {
+        Type = "simple";
+        RuntimeDirectory = "crowdsec-bouncer";
+        ExecStartPre = bouncerPreStart;
+        ExecStart = "${pkgs.crowdsec-firewall-bouncer}/bin/cs-firewall-bouncer -c /run/crowdsec-bouncer/config.yaml";
+        Restart = "on-failure";
+        RestartSec = "5s";
+        AmbientCapabilities = [ "CAP_NET_ADMIN" "CAP_NET_RAW" ];
+        CapabilityBoundingSet = [ "CAP_NET_ADMIN" "CAP_NET_RAW" ];
+      };
     };
   };
 }