# Nextcloud Cron Job Docker Container

## 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. Note for this example,
the `docker-compose.yml` file is located at `~/docker_services/nextcloud/docker-compose.yml`.

```yml
version: '3.7'

services:
  app:
    image: nextcloud:apache

  cron:
    image: rcdailey/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. In this case, my project name is
`nextcloud` because Docker Compose uses the name of the directory containing the
`docker-compose.yml` file to prefix the name of the image. And container name is `app` because
that's what I named the service in the YAML file.

Note that if you don't use Docker Compose, you can leave `NEXTCLOUD_PROJECT_NAME` blank or omitted
entirely. Please see the Environment Variables section below for more details on configuration and
how this all works.

## 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:

  ```txt
  ${NEXTCLOUD_PROJECT_NAME}_${NEXTCLOUD_CONTAINER_NAME}
  ```

* `NEXTCLOUD_CRON_MINUTE_INTERVAL`<br>
  The interval, in minutes, of how often the cron task executes. The default is 15 minutes.

* `NEXTCLOUD_EXEC_USER`<br>
  The user that should be used to run the cron tasks inside the Nextcloud container. This parameter
  is specified to the `docker exec` command from this container. By default, the user used is
  `www-data`, which is also the default user used inside Nextcloud, unless you've overridden it. You
  may also define this environment variable to be blank (e.g. `NEXTCLOUD_EXEC_USER=`) which results
  in the tasks being executed using the Nextcloud container's running user. Specifically, the
  `--user` option will *not* be provided to the `docker exec` command.

* `NEXTCLOUD_EXEC_SHELL`<br>
  Allows specifying a custom shell program that will be used to execute cron tasks inside the
  Nextcloud container. This shell program *must* exist inside the Nextcloud container itself
  (validation happens on start up to ensure this). The default value if not specified is `bash`.

* `NEXTCLOUD_EXEC_SHELL_ARGS`<br>
  Allows custom arguments to be passed to the shell program specified by `NEXTCLOUD_EXEC_SHELL`. See
  the detailed documentation provided later on in this document for more information. At minimum,
  the arguments passed to your shell program must allow for the execution of a series of string
  commands. The default value if not specified is `-c`.

* `DEBUG`<br>
  Enables more verbose logging in core scripts. Useful only for development. To get more verbose
  output in your own custom cron scripts, use `set -x` in the actual script.

## 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.

Because the Nextcloud container can be restarted while the the cronjob container is running, its
container ID is not cached. Each time the cron task executes, it searches for the ID of the
container. This ensures that even if you restart the Nextcloud container, the cronjob container will
always function.

## Customizing Cron Tasks

This container provides the ability for you to run additional tasks inside the Nextcloud container
in addition to the default `cron.php` task. To add your custom tasks, follow these steps:

1. Write a shell script that runs the commands that will be part of your task. This shell script
   must have the `.sh` extension. An example of the contents of such a script is below. As an
   optional security measure, do not make this shell script executable. The contents of the file are
   piped into `sh`, so the executable bit and shebang line are not used or required.

   ```sh
   php -f /var/www/html/cron.php
   ```

2. Mount this shell script inside the `/cron-scripts` directory. You may also choose to *replace*
   this directory, but bear in mind that you will not be running the built-in cron tasks in that
   case. Here's an example if you're using `docker-compose.yml`:

   ```yml
   services:
     cron:
       image: rcdailey/nextcloud-cronjob
       volumes:
       - ./my-scripts/do-something.sh:/cron-scripts/do-something.sh:ro
   ```

3. Recreate the container. Your script will now execute in the Nextcloud container at a regular
   interval.

Multiple scripts are supported. The container will search for all `*.sh` files inside the
`/cron-scripts` directory. To make supporting multiple scripts easier, you can also map a directory
on the host to the `/cron-scripts` directory in the container:

```yml
services:
  cron:
    image: rcdailey/nextcloud-cronjob
    volumes:
    - ./my-scripts:/cron-scripts:ro
```

As an optional safety measure, mount the directory or files as read-only (via the `:ro` at the end).
The container should not modify the files, but it doesn't hurt to be explicitly strict.

### Customizing the Shell

By default, all cron task scripts in the `/cron-scripts` directory are executed with `bash`.
However, not all Nextcloud containers have `bash`. In this case, you may want to override it with a
shell like `sh`. You can accomplish this (as well as customizing the arguments passed to the shell)
with `NEXTCLOUD_EXEC_SHELL` and `NEXTCLOUD_EXEC_SHELL_ARGS`.

The shell args are used when passing the contents of script files to the shell executable inside the
Nextcloud container. Customizing the args might be necessary depending on the shell program you
choose, or you may want to leverage options for debugging purposes (See "Debugging" section for
examples).

> **NOTE**<br>
> The arguments that are passed to the shell program must, at least, allow the execution of a string
> of commands. See the documentation on your chosen shell for which arguments these should be.

Here is an example of how you would override `bash` for `sh` using `docker-compose.yml` (again,
greatly simplified for example purposes; this is not a complete YAML):

```yml
services:
  cron:
    image: rcdailey/nextcloud-cronjob
    environment:
    - NEXTCLOUD_EXEC_SHELL=sh
    - NEXTCLOUD_EXEC_SHELL_ARGS=-c
```

Note that `-c` is the default for `NEXTCLOUD_EXEC_SHELL_ARGS`, so it isn't necessary to specify it
above. However, it is explicitly specified for example purposes.

### Notes

* All cron task shell scripts run at the same interval defined by `NEXTCLOUD_CRON_MINUTE_INTERVAL`.
* Modification of your own shell scripts on the host do not require that you restart/recreate the
  container (only when volume mappings change in the YAML file).

## 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. Here is
an example of the logs you will see:

```txt
Started crond
-------------------------------------------------------------
 Executing Cron Tasks: Thu Dec  6 17:28:00 CST 2018
-------------------------------------------------------------
> Running Script: occ-preview-pre-generate.sh
> Running Script: run_cron_php.sh
> Done
```

You can leverage `NEXTCLOUD_EXEC_SHELL_ARGS` to get more verbose output from your scripts. For
example, for `bash` you can specify `-x` for debug mode. So you could use this in your YAML:

```yml
services:
  cron:
    image: rcdailey/nextcloud-cronjob
    environment:
    - NEXTCLOUD_EXEC_SHELL_ARGS=-xc
```

Note the addition of `-x` in the arguments. This will provide line-by-line output for each cron task
shell script executed.