Troubleshooting Cloudflare “Error 1101: Worker Threw Exception”

Cloudflare Error 1101, also known as “Worker Threw Exception,” is an error that occurs when using Cloudflare Workers. It indicates that there is an issue with the worker code, and an exception has been thrown during the execution of the worker script. This error can happen for various reasons, such as syntax errors, runtime issues, or incorrect logic in the worker code. To resolve Cloudflare Error 1101, the worker code needs to be carefully reviewed and debugged to identify and fix the underlying problem.

Here are the steps our Support Engineers take to figure out what’s wrong:

Step 1: Identifying the Error using Workers Metrics

Checking the Workers Metrics in your Cloudflare dashboard is a good place to start investigating. By going to this area, you can learn useful information about any downtime or errors your application might have. Pay close attention to any patterns or spikes in the metrics that don’t make sense. This could mean that there is something wrong with your Workers program.

Step 2: Debugging Exceptions with Wrangler Tail

Once you’ve found the Workers program that’s giving you errors, it’s time to figure out what’s wrong and fix it. We recommend that you use the “wrangler tail” tool to look at the exceptions as they happen. This tool lets you keep an eye on the logs and find the error-causing exception.

To see the exceptions, look for the “exceptions” field in the JSON returned by “wrangler tail.” Take note of the information given because it will help you figure out what the problem is and how to solve it.

Step 3: Fixing the Exception and Redeploying Code

It’s important to fix the problem and redeploy your code after you’ve found the exception that caused the mistakes. Look at the details of the exception and make the changes to your codebase that you need to fix the problem. After making the necessary changes, you should redeploy your code to the Cloudflare server.

During the process of relocation, we suggest keeping a close eye on the logs by following them. This makes sure that the problem has been fixed and that your app is working as it should.

Step 4: Setting up a Logging Service for Error Collection

Consider setting up a logging service to improve your ability to find and fix problems. You can get error logs from your Worker application by using a tool like Sentry. To do this, an HTTP request must be sent to the logging service to report any problems.

When using this method to log, it’s important to remember that any unfinished asynchronous tasks are cancelled as soon as a Worker finishes sending the client the main answer body. You can use the event to make sure that a record subrequest finishes. You can use the request promise with the waitUntil() function.

addEventListener("fetch", event => {
  event.respondWith(handleEvent(event));
});

async function handleEvent(event) {
  // ...
  event.waitUntil(postLog(stack));
  
  return fetch(event.request);
}

function postLog(data) {
  return fetch("https://log-service.example.com/", {
    method: "POST",
    body: data,
  });
}

By using a logging service, you can learn more about mistakes that happen in your Workers application, which makes it easier to track and analyse them.

Step 5: Go to Origin on Error

You can use the event.passThroughOnException() function to make sure that your website works smoothly even when there are errors. If you turn on this feature in your Workers program, any requests that throw an exception will be sent to your origin server.

With this tool, you can add logging, tracking, or other features to Workers without changing how your site works in general. Here is a small piece of code that shows how to use event.passThroughOnException():

addEventListener("fetch", event => {
  event.passThroughOnException();
  event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
  // An error here will return the origin response, as if the Worker wasn’t present.
  // ...
  return fetch(request);
}

By using the passThroughOnException() method, you can make sure that your website works smoothly even when exceptions happen, while still taking advantage of the benefits of Workers.

Conclusion

Codeyo Genie is here to help, so don’t forget that. If you need more help or would rather have an expert show you the way. Contact us today to improve how your website works and make sure your users can always get to it.