xesite/blog/nixos-discord-webhook-2020-...

145 lines
4.0 KiB
Markdown
Raw Normal View History

---
title: Discord Webhooks via NixOS and Systemd Timers
date: 2020-11-30
series: howto
tags:
- nixos
- discord
- systemd
---
Recently I needed to set up a Discord message on a cronjob as a part of
moderating a guild I've been in for years. I've done this before using
[cronjobs](/blog/howto-automate-discord-webhook-cron-2018-03-29), however this
time we will be using [NixOS](https://nixos.org/) and [systemd
timers](https://wiki.archlinux.org/index.php/Systemd/Timers). Here's what you
will need to follow along:
- A machine running NixOS
- A [Discord](https://discord.com/) account
- A
[webhook](https://support.discord.com/hc/en-us/articles/228383668-Intro-to-Webhooks)
configured for a channel
- A message you want to send to Discord
[If you don't have moderation permissions in any guilds, make your own for
testing! You will need the "Manage Webhooks" permission to create a
webhook.](conversation://Mara/hacker)
## Setting Up Timers
systemd timers are like cronjobs, except they trigger systemd services instead
of shell commands. For this example, let's create a daily webhook reminder to
check on your Animal Crossing island at 9 am.
Let's create the systemd service at the end of the machine's
`configuration.nix`:
```nix
systemd.services.acnh-island-check-reminder = {
serviceConfig.Type = "oneshot";
script = ''
MESSAGE="It's time to check on your island! Check those stonks!"
WEBHOOK="${builtins.readFile /home/cadey/prefix/secrets/acnh-webhook-secret}"
USERNAME="Domo"
${pkgs.curl}/bin/curl \
-X POST \
-F "content=$MESSAGE" \
-F "username=$USERNAME" \
"$WEBHOOK"
'';
};
```
[This service is a <a href="https://stackoverflow.com/a/39050387">oneshot</a>
unit, meaning systemd will launch this once and not expect it to always stay
running.](conversation://Mara/hacker)
Now let's create a timer for this service. We need to do the following:
- Associate the timer with that service
- Assign a schedule to the timer
Add this to the end of your `configuration.nix`:
```nix
systemd.timers.acnh-island-check-reminder = {
wantedBy = [ "timers.target" ];
partOf = [ "acnh-island-check-reminder.service" ];
timerConfig.OnCalendar = "TODO(Xe): this";
};
```
Before we mentioned that we want to trigger this reminder every morning at 9 am.
systemd timers specify their calendar config in the following format:
```
DayOfWeek Year-Month-Day Hour:Minute:Second
```
So for something that triggers every day at 9 AM, it would look like this:
```
*-*-* 8:00:00
```
[You can ignore the day of the week if it's not
relevant!](conversation://Mara/hacker)
So our final timer definition would look like this:
```nix
systemd.timers.acnh-island-check-reminder = {
wantedBy = [ "timers.target" ];
partOf = [ "acnh-island-check-reminder.service" ];
timerConfig.OnCalendar = "*-*-* 8:00:00";
};
```
## Deployment and Testing
Now we can deploy this with `nixos-rebuild`:
```console
$ sudo nixos-rebuild switch
```
You should see a line that says something like this in the `nixos-rebuild`
output:
```
starting the following units: acnh-island-check-reminder.timer
```
Let's test the service out using `systemctl`:
```console
$ sudo systemctl start acnh-island-check-reminder.service
```
And you should then see a message on Discord. If you don't see a message, check
the logs using `journalctl`:
```console
$ journalctl -u acnh-island-check-reminder.service
```
If you see an error that looks like this:
```
curl: (26) Failed to open/read local data from file/application
```
This usually means that you tried to do a role or user mention at the beginning
of the message and curl tried to interpret that as a file input. Add a word like
"hey" at the beginning of the line to disable this behavior. See
[here](https://stackoverflow.com/questions/6408904/send-request-to-curl-with-post-data-sourced-from-a-file)
for more information.
---
Also happy December! My site has the [snow
CSS](https://xeiaso.net/blog/let-it-snow-2018-12-17) loaded for the
month. Enjoy!