How to Fix Go Build Failed on Vercel

Troubleshooting Guide: “Go Build Failed” on Vercel

As a Senior DevOps Engineer, encountering a “Go Build Failed” error on Vercel can be a common roadblock, especially when transitioning from a local development environment. This guide will walk you through the typical causes and provide actionable solutions to get your Go application deployed successfully.

1. The Root Cause: Why This Happens on Vercel

Vercel provides a highly optimized, ephemeral build environment. While convenient, this clean slate approach often means that what works locally might encounter issues in a cloud build pipeline. Here are the primary reasons a “Go Build Failed” error occurs on Vercel:

  • Go Version Mismatch: Your project might require a specific Go version that differs from Vercel’s default, or one that isn’t explicitly configured.
  • Missing or Corrupted go.mod/go.sum: These files are critical for Go module dependency resolution. If they are not committed, out of sync, or contain local path replace directives, the build will fail.
  • Unresolved Dependencies: Vercel’s build environment needs to fetch all your project’s dependencies. Issues can arise if:
    • Dependencies are private and Vercel lacks authentication.
    • A dependency is unavailable via the default GOPROXY (e.g., proxy.golang.org).
    • Network issues prevent Vercel from reaching the module source.
  • Incorrect Main Package Path: Vercel needs to know which Go file or directory contains your main package to build the executable. An incorrect src path in vercel.json can lead to build failures.
  • Local-Only Configurations: If your go.mod uses replace directives pointing to local file paths (e.g., replace example.com/my/module => ../my/module), these will break in Vercel’s isolated environment.
  • Build Output Issues: While less common for basic Go API deployments, if your build process expects a specific output directory that Vercel isn’t configured for, it can cause problems.

2. Quick Fix (CLI)

Before diving into configuration files, try these CLI-based steps to diagnose or resolve the issue:

  1. Ensure Local Build Success: First, verify that your project builds without errors locally. Navigate to your project’s root directory and run:

    go mod tidy
go build ./...

    Resolve any local errors before attempting a Vercel deployment. go mod tidy ensures your go.mod and go.sum files are consistent and up-to-date.

  2. Force a Fresh Vercel Build: Sometimes, Vercel’s cache might contain stale data. Forcing a fresh build can often resolve transient issues.

    vercel deploy --prod --force

    The --force flag ensures Vercel bypasses its build cache and performs a completely new build from your source code.

  3. Inspect Local go.mod for replace Directives: Open your go.mod file and check for any replace directives. If they point to local file paths (e.g., replace example.com/module => ../local/module), these must be removed or updated to point to public/accessible module paths before deploying to Vercel.

3. Configuration Check

The core of resolving “Go Build Failed” often lies in correctly configuring your Vercel project and Go modules.

3.1. vercel.json Configuration

The vercel.json file in your project’s root is crucial for telling Vercel how to build your Go application.

  • Specify Go Builder and Version: Ensure you’re using the correct @vercel/go builder and specify the exact Go version your project requires. This is the most common fix for Go version mismatches.

    // vercel.json
{
  "builds": [
    {
      "src": "api/*.go", // Or your main package path, e.g., "main.go"
      "use": "@vercel/go@3.x", // Use the latest major version compatible with your Go project
      "config": {
        "maxLambdaSize": "50mb", // Optional: Increase if your Go binary is large
        "runtime": "go1.22" // Explicitly specify Go runtime version (e.g., go1.22, go1.21)
      }
    }
  ],
  "routes": [
    {
      "src": "/api/(.*)",
      "dest": "/api/$1"
    }
  ]
}
    • src: Point this to the entry point of your Go application. For a typical API function, this might be api/*.go if your handlers are in an api directory. If your main executable is main.go in the root, use main.go.
    • use: Always use the latest stable version of @vercel/go builder compatible with your Go version. 3.x supports Go 1.16+.
    • config.runtime: Explicitly set the Go version (e.g., go1.22, go1.21) that matches your go.mod file and local development environment.

  • Environment Variables (env): If your project uses private Go modules or requires specific GOPROXY settings, define them in vercel.json or through Vercel’s dashboard Project Settings > Environment Variables.

    // vercel.json (example for private modules)
{
  "builds": [
    {
      "src": "api/*.go",
      "use": "@vercel/go@3.x",
      "config": {
        "runtime": "go1.22"
      }
    }
  ],
  "env": {
    "GOPRIVATE": "github.com/my-org/*", // Your private module paths
    "GIT_CREDENTIALS": "@git_credentials_token" // Example for private Git access token
  }
}
    • GOPRIVATE: A comma-separated list of glob patterns for module paths that should not use the Go module proxy.
    • Private Repository Tokens: If you’re pulling from private Git repositories, you’ll need to provide credentials. The safest way is to add a sensitive token (e.g., GitHub Personal Access Token with repo scope) as an Environment Variable in your Vercel project settings (not directly in vercel.json) and refer to it as GIT_CREDENTIALS or similar. The Go builder will then use this. Ensure your token has read access to the necessary repositories.

3.2. go.mod and go.sum Integrity

  • Commit go.mod and go.sum: These files must be present and committed to your Git repository. Vercel’s build process relies on them to resolve dependencies.
  • Remove Local replace Directives: As mentioned, any replace directives in go.mod that point to local file paths will cause build failures on Vercel. Remove them or update them to public/accessible module paths.
  • Go Version in go.mod: Ensure the go 1.x directive in your go.mod file matches the runtime version specified in vercel.json (e.g., go 1.22 in go.mod should correspond to "runtime": "go1.22").

4. Verification

After applying any of the fixes above, the next critical step is to verify the deployment.

  1. Trigger a New Deployment: Push your changes to your Git repository, or manually trigger a new deployment from the Vercel dashboard.

  2. Inspect Vercel Build Logs:

    • Navigate to your project on the Vercel Dashboard.
    • Click on the failed deployment.
    • Go to the “Build Logs” tab.
    • Crucially, read the logs from top to bottom. The actual error message (e.g., “module not found”, “cannot find package”, “unrecognized import path”) is often buried amongst other build output. Look for error, failed, or specific Go-related messages. This will pinpoint the exact cause if the issue persists.

  3. Test the Deployed Application: Once the deployment shows “Ready” (green status), visit the deployment URL. Test your Go endpoints to ensure the application functions as expected and all dependencies are correctly integrated.

By systematically following these steps, you should be able to diagnose and resolve most “Go Build Failed” errors on Vercel, ensuring a smooth deployment for your Go applications.

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