Startup Hangs on Early Errors in GoAlert and Prevents Troubleshooting

[mastercactapus]

Describe the Bug: GoAlert hangs if there's an error early during the startup process. This problematic condition makes it difficult to troubleshoot, as the process hangs indefinitely and doesn't print the actual error for admin to investigate. Moreover, even though it is hanged, the bound address allows health checks to connect. However, those health checks will hang too as the HTTP handler isn't fully registered due to incomplete startup.

Steps to Reproduce:

1. Go to 'app/runapp.go'.

2. Add an early return with an error message as follows:

       eventCtx, cancel := context.WithCancel(ctx)
       defer cancel()
       eventDoneCh, err := app.listenEvents(eventCtx)
       return fmt.Errorf("test")
       if err != nil {
           return err
       }

3. Start the GoAlert system.

4. Observe that the logs show config loaded and hang indefinitely without printing the Listening message.

Expected Behavior: If there's an error during the startup process, the system shouldn't hang and should report the error accurately to enable efficient troubleshooting. Furthermore, health checks should either fail or complete rather than hanging indefinitely.

Observed Behavior: When there's an error during the startup process, the system hangs, doesn't print any error, and makes health checks hang indefinitely, making it difficult for an admin to troubleshoot the issue.

Application Version: This issue is observed in the current master version of GoAlert.

Additional Context: The start-up issue specifically happens when there's an early return error during the startup process.

[Root-acess]

This bug occurs due to an error handling issue during GoAlert's startup, where any early error causes the application to hang instead of cleanly exiting and providing a clear error message. This behavior not only fails to log the error but also leaves the health checks in a hung state, which complicates troubleshooting for administrators.

Analysis of the Issue

1. Cause of Hanging:

   • The startup process begins by initializing key services and setting up event listeners. If an error occurs early (for example, during event listener setup), the process doesn’t exit as expected.
   • Specifically, after encountering an error, the function attempts to return it, but incomplete cleanup and missed cancellation handling leave the process in a hung state.

2. Health Check Issue:

   • Because the application binds to a network address before full initialization, health checks can connect. However, the HTTP handlers necessary to respond are not yet fully registered, causing those health checks to hang indefinitely as well.

3. Logging Gap:

   • The startup log, which should ideally report the listening state or any errors, doesn’t print anything useful, leaving the system administrator without essential information.

Steps to Reproduce

1. Simulate Early Error:
   • In app/runapp.go, simulate an early error by adding an immediate return after event listener initialization.

     eventCtx, cancel := context.WithCancel(ctx)
     defer cancel()
     eventDoneCh, err := app.listenEvents(eventCtx)
     return fmt.Errorf("test") // Simulate an early error
     if err != nil {
     return err
     }

2. Run the Application:
   • Start GoAlert with the modified code.
3. Observe Behavior:
   • Notice that the logs will indicate the configuration loading and then hang indefinitely, without reaching the "Listening" message.

Expected vs. Observed Behavior

• Expected: Upon encountering an error during startup, GoAlert should:
  • Log the error message to assist in troubleshooting.
  • Exit the process cleanly without binding to the address.
  • Return a non-zero exit code to indicate failure.
• Observed: The system hangs indefinitely, without logging the error or cleanly stopping. Health checks can connect but remain hung as HTTP handlers are not fully registered.

Solution

To resolve this, we need to improve error handling during the startup phase by ensuring that:

1. Early Exits Log Errors: Any early errors should be logged before the function returns.
2. Health Checks Don’t Bind on Failure: Bind to the network only after confirming successful initialization.
3. Graceful Exit on Error: Ensure that errors trigger a clean exit, canceling all associated contexts and stopping the process.

Implementation Steps

1. Refactor Initialization Order:
   • Move the network binding step to occur after all essential components (like event listeners) are successfully initialized.
2. Log Errors Before Return:
   • Add error handling to ensure any encountered error is logged before returning.
3. Ensure Cleanup and Cancellation:
   • Use defer statements to handle context cancellation and any other necessary cleanup. This helps to avoid any leftover goroutines or services in an active state, which can cause hanging.

Example Code Adjustment

eventCtx, cancel := context.WithCancel(ctx)
defer cancel()

// Attempt to set up event listeners
eventDoneCh, err := app.listenEvents(eventCtx)
if err != nil {
    log.Errorf("Startup error: %v", err)
    return err // Clean exit with logged error
}

// Continue startup only after successful listener setup
// Bind network address here, after confirming no errors

Expected Outcome After Fix

1. Error Reporting: Any early errors during startup will be logged, making it easy to identify the problem.
2. Clean Exit: The application will not bind to the network if an error occurs during initialization, resulting in a clear failure state rather than a hang.
3. Failing Health Checks: Health checks will not bind to the address unless GoAlert successfully completes startup, providing accurate health status to external systems.

Additional

1. Testing: Add unit and integration tests to simulate early startup failures and verify clean shutdown behavior.
2. Health Check Monitoring: Consider adding checks that ensure HTTP handlers are fully registered before accepting health checks, to avoid partial or incomplete startup states.