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fix: check for existing buildkitd before mounting sticky disk #65

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fix: check for existing buildkitd before mounting sticky disk #65

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48 changes: 27 additions & 21 deletions src/main.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -428,6 +428,27 @@ async function startBlacksmithBuilder(
inputs: Inputs,
): Promise<{ addr: string | null; exposeId: string }> {
try {
// If buildkitd is already running, skip - the builder is already initialized.
try {
const { stdout } = await execAsync("pgrep buildkitd");
if (stdout.trim()) {
core.info(
`Detected existing buildkitd process (PID: ${stdout.trim()}). ` +
`Skipping builder setup - builder is already initialized.`,
);
return { addr: null, exposeId: "" };
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@cursor cursor bot Mar 10, 2026

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nofallback check bypassed when buildkitd already running

Low Severity

When buildkitd is already running, the early return { addr: null, exposeId: "" } bypasses the nofallback check in the catch block. The fallback path at line 643+ has no nofallback guard of its own, so if toolkit.builder.inspect() returns null, a local docker-container builder is silently created even when nofallback is true. Previously, detecting a running buildkitd threw an error that respected the nofallback flag.

Additional Locations (1)
Fix in Cursor Fix in Web

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@chadxz chadxz Mar 10, 2026 •
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In this scenario, buildkitd is already running from a prior invocation in the same job - the Blacksmith builder setup already succeeded. There's nothing to "fall back" from, so I don't think nofallback applies here. We're reusing the existing (already working) builder, not necessarily falling back to a local one.

If we later enrich the toolkit.builder.inspect() check to validate that the existing builder is specifically a Blacksmith builder, it may make sense to wire in specific nofallback handling at that point.

}
} catch (error) {
if ((error as { code?: number }).code !== 1) {
// pgrep returns exit code 1 when no process found, which is what we want
// Any other error code indicates a real problem
throw new Error(
`Failed to check for existing buildkitd process: ${(error as Error).message}`,
);
}
// Exit code 1 means no buildkitd process found, which is good - we can proceed
}

// Setup sticky disk
const stickyDiskStartTime = Date.now();
const stickyDiskSetup = await setupStickyDisk();
Expand Down Expand Up @@ -464,25 +485,6 @@ async function startBlacksmithBuilder(
parallelism = inputs["max-parallelism"];
}

// Check if buildkitd is already running before starting
try {
const { stdout } = await execAsync("pgrep buildkitd");
if (stdout.trim()) {
throw new Error(
`Detected existing buildkitd process (PID: ${stdout.trim()}). Refusing to start to avoid conflicts.`,
);
}
} catch (error) {
if ((error as { code?: number }).code !== 1) {
// pgrep returns exit code 1 when no process found, which is what we want
// Any other error code indicates a real problem
throw new Error(
`Failed to check for existing buildkitd process: ${(error as Error).message}`,
);
}
// Exit code 1 means no buildkitd process found, which is good - we can proceed
}

// Check for potential boltdb corruption
const boltdbIntegrity = await checkBoltDbIntegrity(
inputs["skip-integrity-check"],
Expand Down Expand Up @@ -639,8 +641,12 @@ void actionsToolkit.run(
core.info("Blacksmith builder is ready for use by Docker");
});
} else {
// Fallback to local builder
core.warning("Failed to setup Blacksmith builder, using local builder");
// Fallback: either Blacksmith builder setup failed, or buildkitd was
// already running. In both cases, reuse whatever builder is already
// configured.
core.warning(
"Blacksmith builder setup skipped or failed, checking for existing configured builder",
);
await core.group(`Checking for configured builder`, async () => {
try {
const builder = await toolkit.builder.inspect();
Expand Down
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