feat(util-waiter): add jitter to waiters exponential backoff

aws · Dec 7, 2020 · 88ac270 · 88ac270
1 parent 2b52619
commit 88ac270
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Showing 3 changed files with 20 additions and 16 deletions.
diff --git a/packages/util-waiter/package.json b/packages/util-waiter/package.json
@@ -4,7 +4,7 @@
   "description": "Shared utilities for client waiters for the AWS SDK",
   "dependencies": {
     "tslib": "^1.8.0",
-    "@aws-sdk/abort-controller": "1.0.0-rc.7"
+    "@aws-sdk/abort-controller": "1.0.0-rc.8"
   },
   "devDependencies": {
     "@types/jest": "^26.0.4",

diff --git a/packages/util-waiter/src/poller.spec.ts b/packages/util-waiter/src/poller.spec.ts
@@ -26,10 +26,12 @@ describe(runPolling.name, () => {
 
   beforeEach(() => {
     (sleep as jest.Mock).mockResolvedValueOnce("");
+    jest.spyOn(global.Math, "random").mockReturnValue(0.5);
   });
 
   afterEach(() => {
     jest.clearAllMocks();
+    jest.spyOn(global.Math, "random").mockRestore();
   });
 
   it("should returns state in case of failure", async () => {
@@ -80,12 +82,12 @@ describe(runPolling.name, () => {
 
     expect(sleep).toHaveBeenCalled();
     expect(sleep).toHaveBeenCalledTimes(7);
-    expect(sleep).toHaveBeenNthCalledWith(1, 2);
-    expect(sleep).toHaveBeenNthCalledWith(2, 4);
-    expect(sleep).toHaveBeenNthCalledWith(3, 8);
-    expect(sleep).toHaveBeenNthCalledWith(4, 16);
-    expect(sleep).toHaveBeenNthCalledWith(5, 30);
-    expect(sleep).toHaveBeenNthCalledWith(6, 30);
-    expect(sleep).toHaveBeenNthCalledWith(7, 30);
+    expect(sleep).toHaveBeenNthCalledWith(1, 2); // min delay
+    expect(sleep).toHaveBeenNthCalledWith(2, 3); // +random() * 2
+    expect(sleep).toHaveBeenNthCalledWith(3, 5); // +random() * 4
+    expect(sleep).toHaveBeenNthCalledWith(4, 9); // +random() * 8
+    expect(sleep).toHaveBeenNthCalledWith(5, 17); // +random() * 16
+    expect(sleep).toHaveBeenNthCalledWith(6, 30); // max delay
+    expect(sleep).toHaveBeenNthCalledWith(7, 30); // max delay
   });
 });
diff --git a/packages/util-waiter/src/poller.ts b/packages/util-waiter/src/poller.ts
@@ -1,9 +1,14 @@
 import { sleep } from "./utils/sleep";
 import { WaiterOptions, WaiterResult, WaiterState } from "./waiter";
 
-function exponentialBackoff(floor: number, ciel: number, attempt: number): number {
-  return Math.min(ciel, floor * 2 ** attempt);
-}
+/**
+ * Reference: https://github.com/awslabs/smithy/pull/656
+ * The theoretical limit to the attempt is max delay cannot be > Number.MAX_VALUE, but it's unlikely because of
+ * `maxWaitTime`
+ */
+const exponentialBackoff = (floor: number, ciel: number, attempt: number) =>
+  Math.floor(Math.min(ciel, randomInRange(floor, floor * 2 ** (attempt - 1))));
+const randomInRange = (min: number, max: number) => min + Math.random() * (max - min);
 
 /**
  * Function that runs indefinite polling as part of waiters.
@@ -13,22 +18,19 @@ function exponentialBackoff(floor: number, ciel: number, attempt: number): numbe
  * @param stateChecker function that checks the acceptor states on each poll.
  */
 export const runPolling = async <T, S>(
-  params: WaiterOptions,
+  { minDelay, maxDelay }: WaiterOptions,
   client: T,
   input: S,
   acceptorChecks: (client: T, input: S) => Promise<WaiterResult>
 ): Promise<WaiterResult> => {
   let currentAttempt = 1;
-  let currentDelay = params.minDelay;
 
   while (true) {
-    await sleep(currentDelay);
+    await sleep(exponentialBackoff(minDelay, maxDelay, currentAttempt));
     const { state } = await acceptorChecks(client, input);
     if (state === WaiterState.SUCCESS || state === WaiterState.FAILURE) {
       return { state };
     }
-
-    currentDelay = exponentialBackoff(params.minDelay, params.maxDelay, currentAttempt);
     currentAttempt += 1;
   }
 };