Make roles more independent of one another

With this change, the following roles are now only dependent
on the minimal `matrix-base` role:
- `matrix-corporal`
- `matrix-coturn`
- `matrix-mailer`
- `matrix-mxisd`
- `matrix-postgres`
- `matrix-riot-web`
- `matrix-synapse`

The `matrix-nginx-proxy` role still does too much and remains
dependent on the others.

Wiring up the various (now-independent) roles happens
via a glue variables file (`group_vars/matrix-servers`).
It's triggered for all hosts in the `matrix-servers` group.

According to Ansible's rules of priority, we have the following
chain of inclusion/overriding now:
- role defaults (mostly empty or good for independent usage)
- playbook glue variables (`group_vars/matrix-servers`)
- inventory host variables (`inventory/host_vars/matrix.<your-domain>`)

All roles default to enabling their main component
(e.g. `matrix_mxisd_enabled: true`, `matrix_riot_web_enabled: true`).
Reasoning: if a role is included in a playbook (especially separately,
in another playbook), it should "work" by default.

Our playbook disables some of those if they are not generally useful
(e.g. `matrix_corporal_enabled: false`).

roles/matrix-corporal/tasks/init.yml

@@ -1,9 +1,3 @@
-- name: Override configuration specifying where the Matrix Client API is
-  set_fact:
-    matrix_nginx_proxy_matrix_client_api_addr_with_proxy_container: "matrix-corporal:41080"
-    matrix_nginx_proxy_matrix_client_api_addr_sans_proxy_container: "localhost:41080"
-  when: "matrix_corporal_enabled"
-
 - set_fact:
     matrix_systemd_services_list: "{{ matrix_systemd_services_list + ['matrix-corporal'] }}"
   when: "matrix_corporal_enabled"

roles/matrix-corporal/tasks/main.yml

@@ -2,6 +2,12 @@
   tags:
     - always
 
+- import_tasks: "{{ role_path }}/tasks/validate_config.yml"
+  when: "run_setup and matrix_corporal_enabled"
+  tags:
+    - setup-all
+    - setup-corporal
+
 - import_tasks: "{{ role_path }}/tasks/setup_corporal.yml"
   when: run_setup
   tags:

roles/matrix-corporal/tasks/setup_corporal.yml

@@ -4,24 +4,6 @@
 # Tasks related to setting up matrix-corporal
 #
 
-- name: Fail if Shared Secret Auth extension not enabled
-  fail:
-    msg: "To use matrix-corporal, you need to enable the Shared Secret Auth module for Synapse (see matrix_synapse_ext_password_provider_shared_secret_auth_enabled)"
-  when: "matrix_corporal_enabled and not matrix_synapse_ext_password_provider_shared_secret_auth_enabled"
-
-- name: Fail if HTTP API enabled, but no token set
-  fail:
-    msg: "The Matrix Corporal HTTP API is enabled, but no auth token has been set in matrix_corporal_http_api_auth_token"
-  when: "matrix_corporal_enabled and matrix_corporal_http_api_enabled and matrix_corporal_http_api_auth_token == ''"
-
-- name: Fail if policy provider configuration not set
-  fail:
-    msg: "The Matrix Corporal policy provider configuration has not been set in matrix_corporal_policy_provider_config"
-  when: "matrix_corporal_enabled and matrix_corporal_policy_provider_config == ''"
-
-# There are some additional initialization tasks in setup_corporal_overrides.yml,
-# which need to always run, no matter what tag the playbook is running with.
-
 - name: Ensure Matrix Corporal paths exist
   file:
     path: "{{ item }}"

roles/matrix-corporal/tasks/validate_config.yml

@@ -0,0 +1,17 @@
+---
+
+- name: Fail if required matrix-corporal settings not defined
+  fail:
+    msg: >
+      You need to define a required configuration setting (`{{ item }}`) for using matrix-corporal.
+  when: "vars[item] == ''"
+  with_items:
+    - "matrix_corporal_matrix_homeserver_api_endpoint"
+    - "matrix_corporal_matrix_auth_shared_secret"
+    - "matrix_corporal_matrix_registration_shared_secret"
+    - "matrix_corporal_policy_provider_config"
+
+- name: Fail if HTTP API enabled, but no token set
+  fail:
+    msg: "The Matrix Corporal HTTP API is enabled (`matrix_corporal_http_api_enabled`), but no auth token has been set in `matrix_corporal_http_api_auth_token`"
+  when: "matrix_corporal_http_api_enabled and matrix_corporal_http_api_auth_token == ''"