POC: Supporting k3s-ansible with external database (#339)

* POC: Supporting k3s-ansible with external database

Signed-off-by: Peter Klijn <pjmklijn@gmail.com>

README.md

@@ -63,6 +63,30 @@ Start provisioning of the cluster using the following command:
 ansible-playbook playbooks/site.yml -i inventory.yml
 ```
 
+### Using an external database
+
+If an external database is preferred, this can be achieved by passing the `--datastore-endpoint` as an extra server argument as well as setting the `use_external_database` flag to true.
+
+```bash
+k3s_cluster:
+  children:
+    server:
+      hosts:
+        192.16.35.11:
+        192.16.35.12:
+    agent:
+      hosts:
+        192.16.35.13:
+
+  vars:
+    use_external_database: true
+    extra_server_args: "--datastore-endpoint=postgres://username:password@hostname:port/database-name"
+```
+
+The `use_external_database` flag is required when more than one server is defined, as otherwise an embedded etcd cluster will be created instead.
+
+The format of the datastore-endpoint parameter is dependent upon the datastore backend, please visit the [K3s datastore endpoint format](https://docs.k3s.io/datastore#datastore-endpoint-format-and-functionality) for details on the format and supported datastores.
+
 ## Upgrading
 
 A playbook is provided to upgrade K3s on all nodes in the cluster. To use it, update `k3s_version` with the desired version in `inventory.yml` and run:

roles/k3s_server/defaults/main.yml

@@ -7,3 +7,4 @@ user_kubectl: true  # noqa var-naming[no-role-prefix]
 cluster_context: k3s-ansible  # noqa var-naming[no-role-prefix]
 server_group: server  # noqa var-naming[no-role-prefix]
 agent_group: agent  # noqa var-naming[no-role-prefix]
+use_external_database: false # noqa var-naming[no-role-prefix]

roles/k3s_server/tasks/main.yml

@@ -58,7 +58,7 @@
   when: inventory_hostname == groups[server_group][0]
   block:
     - name: Copy K3s service file [Single]
-      when: groups[server_group] | length == 1
+      when: groups[server_group] | length == 1 or use_external_database
       ansible.builtin.template:
         src: "k3s-single.service.j2"
         dest: "{{ systemd_dir }}/k3s.service"
@@ -67,7 +67,9 @@
         mode: "0644"
 
     - name: Copy K3s service file [HA]
-      when: groups[server_group] | length > 1
+      when:
+        - groups[server_group] | length > 1
+        - not use_external_database
       ansible.builtin.template:
         src: "k3s-cluster-init.service.j2"
         dest: "{{ systemd_dir }}/k3s.service"
@@ -148,7 +150,9 @@
     - inventory_hostname != groups[server_group][0]
   block:
     - name: Copy K3s service file [HA]
-      when: groups[server_group] | length > 1
+      when:
+        - groups[server_group] | length > 1
+        - not use_external_database
       ansible.builtin.template:
         src: "k3s-ha.service.j2"
         dest: "{{ systemd_dir }}/k3s.service"
@@ -156,6 +160,17 @@
         group: root
         mode: "0644"
 
+    - name: Copy K3s service file [External DB]
+      when:
+        - groups[server_group] | length > 1
+        - use_external_database
+      ansible.builtin.template:
+        src: "k3s-single.service.j2"
+        dest: "{{ systemd_dir }}/k3s.service"
+        owner: root
+        group: root
+        mode: "0644"
+
     - name: Enable and check K3s service
       ansible.builtin.systemd:
         name: k3s