Switch to using an external Etherpad role

This new role also adds native Traefik support and support for other
(non-`amd64`) architectures via self-building.

roles/custom/etherpad-proxy-connect/tasks/inject_into_nginx_proxy.yml

@@ -0,0 +1,46 @@
+---
+
+- name: Fail if matrix-nginx-proxy role already executed
+  ansible.builtin.fail:
+    msg: >-
+      Trying to append Etherpad's reverse-proxying configuration to matrix-nginx-proxy,
+      but it's pointless since the matrix-nginx-proxy role had already executed.
+      To fix this, please change the order of roles in your playbook,
+      so that the matrix-nginx-proxy role would run after the matrix-etherpad role.
+  when: matrix_nginx_proxy_role_executed | default(False) | bool
+
+- name: Generate Etherpad proxying configuration for matrix-nginx-proxy
+  ansible.builtin.set_fact:
+    etherpad_matrix_nginx_proxy_configuration: |
+      rewrite ^{{ etherpad_nginx_proxy_dimension_integration_path_prefix }}$ {{ matrix_nginx_proxy_x_forwarded_proto_value }}://$server_name{{ etherpad_nginx_proxy_dimension_integration_path_prefix }}/ permanent;
+
+      location {{ etherpad_nginx_proxy_dimension_integration_path_prefix }}/ {
+      {% if matrix_nginx_proxy_enabled | default(False) %}
+        {# Use the embedded DNS resolver in Docker containers to discover the service #}
+        resolver 127.0.0.11 valid=5s;
+        proxy_pass http://{{ etherpad_identifier }}:9001/;
+        {# These are proxy directives needed specifically by Etherpad #}
+        proxy_buffering off;
+        proxy_http_version 1.1;  # recommended with keepalive connections
+        proxy_pass_header Server;
+        proxy_set_header Host $host;
+        proxy_set_header X-Forwarded-Proto {{ matrix_nginx_proxy_x_forwarded_proto_value }}; # for EP to set secure cookie flag when https is used
+        # WebSocket proxying - from http://nginx.org/en/docs/http/websocket.html
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection $connection_upgrade;
+      {% else %}
+        {# Generic configuration for use outside of our container setup #}
+        # A good guide for setting up your Etherpad behind nginx:
+        # https://docs.gandi.net/en/cloud/tutorials/etherpad_lite.html
+        proxy_pass http://127.0.0.1:9001/;
+      {% endif %}
+      }
+
+- name: Register Etherpad proxying configuration with matrix-nginx-proxy
+  ansible.builtin.set_fact:
+    matrix_nginx_proxy_proxy_dimension_additional_server_configuration_blocks: |
+      {{
+        matrix_nginx_proxy_proxy_dimension_additional_server_configuration_blocks | default([])
+        +
+        [etherpad_matrix_nginx_proxy_configuration]
+      }}