Support hostname-specific fallbacks

README.md

@@ -150,6 +150,22 @@ REGISTRIES_JSON = "[{ \"registry\": \"https://index.docker.io/\" }]"
 
 You can also set your `docker.io` credentials in the configuration to not have any rate-limiting.
 
+#### Routing fallbacks by hostname
+
+You can route requests from different hostnames to different fallback registries. Add a `hostnames` array to each registry configuration:
+
+```jsonc
+// wrangler.jsonc
+"REGISTRIES_JSON": "[{ \"registry\": \"https://index.docker.io/\", \"hostnames\": [\"docker-mirror.example.com\"] }, { \"registry\": \"https://quay.io/\", \"hostnames\": [\"quay-mirror.example.com\"] }]"
+```
+
+```toml
+# wrangler.toml
+REGISTRIES_JSON = "[{ \"registry\": \"https://index.docker.io/\", \"hostnames\": [\"docker-mirror.example.com\"] }, { \"registry\": \"https://quay.io/\", \"hostnames\": [\"quay-mirror.example.com\"] }]"
+```
+
+Configurations without `hostnames` remain default fallbacks. If a request matches one or more hostname-specific configurations, the registry only tries those matches. Otherwise, it tries the default fallbacks.
+
 ### Known limitations
 
 Right now there is some limitations with this container registry.

src/registry/registry.ts

@@ -8,6 +8,7 @@ import { GarbageCollectionMode } from "./garbage-collector";
 const registryConfiguration = z
   .object({
     registry: z.url(),
+    hostnames: z.array(z.string().min(1)).min(1).optional(),
   })
   .and(
     z
@@ -24,14 +25,27 @@ const registryConfiguration = z
   );
 export type RegistryConfiguration = z.infer<typeof registryConfiguration>;
 
-export function registries(env: Env): RegistryConfiguration[] {
+export function registries(env: Env, hostname?: string): RegistryConfiguration[] {
   if (env.REGISTRIES_JSON === undefined || env.REGISTRIES_JSON.length === 0) {
     return [];
   }
 
   try {
     const jsonObject = JSON.parse(env.REGISTRIES_JSON);
-    return registryConfiguration.array().parse(jsonObject);
+    const configurations = registryConfiguration.array().parse(jsonObject);
+    if (hostname === undefined) {
+      return configurations;
+    }
+
+    const normalizedHostname = hostname.toLowerCase();
+    const matchingConfigurations = configurations.filter((configuration) =>
+      configuration.hostnames?.some((configuredHostname) => configuredHostname.toLowerCase() === normalizedHostname),
+    );
+    if (matchingConfigurations.length > 0) {
+      return matchingConfigurations;
+    }
+
+    return configurations.filter((configuration) => configuration.hostnames === undefined);
   } catch (err) {
     console.error("Error parsing registries JSON: " + errorString(err));
     return [];

src/router.ts

@@ -153,7 +153,7 @@ v2Router.head("/:name+/manifests/:reference", async (req, env: Env) => {
   }
 
   let checkManifestResponse: CheckManifestResponse | null = null;
-  const registryList = registries(env);
+  const registryList = registries(env, new URL(req.url).hostname);
   for (const registry of registryList) {
     const client = new RegistryHTTPClient(env, registry);
     const response = await client.manifestExists(name, reference);
@@ -225,7 +225,7 @@ v2Router.get("/:name+/manifests/:reference", async (req, env: Env, context: Exec
   }
 
   let getManifestResponse: GetManifestResponse | null = null;
-  const registriesList = registries(env);
+  const registriesList = registries(env, new URL(req.url).hostname);
   for (const registry of registriesList) {
     const client = new RegistryHTTPClient(env, registry);
     const response = await client.getManifest(name, reference);
@@ -371,7 +371,7 @@ v2Router.get("/:name+/blobs/:digest", async (req, env: Env, context: ExecutionCo
   }
 
   let layerResponse: GetLayerResponse | null = null;
-  const registriesList = registries(env);
+  const registriesList = registries(env, new URL(req.url).hostname);
   for (const registry of registriesList) {
     const client = new RegistryHTTPClient(env, registry);
     const response = await client.getLayer(name, digest);
@@ -593,7 +593,7 @@ v2Router.head("/:name+/blobs/:tag", async (req, env: Env) => {
   const res = await env.REGISTRY.head(`${name}/blobs/${tag}`);
   let layerExistsResponse: CheckLayerResponse | null = null;
   if (!res) {
-    const registryList = registries(env);
+    const registryList = registries(env, new URL(req.url).hostname);
     for (const registry of registryList) {
       const client = new RegistryHTTPClient(env, registry);
       const response = await client.layerExists(name, tag);

test/index.test.ts

@@ -1398,6 +1398,52 @@ test("registries configuration", async () => {
   }
 });
 
+test("registries configuration supports hostname-specific fallbacks", () => {
+  const bindings = {
+    ...(env as Env),
+    REGISTRIES_JSON: JSON.stringify([
+      {
+        registry: "https://index.docker.io/",
+        hostnames: ["docker-mirror.example.com"],
+      },
+      {
+        registry: "https://quay.io/",
+        hostnames: ["quay-mirror.example.com"],
+      },
+      {
+        registry: "https://docker-secondary.example.com/",
+        hostnames: ["docker-mirror.example.com"],
+      },
+      {
+        registry: "https://default.example.com/",
+      },
+    ]),
+  };
+
+  expect(registries(bindings, "docker-mirror.example.com")).toEqual([
+    {
+      registry: "https://index.docker.io/",
+      hostnames: ["docker-mirror.example.com"],
+    },
+    {
+      registry: "https://docker-secondary.example.com/",
+      hostnames: ["docker-mirror.example.com"],
+    },
+  ]);
+  expect(registries(bindings, "QUAY-MIRROR.EXAMPLE.COM")).toEqual([
+    {
+      registry: "https://quay.io/",
+      hostnames: ["quay-mirror.example.com"],
+    },
+  ]);
+  expect(registries(bindings, "other.example.com")).toEqual([
+    {
+      registry: "https://default.example.com/",
+    },
+  ]);
+  expect(registries(bindings)).toHaveLength(4);
+});
+
 describe("http client", () => {
   const bindings = env as Env;
   let envBindings = { ...bindings };