Add ICMP probes

These probes check if we can reach several targets via ICMP, which is
not proxied, so they can be used to see if ICMP forwarding is working in
the login node.

In particular, we test if we can reach the Google (8.8.8.8) and
Cloudflare (1.1.1.1) DNS servers, the BSC gateway which responds to ping
only from the intranet and the login node (ssfhead).

Reviewed-By: Aleix Roca Nonell <aleix.rocanonell@bsc.es>

m/hut/blackbox.yml

@@ -121,12 +121,11 @@ modules:
         - expect: "PING :([^ ]+)"
           send: "PONG ${1}"
         - expect: "^:[^ ]+ 001"
-  icmp_example:
+  icmp:
     prober: icmp
     timeout: 5s
     icmp:
       preferred_ip_protocol: "ip4"
-      source_ip_address: "127.0.0.1"
   dns_udp_example:
     prober: dns
     timeout: 5s

m/hut/monitoring.nix

@@ -100,7 +100,7 @@
         }];
       }
       {
-        job_name = "blackbox";
+        job_name = "blackbox-http";
         metrics_path = "/probe";
         params = { module = [ "http_2xx" ]; };
         static_configs = [{
@@ -128,6 +128,36 @@
           }
         ];
       }
+      {
+        job_name = "blackbox-icmp";
+        metrics_path = "/probe";
+        params = { module = [ "icmp" ]; };
+        static_configs = [{
+          targets = [
+            "1.1.1.1"
+            "8.8.8.8"
+            "ssfhead"
+            "gw.bsc.es"
+          ];
+        }];
+        relabel_configs = [
+          {
+            # Takes the address and sets it in the "target=<xyz>" URL parameter
+            source_labels = [ "__address__" ];
+            target_label = "__param_target";
+          }
+          {
+            # Sets the "instance" label with the remote host we are querying
+            source_labels = [ "__param_target" ];
+            target_label = "instance";
+          }
+          {
+            # Shows the host target address instead of the blackbox address
+            target_label = "__address__";
+            replacement = "127.0.0.1:${toString config.services.prometheus.exporters.blackbox.port}";
+          }
+        ];
+      }
       {
         # Scrape the IPMI info of the hosts remotely via LAN
         job_name = "ipmi-lan";