fix: add proportional jitter to reduce synchronized API calls

Cargo.lock

@@ -84,6 +84,7 @@ name = "cloudflare-ddns"
 version = "2.1.0"
 dependencies = [
  "if-addrs",
+ "rand",
  "regex-lite",
  "reqwest",
  "rustls",
@@ -298,6 +299,18 @@ dependencies = [
  "wasi",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 5.3.0",
+ "wasip2",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.2"
@@ -306,7 +319,7 @@ checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
 dependencies = [
  "cfg-if",
  "libc",
- "r-efi",
+ "r-efi 6.0.0",
  "wasip2",
  "wasip3",
 ]
@@ -772,6 +785,15 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85eae3c4ed2f50dcfe72643da4befc30deadb458a9b590d720cde2f2b1e97da9"
+dependencies = [
+ "zerocopy",
+]
+
 [[package]]
 name = "prettyplease"
 version = "0.2.37"
@@ -800,12 +822,47 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "5.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
 [[package]]
 name = "r-efi"
 version = "6.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
 
+[[package]]
+name = "rand"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6db2770f06117d490610c7488547d543617b21bfa07796d7a12f6f1bd53850d1"
+dependencies = [
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76afc826de14238e6e8c374ddcc1fa19e374fd8dd986b0d2af0d02377261d83c"
+dependencies = [
+ "getrandom 0.3.4",
+]
+
 [[package]]
 name = "regex"
 version = "1.12.3"
@@ -1830,6 +1887,26 @@ dependencies = [
  "synstructure",
 ]
 
+[[package]]
+name = "zerocopy"
+version = "0.8.48"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eed437bf9d6692032087e337407a86f04cd8d6a16a37199ed57949d415bd68e9"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.8.48"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70e3cd084b1788766f53af483dd21f93881ff30d7320490ec3ef7526d203bad4"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "zerofrom"
 version = "0.1.6"

Cargo.toml

@@ -14,6 +14,7 @@ tokio = { version = "1", features = ["rt", "macros", "time", "signal", "net"] }
 regex-lite = "0.1"
 url = "2"
 if-addrs = "0.15"
+rand = "0.9"
 
 [profile.release]
 opt-level = "z"

src/main.rs

@@ -14,6 +14,7 @@ use crate::pp::PP;
 use std::collections::HashSet;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
+use rand::Rng;
 use reqwest::Client;
 use tokio::signal;
 use tokio::time::{sleep, Duration};
@@ -251,12 +252,28 @@ async fn run_env_mode(
                     return;
                 }
 
+                // Apply proportional jitter before each update to spread API calls
+                // across clients and reduce synchronized traffic spikes at Cloudflare.
+                let max_jitter = interval.as_secs() / 5;
+                if max_jitter > 0 {
+                    let jitter_secs = rand::rng().random_range(0..=max_jitter);
+                    sleep(std::time::Duration::from_secs(jitter_secs)).await;
+                }
+
                 updater::update_once(config, handle, notifier, heartbeat, cf_cache, ppfmt, &mut noop_reported, detection_client).await;
             }
         }
     }
 }
 
+fn jitter_duration(interval_secs: u64, rand_val: u64) -> std::time::Duration {
+    let max_jitter = interval_secs / 5;
+    if max_jitter == 0 {
+        return std::time::Duration::ZERO;
+    }
+    std::time::Duration::from_secs(rand_val % (max_jitter + 1))
+}
+
 fn describe_duration(d: Duration) -> String {
     let secs = d.as_secs();
     if secs >= 3600 {
@@ -866,6 +883,29 @@ mod tests {
             .await;
     }
 
+    // --- jitter_duration tests ---
+    #[test]
+    fn test_jitter_duration_standard() {
+        // 5-minute interval: max jitter = 60s
+        let d = super::jitter_duration(300, 30);
+        assert_eq!(d, std::time::Duration::from_secs(30));
+        let d = super::jitter_duration(300, 61);
+        assert_eq!(d, std::time::Duration::from_secs(61 % 61)); // wraps within [0, 60]
+    }
+
+    #[test]
+    fn test_jitter_duration_short_interval() {
+        // interval < 5s: must return zero
+        assert_eq!(super::jitter_duration(4, 99), std::time::Duration::ZERO);
+        assert_eq!(super::jitter_duration(0, 99), std::time::Duration::ZERO);
+    }
+
+    #[test]
+    fn test_jitter_duration_deterministic() {
+        // rand_val=0 always returns zero duration
+        assert_eq!(super::jitter_duration(300, 0), std::time::Duration::ZERO);
+    }
+
     // --- describe_duration tests ---
     #[test]
     fn test_describe_duration_seconds_only() {