Problem: a) Protonmail Bridge cannot listen to IP other than 127.0.0.1, and b) Discourse in a Docker container cannot send SMTP requests to 127.0.0.1 of the host machine.
Solution: We configure it to send to 172.17.0.1 (the Docker’s bridge IP on the host machine), and then redirect to 127.0.0.1, on which the Protonmail Bridge is listening.
We do it with using Socat.
How To
Start by installing Socat:
apt install socat
We will run Socat as a service. Create service file:
nano /etc/systemd/system/protonsocat.service
… and put the following content in it:
[Unit]
Description=Socat Bridge ProtonMail/Discourse
After=protonbridge.service,docker.service
ReloadPropagatedFrom=docker.service
[Service]
ExecStart=socat -d -d -lm TCP4-LISTEN:1026,fork,reuseaddr,so-bindtodevice=docker0,range=172.17.0.0/24 TCP4:127.0.0.1:1025
Restart=always
RestartSec=2
[Install]
WantedBy=multi-user.target
Notes:
-
We configured Socat to listen to all IPs
172.17.0.0/24, port1026, and redirect the traffic to127.0.0.1:1025, where Protonmail Bridge is listening -
Example from Socat documentation: <strong>socat</strong>
-
-d -d will print the fatal, error, warning, and notice messages; you may not want that much detail logged
Next, start the service:
systemctl start protonsocat
Check that it is running:
systemctl status protonsocat
And automatically get it to start on boot:
systemctl enable protonsocat
Done! Now, configure Discourse app.yml and rebuild:
DISCOURSE_SMTP_ADDRESS: 172.17.0.1
DISCOURSE_SMTP_PORT: 1026
DISCOURSE_SMTP_USER_NAME: <SMTP username supplied by the Proton Bridge command-line application>
DISCOURSE_SMTP_PASSWORD: "<SMTP password - put in quotes>"
DISCOURSE_SMTP_ENABLE_START_TLS: true
DISCOURSE_SMTP_DOMAIN: <the domain name>
DISCOURSE_NOTIFICATION_EMAIL: <here, put the address form which Discourse will send transactional emails>