Document repeat option

Readme.md

@@ -10,8 +10,8 @@ this creates a dynamic DNS system.
 If you want to host web services but you don't have a static IP address, this
 tool will allow you to keep your domains pointed at the right IP address. This
 program can update both IPv4 and IPv6 addresses for one or more domains and
-subdomains. It's a one-shot tool that's meant to be managed with a systemd timer
-or cron.
+subdomains. It can be used as a one-shot tool managed with a systemd timer
+or cron, or a long-running process that reschedules itself.
 
 ## Usage
 
@@ -67,6 +67,34 @@ build it from source and you have a working rust install, you can use `cargo ins
 
 ## Automation
 
+### By running as a background process
+
+`gandi-live-dns` can run as a daemon, a background process, periodically perform
+the IP address updates. To do so, add the `--repeat=<delay-in-seconds>` command
+line option. When given, this tool will not quit after updating your IP address
+and instead will continue to perform periodic updates.
+
+If you are using Docker, you can add this option when starting it:
+
+```bash
+# This will update your IP now, then repeat every 24 hours
+docker run --rm -it -v $(pwd)/gandi.toml:/gandi.toml:ro seriousbug/gandi-live-dns-rust:latest --repeat=86400
+```
+
+Or with a `docker-compose.yml` file, add it in the arguments:
+
+```yml
+  gandi-live-dns:
+    image: seriousbug/gandi-live-dns-rust:latest
+    restart: always
+    volumes:
+      - ./gandi.toml:/gandi.toml:ro
+    # Repeat the update every day
+    command: --repeat=86400
+```
+
+### With a Systemd timer
+
 The `Packaging` folder contains a Systemd service and timer, which you can use
 to automatically run this tool. By default it will update the IP addresses after
 every boot up, and at least once a day. You can adjust the timer to speed this

src/opts.rs

@@ -17,9 +17,14 @@ pub struct Opts {
     /// If enabled, any IPv6 (AAAA) records in the configuration file are ignored.
     #[clap(action, long)]
     pub skip_ipv6: bool,
-    /// Repeat after specified delay
+    /// Repeat after specified delay, in seconds.
     ///
-    /// If enabled waits for the given delay between updating DNS records
+    /// If enabled, this will continue to run and perform the updates
+    /// periodically. The first update will happen immediately, and later
+    /// updates will be delayed by this many seconds.
+    ///
+    /// This process will not fork, so you may need to use something like
+    /// `nohup` to keep it running in the background.
     #[clap(long)]
     pub repeat: Option<u64>,
 }