On KV 404, re-insert with 60s TTL to avoid long 404 cache HITs (cloud…

…flare#7768)
MichaelDeBoey · Jan 15, 2025 · 97603f0 · 97603f0
1 parent 19228e5
commit 97603f0
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diff --git a/.changeset/lovely-years-wash.md b/.changeset/lovely-years-wash.md
@@ -0,0 +1,5 @@
+---
+"@cloudflare/workers-shared": patch
+---
+
+fix: on a 404 from KV, we do not want the asset to stay in cache for the normal 1 year TTL. Instead we want to re-insert with a 60s TTL to revalidate and prevent a bad 404 from persisting.
diff --git a/packages/workers-shared/asset-worker/src/index.ts b/packages/workers-shared/asset-worker/src/index.ts
@@ -14,6 +14,7 @@ import type {
 	UnsafePerformanceTimer,
 } from "../../utils/types";
 import type { ColoMetadata, Environment, ReadyAnalytics } from "./types";
+import type { Toucan } from "toucan-js";
 
 export type Env = {
 	/*
@@ -100,7 +101,7 @@ export default class extends WorkerEntrypoint<Env> {
 				});
 			}
 
-			return await this.env.JAEGER.enterSpan("handleRequest", async (span) => {
+			return this.env.JAEGER.enterSpan("handleRequest", async (span) => {
 				span.setTags({
 					hostname: url.hostname,
 					eyeballPath: url.pathname,
@@ -114,8 +115,22 @@ export default class extends WorkerEntrypoint<Env> {
 					this.unstable_exists.bind(this),
 					this.unstable_getByETag.bind(this)
 				);
-			});
+			}).catch((err) =>
+				this.handleError(sentry, analytics, performance, startTimeMs, err)
+			);
 		} catch (err) {
+			return this.handleError(sentry, analytics, performance, startTimeMs, err);
+		}
+	}
+
+	handleError(
+		sentry: Toucan | undefined,
+		analytics: Analytics,
+		performance: PerformanceTimer,
+		startTimeMs: number,
+		err: unknown
+	) {
+		try {
 			const response = new InternalServerErrorResponse(err as Error);
 
 			// Log to Sentry if we can

diff --git a/packages/workers-shared/asset-worker/src/utils/kv.ts b/packages/workers-shared/asset-worker/src/utils/kv.ts
@@ -1,20 +1,46 @@
+import type { Toucan } from "toucan-js";
+
 export type AssetMetadata = {
 	contentType: string;
 };
 
 export async function getAssetWithMetadataFromKV(
 	assetsKVNamespace: KVNamespace,
 	assetKey: string,
+	sentry?: Toucan,
 	retries = 1
 ) {
 	let attempts = 0;
 
 	while (attempts <= retries) {
 		try {
-			return await assetsKVNamespace.getWithMetadata<AssetMetadata>(assetKey, {
-				type: "stream",
-				cacheTtl: 31536000, // 1 year
-			});
+			const asset = await assetsKVNamespace.getWithMetadata<AssetMetadata>(
+				assetKey,
+				{
+					type: "stream",
+					cacheTtl: 31536000, // 1 year
+				}
+			);
+
+			if (asset.value === null) {
+				// Don't cache a 404 for a year by re-requesting with a minimum cacheTtl
+				const retriedAsset =
+					await assetsKVNamespace.getWithMetadata<AssetMetadata>(assetKey, {
+						type: "stream",
+						cacheTtl: 60, // Minimum value allowed
+					});
+
+				if (retriedAsset.value !== null && sentry) {
+					sentry.captureException(
+						new Error(
+							`Initial request for asset ${assetKey} failed, but subsequent request succeeded.`
+						)
+					);
+				}
+
+				return retriedAsset;
+			}
+			return asset;
 		} catch (err) {
 			if (attempts >= retries) {
 				throw new Error(

diff --git a/packages/workers-shared/asset-worker/tests/kv.test.ts b/packages/workers-shared/asset-worker/tests/kv.test.ts
@@ -65,11 +65,38 @@ describe("[Asset Worker] Fetching assets from KV", () => {
 			spy.mockReturnValue(Promise.reject("Oeps! Something went wrong"));
 
 			await expect(() =>
-				getAssetWithMetadataFromKV(mockKVNamespace, "abcd", 2)
+				getAssetWithMetadataFromKV(mockKVNamespace, "abcd", undefined, 2)
 			).rejects.toThrowError(
 				"Requested asset abcd could not be fetched from KV namespace."
 			);
 			expect(spy).toHaveBeenCalledTimes(3);
 		});
+
+		it("should retry on 404 and cache with 30s ttl", async () => {
+			let attempts = 0;
+			spy.mockImplementation(() => {
+				if (attempts++ === 0) {
+					return Promise.resolve({
+						value: null,
+					}) as unknown as Promise<
+						KVNamespaceGetWithMetadataResult<ReadableStream, AssetMetadata>
+					>;
+				} else {
+					return Promise.resolve({
+						value: "<html>Hello world</html>",
+						metadata: {
+							contentType: "text/html",
+						},
+					}) as unknown as Promise<
+						KVNamespaceGetWithMetadataResult<ReadableStream, AssetMetadata>
+					>;
+				}
+			});
+
+			const asset = await getAssetWithMetadataFromKV(mockKVNamespace, "abcd");
+			expect(asset?.value).toBeTruthy();
+			// Once for the initial call, once for the 404
+			expect(spy).toHaveBeenCalledTimes(2);
+		});
 	});
 });