Why Does My Go App Build Successfully on Heroku But Fail with an 'Application Error'?

Deploying a Golang App on Heroku: Build Succeeds but Application Error

Initial attempts to deploy a GoLang application to Heroku using Godep support resulted in a successful build but an "Application Error" when accessing the application's endpoint. To troubleshoot this issue, let's delve into the problem and its solution.

Problem Overview:

The deployed app fails to respond when accessing its endpoint (e.g., '/'). The Heroku logs show an error stating that the "Web process failed to bind to $PORT."

Solution:

Heroku requires applications to bind their webservers to the port specified by the PORT environment variable. However, the application code currently starts the server on port 9000.

To resolve this, the application's server should be started on the PORT specified by Heroku. Here's how to do that:

import "os"

func main() {
  // ... (your existing code)

  // Get the port from the PORT environment variable, or default to 9000 if not set
  port := os.Getenv("PORT")
  if port == "" {
      port = "9000" // Default port if not specified
  }

  // Start the server on the specified port
  err := grace.Serve(":" + port, context.ClearHandler(http.DefaultServeMux))

  // ... (your existing code)
}

By binding to the correct port, the application will no longer encounter the "Boot timeout" error and will be able to serve requests successfully on both HTTP and HTTPS ports through Heroku's gateways.

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