retry the remaining plain schedules with backon

swarm-controller/src/read_policy.rs

@@ -29,6 +29,7 @@
 use std::{future::Future, time::Duration};
 
 use anyhow::{Context, Result};
+use backon::{BackoffBuilder as _, ConstantBuilder};
 use swarm_secret_client::{Error, SecretStore, client::DEFAULT_CERT_MOUNT, policy};
 
 /// File holding the authority hives are issued from, as
@@ -111,12 +112,14 @@ where
     F: FnMut() -> Fut,
     Fut: Future<Output = Result<(), Unreachable>>,
 {
-    let mut ticker = tokio::time::interval(interval);
-    // `interval`'s first tick is immediate, and that pass is the one the caller
-    // already ran before deciding to retry at all.
-    ticker.tick().await;
-    for n in 1..=attempts {
-        ticker.tick().await;
+    // One delay per attempt, waited before it: the pass the caller already ran
+    // before deciding to retry at all is the attempt that needs no wait.
+    let delays = ConstantBuilder::default()
+        .with_delay(interval)
+        .with_max_times(attempts as usize)
+        .build();
+    for (n, delay) in (1..).zip(delays) {
+        tokio::time::sleep(delay).await;
         if attempt().await.is_ok() {
             return Some(n);
         }