diff --git a/services/comms/guest-register-deployment.yaml b/services/comms/guest-register-deployment.yaml
index 2888033..04a0018 100644
--- a/services/comms/guest-register-deployment.yaml
+++ b/services/comms/guest-register-deployment.yaml
@@ -23,6 +23,15 @@ spec:
         app.kubernetes.io/name: matrix-guest-register
     spec:
       serviceAccountName: comms-vault
+      hostAliases:
+        - ip: "10.43.36.27"
+          hostnames:
+            - "matrix-authentication-service"
+            - "matrix-authentication-service.comms.svc.cluster.local"
+        - ip: "10.43.216.45"
+          hostnames:
+            - "othrys-synapse-matrix-synapse"
+            - "othrys-synapse-matrix-synapse.comms.svc.cluster.local"
       securityContext:
         runAsNonRoot: true
         runAsUser: 10001
diff --git a/services/comms/helmrelease.yaml b/services/comms/helmrelease.yaml
index 90a20ae..b907d38 100644
--- a/services/comms/helmrelease.yaml
+++ b/services/comms/helmrelease.yaml
@@ -204,6 +204,15 @@ spec:
                   spec:
                     serviceAccountName: comms-vault
                     automountServiceAccountToken: true
+                    hostAliases:
+                      - ip: "10.43.150.98"
+                        hostnames:
+                          - "othrys-synapse-redis-master"
+                          - "othrys-synapse-redis-master.comms.svc.cluster.local"
+                      - ip: "10.43.36.27"
+                        hostnames:
+                          - "matrix-authentication-service"
+                          - "matrix-authentication-service.comms.svc.cluster.local"
                     containers:
                       - name: synapse
                         command:
diff --git a/services/comms/mas-deployment.yaml b/services/comms/mas-deployment.yaml
index 0ab2071..7c4e8e4 100644
--- a/services/comms/mas-deployment.yaml
+++ b/services/comms/mas-deployment.yaml
@@ -61,6 +61,11 @@ spec:
     spec:
       enableServiceLinks: false
       serviceAccountName: comms-vault
+      hostAliases:
+        - ip: "10.43.216.45"
+          hostnames:
+            - "othrys-synapse-matrix-synapse"
+            - "othrys-synapse-matrix-synapse.comms.svc.cluster.local"
       nodeSelector:
         hardware: rpi5
       affinity: