I thought I would follow up on the Fail2Ban Pushover post with a Fail2Ban Discord post!

Creating the Webhook

In this guide you will be using a Discord webhook to post Fail2Ban notifications to the server of your choice. If you don’t have a discord server yet you need to create one.
Head over to the Server Settings and select Webhooks. Click on Create Webhook and add the name and channel you want the webhook to post to.
At the bottom you will find the webhook url, save that for later.

Adding the Discord action

Head over to your Fail2Ban action.d folder and create a file called discord_notifications.conf and add the following:

# Author: Gilbn from https://technicalramblings.com
# Adapted Source: https://gist.github.com/sander1/075736a42db2c66bc6ce0fab159ca683
# Create the Discord Webhook in: Server settings -> Webhooks -> Create Webhooks

[Definition]

# Notify on Startup
actionstart = curl -X POST "<webhook>" \
            -H "Content-Type: application/json" \
            -d '{"username": "Fail2Ban", "content":":white_check_mark: The **[<name>]** jail has started"}'

# Notify on Shutdown
actionstop = curl -X POST "<webhook>" \
            -H "Content-Type: application/json" \
            -d '{"username": "Fail2Ban", "content":":no_entry: The **[<name>]** jail has been stopped"}'
            
#
actioncheck =

# Notify on Banned 
actionban = curl -X POST "<webhook>" \
            -H "Content-Type: application/json"  \
            -d '{"username":"Fail2Ban", "content":":bell: Hey <discord_userid>! **[<name>]** :hammer:**BANNED**:hammer: IP: `<ip>` for <bantime> hours after **<failures>** failure(s). Here is some info about the IP: https://db-ip.com/<ip>"}' 
            curl -X POST "<webhook>" \
            -H "Content-Type: application/json"  \
            -d '{"username":"Fail2Ban", "content":"If you want to unban the IP run: `fail2ban-client unban <ip>`"}'

# Notify on Unbanned
actionunban = curl -X POST "<webhook>" \
            -H "Content-Type: application/json" \
            -d '{"username":"Fail2Ban", "content":":bell: **[<name>]** **UNBANNED** IP: [<ip>](https://db-ip.com/<ip>)"}'
[Init]

# Name of the jail in your jail.local file. default = [your-jail-name]
name = default

# Discord Webhook URL
webhook = https://discordapp.com/api/webhooks/XXXXXXXXXXXXXXX/XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Replace the webhook URL with the one from your webhook

If you dont want it to notify you on startup/shutdown/unban you can just comment that line with a #.

Like so:

#actionstart = curl -X POST "<webhook>" \
#            -H "Content-Type: application/json" \
#            -d '{"username": "Fail2Ban", "content":":white_check_mark: The **[<name>]** jail has started"}'

Updating jail.local

Next edit you jail.local file and add the action. You will have to add to all the jails you want notifications on or you can add it below the [DEFAULT] line .
Since I use Cloudflare and already have an action in all my jails, I’ve added it on the line below. If you don’t have another action there already you can just add the line action = discord_notifications

Example:
[nginx-http-auth]

enabled  = true
filter   = nginx-http-auth
action   = cloudflare-apiv4
           discord_notifications[bantime=24, discord_userid=<@!xxxxxxxxxxxxxxxxxxxx>]
port     = http,https
logpath  = /config/log/nginx/error.log
ignoreip = 192.168.1.0/24

Note: The [bantime=24] is just a tag that the action uses. It does not control how long the ban lasts. I default all bans to 24 hours.
Note2: The discord_userid=<@!USER-ID-NUMBER> is for mentioning yourself in the server so you can get a ping.  To find your user ID-number just type \@<username> or \@<role>, like so \@GilbN#1337 
Don’t forget the ! after @ when adding it to the action tag in the jail.
The result should look like this:

If you want to ping a role you need to edit the tag to say <@&ROLE-ID-NUMBER> instead.

Note3: The ignore IP is so that fail2ban won’t ban your local IP.
Check out https://www.aelius.com/njh/subnet_sheet.html if you are wondering what your CIDR notation is. Most often it will be /24 (netmask 255.255.255.0)
To find your netmask run ipconfig /all on windows or ifconfig | grep netmask on linux.

After you have added the action to all your jails you need to restart fail2ban. For me that will be to restart the letsencrypt container as I’m using Docker.

Discord

The notifications will look like this:
You can change the text by editing the discord_notifications.conf file