with-retry-exponential-backoff

(defn with-retry
  "Calls f until it succeeds, retrying with capped exponential backoff and jitter."
  [f {:keys [attempts base-ms max-ms] :or {attempts 5 base-ms 100 max-ms 5000}}]
  (loop [n 0]
    (let [result (try {:ok (f)} (catch Exception e {:err e}))]
      (if (:ok result)
        (:ok result)
        (if (>= n (dec attempts))
          (throw (:err result))
          (let [cap   (min max-ms (* base-ms (bit-shift-left 1 n)))
                pause (+ (quot cap 2) (rand-int (inc cap)))]
            (Thread/sleep pause)
            (recur (inc n))))))))