Add caddy README

roles/caddy/README.md

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+# Caddy 
+
+Caddy is the reverse proxy for all other services running on the infrastructure.
+It was chosen for its relative ease of use, 
+interactible API and https-by-default setup.
+
+## Variables
+
+```
+caddy_caddyfile_dir: "{{ docker_stack_files_dir }}/caddy"
+```
+
+Sets up the on-target directory where important caddy files should be stored.
+
+```
+caddy_email: <your@email.here>
+```
+
+Which e-mail should be used to provision https certificates with. I believe theoretically caddy will work and provision you with certificates even without providing an e-mail, but I would strongly urge providing one.
+
+```
+caddy_tls_use_staging: no
+```
+
+If turned on will use the staging servers of the acme certificate service, which is useful for testing and playing around with https (due to higher API limits and less severe restrictions).
+
+```
+caddy_use_api: yes
+```
+
+If turned off, will turn off the admin api for caddy. Should only be used if no other services are intended to be provisioned on the target, since most other service stacks rely on the API to set up their proxy targets.
+
+```
+caddy_use_debug: no
+```
+
+If true, will turn on caddy's debug logging.
+
+```
+caddy_use_https: yes
+```
+
+If turned off will turn of all auto-provisioning of https certificates by caddy.
+
+```
+caddy_version: alpine
+```
+
+Sets the docker image version to be used.
+
+
+## Internal variables
+
+```yaml
+caddy_stack:
+    name: caddy
+    compose: "{{ lookup('template', 'docker-stack.yml.j2') | from_yaml }}"
+```
+
+Defines the actual docker stack which will later run on the target. 
+The name can be changed and will be used as a proxy target (`caddy.mydomain.com` or `192.168.1.1/caddy`) --- 
+though to be clear there is no intention currently to expose the caddy to the web at the moment.\
+The compose option defines which template to use for the `docker-stack.yml` file. You can either change options for the stack in the template file, 
+or directly here like the following:
+
+```yaml
+    compose: 
+      - "{{ lookup('template', 'docker-stack.yml.j2') | from_yaml }}"
+      - version: '3'
+        services:
+          another-container:
+            image: nginx:latest
+#           ...
+```
+
+```yaml
+caddy_http_server_name: http
+```
+
+```yaml
+caddy_https_server_name: https
+```
+
+The internal representation of the http and https servers respectively.