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README.md

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+# Summary
+
+This container is designed to run along side your Nextcloud container to execute its
+`/var/www/html/cron.php` at a regular interval. There is an "official" way of doing this, however it
+doesn't work when you run your Nextcloud container using a non-root user. I also personally feel
+that this solution is easier to manage, since it doesn't require the same environment as Nextcloud
+itself (i.e. no network requirements, no database requirements, etc).
+
+# Setup Instructions
+
+Since Nextcloud's entire setup can get rather complex with Docker, I highly recommend you set up
+everything using [Docker Compose](https://docs.docker.com/compose/).
+
+Below is an example of how you set up your `docker-compose.yml` to work with Nextcloud using this
+container. Note that the `app` service is greatly simplified for example purposes. It is only to
+show usage of the cronjob image in conjunction with your Nextcloud container.
+
+```yml
+version: '3.7'
+
+services:
+  app:
+    image: nextcloud:apache
+
+  cron:
+    image: voidpointer/nextcloud-cronjob
+    restart: always
+    network_mode: none
+    depends_on:
+      - app
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+      - /etc/localtime:/etc/localtime:ro
+    environment:
+      - NEXTCLOUD_CONTAINER_NAME=app
+      - NEXTCLOUD_PROJECT_NAME=nextcloud
+```
+
+In this example, the `cron` service runs with a dependency on `app` (which is Nextcloud itself).
+Every 15 minutes (default) the `cron` service will execute `php -f /var/www/html/cron.php` via the
+`docker exec` command. The `NEXTCLOUD_CONTAINER_NAME` and `NEXTCLOUD_PROJECT_NAME` work together to
+help identify the right container to execute the command in.
+
+Note that if you don't use Docker Compose, you can leave `NEXTCLOUD_PROJECT_NAME` blank or omitted
+entirely.
+
+# Environment Variables
+
+* `NEXTCLOUD_CONTAINER_NAME`<br>
+  Required. This is the name of the running Nextcloud container (or
+  the service, if `NEXTCLOUD_PROJECT_NAME` is specified).
+* `NEXTCLOUD_PROJECT_NAME`<br>
+  The name of the project if you're using Docker Compose. The name of
+  the project, by default, is the name of the context directory you ran your `docker-compose.yml`
+  from. This helps to build a "hint" used to identify the Nextcloud container by name. The hint is
+  built as:
+
+      ${NEXTCLOUD_PROJECT_NAME}_${NEXTCLOUD_CONTAINER_NAME}
+* `NEXTCLOUD_CRON_MINUTE_INTERVAL`<br>
+  The interval, in minutes, of how often the cron task
+  executes. The default is 15 minutes.
+
+# Container Health
+
+If you do `docker-compose ps`, you will see the active health of the container. The following logic
+is checked every interval of the health check. If any of these checks fail, it is likely the
+container's health status will become *unhealthy*. In this case, you should restart the container.
+
+1. The `crond` process must be running.
+2. The Nextcloud container must be available and running. One important note here: When this
+   container starts up, it immediately searches for the container by name and remembers it by the
+   container's ID. If for whatever reason the Nextcloud container changes in such a way that the ID
+   is no longer valid, the health check would fail.
+
+# Debugging
+
+All logs from `crond` are configured to print to stdout, so you can monitor container logs (via
+`docker-compose logs -f`). This should allow you to make sure your cron job is working. You can also
+use the "Overview" page in Nextcloud Settings to see if the cron job is being run regularly.