fix: keep docker mirror on local builder fallback

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: pbardea

dist/index.js

@@ -25,6 +25,7 @@ import {
   pruneBuildkitCache,
   logBuildCacheContents,
   logDatabaseHashes,
+  writeDockerContainerBuildkitdTomlFile,
 } from "./setup_builder";
 import {
   installBuildKit,
@@ -739,9 +740,11 @@ void actionsToolkit.run(
               `Found configured builder: ${builder.name} (driver: ${builder.driver})`,
             );
           } else {
-            // Create a local builder
-            const createLocalBuilderCmd =
-              "docker buildx create --name local --driver docker-container --use";
+            // Create a local builder with the same Docker Hub mirror config as
+            // the Blacksmith builder so sticky disk failures do not bypass it.
+            const localBuilderConfigPath =
+              await writeDockerContainerBuildkitdTomlFile();
+            const createLocalBuilderCmd = `docker buildx create --name local --driver docker-container --config ${localBuilderConfigPath} --use`;
             try {
               await Exec.exec(createLocalBuilderCmd);
               core.info("Created and set a local builder for use");

dist/index.js.map

@@ -1,5 +1,6 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import * as core from "@actions/core";
+import * as fs from "fs";
 import * as setupBuilder from "./setup_builder";
 // import * as reporter from "./reporter";
 
@@ -84,6 +85,26 @@ describe("setup_builder", () => {
 
   // Tailscale tests removed - not needed for setup-docker-builder
 
+  describe("writeDockerContainerBuildkitdTomlFile", () => {
+    it("writes a docker-container BuildKit config with the Docker mirror", async () => {
+      const writeFile = vi.mocked(fs.promises.writeFile);
+
+      await setupBuilder.writeDockerContainerBuildkitdTomlFile(
+        "local-buildkitd.toml",
+      );
+
+      expect(writeFile.mock.calls[0][0]).toBe("local-buildkitd.toml");
+      const config = writeFile.mock.calls[0][1] as string;
+      expect(config).toContain('mirrors = [ "http://192.168.127.1:5000" ]');
+      expect(config).toContain('[registry."docker.io"]');
+      expect(config).toContain('[registry."192.168.127.1:5000"]');
+      expect(config).not.toContain("[grpc]");
+      expect(core.info).toHaveBeenCalledWith(
+        "Wrote Docker container BuildKit config to local-buildkitd.toml",
+      );
+    });
+  });
+
   describe("logBuildCacheContents", () => {
     it("should log build cache contents from buildctl du", async () => {
       const exec = (await import("child_process")).exec as unknown as {

src/main.ts

@@ -133,6 +133,35 @@ async function getRoutableHostDns(): Promise<string[]> {
   return publicDnsFallback;
 }
 
+function getDockerMirrorRegistryConfig(): TOML.JsonMap {
+  return {
+    "docker.io": {
+      mirrors: ["http://192.168.127.1:5000"],
+      http: true,
+      insecure: true,
+    },
+    "192.168.127.1:5000": {
+      http: true,
+      insecure: true,
+    },
+  };
+}
+
+async function writeTomlConfig(
+  filePath: string,
+  jsonConfig: TOML.JsonMap,
+): Promise<void> {
+  const tomlString = TOML.stringify(jsonConfig);
+
+  try {
+    await fs.promises.writeFile(filePath, tomlString);
+    core.debug(`TOML configuration is ${tomlString}`);
+  } catch (err) {
+    core.warning(`error writing TOML configuration: ${(err as Error).message}`);
+    throw err;
+  }
+}
+
 async function writeBuildkitdTomlFile(
   parallelism: number,
   addr: string,
@@ -151,17 +180,7 @@ async function writeBuildkitdTomlFile(
     dns: {
       nameservers: dnsNameservers,
     },
-    registry: {
-      "docker.io": {
-        mirrors: ["http://192.168.127.1:5000"],
-        http: true,
-        insecure: true,
-      },
-      "192.168.127.1:5000": {
-        http: true,
-        insecure: true,
-      },
-    },
+    registry: getDockerMirrorRegistryConfig(),
     worker: {
       oci: {
         enabled: true,
@@ -177,15 +196,27 @@ async function writeBuildkitdTomlFile(
     },
   };
 
-  const tomlString = TOML.stringify(jsonConfig);
+  await writeTomlConfig("buildkitd.toml", jsonConfig);
+}
 
-  try {
-    await fs.promises.writeFile("buildkitd.toml", tomlString);
-    core.debug(`TOML configuration is ${tomlString}`);
-  } catch (err) {
-    core.warning(`error writing TOML configuration: ${(err as Error).message}`);
-    throw err;
-  }
+export async function writeDockerContainerBuildkitdTomlFile(
+  filePath = "docker-container-buildkitd.toml",
+): Promise<string> {
+  // Keep this config safe for buildx's docker-container driver: it should not
+  // set grpc.address, which buildx owns for the containerized BuildKit daemon.
+  await configureSystemdResolvedForBuildkit();
+  const dnsNameservers = await getRoutableHostDns();
+  const jsonConfig: TOML.JsonMap = {
+    dns: {
+      nameservers: dnsNameservers,
+    },
+    registry: getDockerMirrorRegistryConfig(),
+  };
+
+  await writeTomlConfig(filePath, jsonConfig);
+  core.info(`Wrote Docker container BuildKit config to ${filePath}`);
+
+  return filePath;
 }
 
 export async function startBuildkitd(