fix: [alert] AlertmanagerClusterFailedToSendAlerts (monitoring) (#649)

Reviewed-on: k.renner/homelab#646

kubernetes/apps/monitoring/helmrelease-prometheus.yaml

@@ -275,8 +275,11 @@ spec:
           - alertmanager-smtp
       # SMTP via Proton submission (smtp.protonmail.ch:587 STARTTLS).
       # The Proton SMTP token is a per-account credential generated in
-      # the Proton webapp (Settings -> IMAP/SMTP) and lives in the
-      # alertmanager-smtp SOPS-encrypted Secret. Outbound 587 from the
+      # the Proton webapp (Settings -> IMAP/SMTP). It is stored in
+      # OpenBao at apps/monitoring/alertmanager-smtp and projected into
+      # the alertmanager-smtp Secret by
+      # ./alertmanager-smtp-externalsecret.yaml — rotating the token
+      # means updating OpenBao, not this repo. Outbound 587 from the
       # monitoring ns is not blocked by any CNP today.
       config:
         global:

kubernetes/infrastructure/openbao/helmrelease.yaml

@@ -42,12 +42,28 @@ spec:
       # the agent-injector mutating webhook is unused surface.
       enabled: false
     server:
-      # Single-node raft (not standalone/file) so we get `bao operator raft
-      # snapshot` as a consistent backup primitive. TLS terminates at the
-      # Traefik ingress; in-cluster traffic is plain HTTP.
+      # Raft (not standalone/file) for two reasons: `bao operator raft
+      # snapshot` as a consistent backup primitive, and real HA across three
+      # nodes. TLS terminates at the Traefik ingress; in-cluster traffic is
+      # plain HTTP.
       ha:
         enabled: true
-        replicas: 1
+        # Three, not two. Raft needs a quorum, and the quorum of two is two —
+        # a two-replica cluster tolerates no failures at all and would stop
+        # the moment one pod is sealed or rescheduled, which is worse than
+        # the single replica it replaced. Three tolerates one.
+        #
+        # What this buys, and what it does not: a node drain seals the replica
+        # on it, and raft elects a new leader from the remaining standbys
+        # within seconds, so the service does not go down. It does NOT remove
+        # the manual unseal — a sealed server can neither serve requests nor
+        # act as standby, so that replica stays out until someone unseals it.
+        #
+        # The consequence for rolling node maintenance is worth stating: a
+        # Talos upgrade drains all three nodes in turn, sealing each replica
+        # as it goes. Unseal each one as it comes back, or the third drain
+        # takes the last unsealed replica with it and quorum is lost anyway.
+        replicas: 3
         raft:
           enabled: true
           setNodeId: true
@@ -65,8 +81,32 @@ spec:
               cluster_address = "[::]:8201"
             }
 
+            # retry_join is what makes a replica join the existing raft
+            # cluster instead of coming up as an isolated, uninitialized
+            # node. Without it, scaling the StatefulSet produces pods that
+            # never become peers and would each need a manual
+            # `bao operator raft join`.
+            #
+            # All three peers are listed on every node, including the node
+            # itself. That is deliberate: the stanza is a list of possible
+            # leaders, a node ignores its own entry, and listing all three
+            # means the set is identical on every replica and stays correct
+            # regardless of which pod currently leads.
+            #
+            # Addressed through the headless service, so each entry resolves
+            # to one specific pod rather than load-balancing across them.
             storage "raft" {
               path = "/openbao/data"
+
+              retry_join {
+                leader_api_addr = "http://openbao-0.openbao-internal:8200"
+              }
+              retry_join {
+                leader_api_addr = "http://openbao-1.openbao-internal:8200"
+              }
+              retry_join {
+                leader_api_addr = "http://openbao-2.openbao-internal:8200"
+              }
             }
 
             service_registration "kubernetes" {}

kubernetes/infrastructure/openbao/snapshot-cronjob.yaml

@@ -53,7 +53,13 @@ spec:
               command: ["/bin/sh", "-ec"]
               args:
                 - |
-                  export BAO_ADDR=http://openbao.openbao.svc.cluster.local:8200
+                  # openbao-active, not openbao: with more than one replica
+                  # the plain service selects any pod, and a raft snapshot has
+                  # to be taken against the leader. Standbys forward ordinary
+                  # requests, but this is not one to leave to chance — the
+                  # active service selects the leader by label, so the
+                  # snapshot is always taken where it is consistent.
+                  export BAO_ADDR=http://openbao-active.openbao.svc.cluster.local:8200
                   BAO_TOKEN=$(bao write -field=token auth/kubernetes/login \
                     role=openbao-snapshot \
                     jwt="$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)")