mykb/docs/anki_sync_server.md

Anki Sync Server

With the new versions of Anki, anki now provides an integrated sync-server feature, allowing for up-to-date scheduler versions as long as anki on the server is also updated regularly. Other implementations such as Anki Sync Server might be less resource intensive but need to be updated separately to allow for newer scheduler versions. This requires quite a bit of memory, but a lot if it is shared. If you run anything else using python (very likely), running this sync server in addition should maybe require an additional 100-200M.

Installation

Install anki: paru -S anki

We're assuming here that you are running the latest Anki on your server, however you manage to do that (some distros are quite conservative with their anki versions). On Arch, I currently maintain the anki and anki-qt5 packages in the AUR so they should be up-to-date.

Reverse Proxy using nginx

Anki creates a sync server locally on 0.0.0.0:8080. We want to put this behind a reverse proxy for convenience. Create a new server{} section in your nginx setup. Recommended is a new file in /etc/nginx/sites-available/anki_sync_server

server {
	server_name anki.<yourdomain.tld>;
	listen 80;
	client_max_body_size 500M;
	location / {
		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
		proxy_set_header Host $host;

		proxy_pass http://0.0.0.0:8080;

		proxy_buffering off;
		proxy_http_version 1.1;
		proxy_set_header Upgrade $http_upgrade;
		proxy_set_header Connection "upgrade";
	}
}

Some of these settings are a bit overkill for anki, but are good defaults for modern web applications behind a reverse proxy.

Link to enabled sites:

ln -s /etc/nginx/sites-available/anki_sync_server /etc/nginx/sites-enabled/

Check whether the syntax is good via nginx -t and if so, restart nginx systemctl restart nginx. This is still unencrypted. Using certbot you can now deploy certificates

certbot --nginx -d anki.<yourdomain.tld>

If everything goes good you should be able to verify in /etc/nginx/sites-available/anki_sync_server.

Create a user and service

Personally, I see this sync data as a kind of database and would like to store it in /var/lib because of this. For security we should start anki as a separate user with write permissions confined to /var/lib/anki. Create a user:

useradd -b /var/lib/ -s /usr/bin/nologin anki
mkdir /var/lib/anki
chown -R /var/lib/anki anki:anki

Using systemd, create a service file: /etc/systemd/system/anki_sync_server.service:

[Unit]
Description=Personal Anki Sync Server
After=network.target

[Service]
ExecStart=anki --syncserver
Restart=always
User=anki
Group=anki
Environment=SYNC_BASE="/var/lib/anki"
Environment=MAX_SYNC_PAYLOAD_MEGS=500
Environment=SYNC_USER1=<name1>:<password1>
Environment=SYNC_USER2=<name2>:<password2>

[Install]
WantedBy=multi-user.target

You can create additional users using the SYNC_USER<i> environment variables. This stores the passwords in plain text on the machine so is less than optimal.

TODO: can we somehow store these env vars securely?

You should now be able to start your sync server via systemctl start anki_sync_server.service. If everything looks good in the journal, you can sytemctl renable anki_sync_server.

Connecting from your Client

Desktop

1. Go to: Tools -> Preferences -> Syncing
2. Logout
3. set "Self-hosted-sync-server" to https://anki.<yourdomain.tld>
4. Restart anki
5. Click on Sync and login using your <name1> and <password1> which you set in the service file.

Ankidroid

1. Go to: Settings -> Advanced -> Custom sync server
2. Set the sync url to: https://anki.<yourdomain.tld>
3. Set the media sync url to https://anki.<yourdomain.tld>/msync
4. Click on the sync icon in the main top-bar. Login using your <name1> and <password1> you set in the service file.

More info

See https://docs.ankiweb.net/sync-server.html