Reporting errors

This tutorial shows how to report and track uncaught exceptions in the Getting started with Python tutorial by using the Google Cloud console.

Error Reporting provides a centralized dashboard that shows counts of each unique error, stack traces, and a history of occurrences. You can also set up an alert for when errors occur.

This page is part of a multipage tutorial. To start from the beginning and read the setup instructions, go to Python Bookshelf app.

Configuring settings

This section uses code in the 5-logging directory. Edit the files and run commands in this directory.

Open the config.py file for editing and replace the following values:

Set the value of [PROJECT_ID] to your project ID, which is visible in the Google Cloud console.
Set the value of [DATA_BACKEND] to the same value you used during the Using structured data tutorial.
If you are using Cloud SQL or MongoDB, set the values under the Cloud SQL or Mongo section to the same values you used during the Using structured data step.
Set the value of [CLOUD_STORAGE_BUCKET] to your Cloud Storage bucket name.
Under the OAuth2 configuration section, set the values of [GOOGLE_OAUTH2_CLIENT_ID] and [GOOGLE_OAUTH2_CLIENT_SECRET] to the application client ID and secret that you created previously.

Save and close the config.py file.

If you are using Cloud SQL:

Open the app.yaml file for editing.
Set the value of cloudsql-instance to the same value used for [CLOUDSQL_CONNECTION_NAME] in the config.py file. Use the format project:region:cloudsql-instance. Uncomment this entire line.
Save and close the app.yaml file.

Installing dependencies

To create a virtual environment and install dependencies, use the following commands:

Linux/macOS

virtualenv -p python3 env
source env/bin/activate
pip install -r requirements.txt

Windows

virtualenv -p python3 env
env\scripts\activate
pip install -r requirements.txt

Running the app on your local machine

Start a local web server:
```
python main.py
```
In your browser, enter the following address:
```
http://localhost:8080
```

Press Control+C to exit the worker and then the local web server.

Deploying the app to the App Engine flexible environment

Deploy the sample app:
```
gcloud app deploy
```
In your browser, enter the following URL:

https://PROJECT_ID.REGION_ID.r.appspot.com

Replace the following:
- PROJECT_ID: Your Google Cloud project ID
- REGION_ID: A code that App Engine assigns to your app

If you update your app, you deploy the updated version by entering the same command that you used to deploy the app. The deployment creates a new version of your app and promotes it to the default version. The earlier versions of your app remain, as do their associated virtual machine (VM) instances. All of these app versions and VM instances are billable resources. To reduce costs, delete the non-default versions of your app.

To delete an app version:

In the Google Cloud console, go to the Versions page for App Engine.
Go to Versions
Select the checkbox for the non-default app version that you want to delete.
Note: The only way you can delete the default version of your App Engine app is by deleting your project. However, you can stop the default version in the Google Cloud console. This action shuts down all instances associated with the version. You can restart these instances later if needed.

In the App Engine standard environment, you can stop the default version only if your app has manual or basic scaling.
To delete the app version, click Delete.

For more information about cleaning up billable resources, see the Cleaning up section in the final step of this tutorial.

Simulate an error

To see Error Reporting in action, intentionally introduce a mistake in your code, and then look for the exception in the Google Cloud console's Error Reporting page.

In bookshelf/crud.py, add an operation that accesses an undefined variable and generates a ReferenceError in the index view.
```
@crud.route("/")
def list():
   x[3]
```
Deploy the app.
```
gcloud app deploy
```
Access the index page.
```
gcloud app browse
```
You can view the message An internal error occurred.
In the Google Cloud console, go to the Error Reporting page:
Go to Error Reporting

You can also find this page by using the search bar.

You can see the error listed.
Click the error to see information about the error, such as when the error was last seen,the number of times the error occurred, a histogram of occurrence times, and the stack trace.

Understanding the code

To report uncaught exceptions, the code first uses the Flask errorhandler decorator, and then reports the exception to Error Reporting by using the Cloud Client Libraries for Python.

@app.errorhandler(500)
def server_error(e):
    client = error_reporting.Client(app.config['PROJECT_ID'])
    client.report_exception(
        http_context=error_reporting.build_flask_context(request))
    return """
    An internal error occurred.
    """, 500

The client automatically adds the traceback info and uses a helper function to extract the relevant request details from the Flask request, which populates Error Reporting with the relevant stack traces and HTTP contexts for any uncaught InternalServerError HTTP 500 exception in your app.

Clean up

To avoid incurring charges to your Google Cloud account for the resources used in this tutorial, either delete the project that contains the resources, or keep the project and delete the individual resources.

The easiest way to eliminate billing is to delete the project that you created for the tutorial.

To delete the project:

In the Google Cloud console, go to the Manage resources page.
Go to Manage resources
In the project list, select the project that you want to delete, and then click Delete.
In the dialog, type the project ID, and then click Shut down to delete the project.

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