8 FastAPI Logging Best Practices

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints. It is one of the fastest Python frameworks available, as measured by independent benchmarks.

Logging is an important part of any application, and FastAPI is no exception. Logging helps you to identify errors and other issues quickly and easily. In this article, we will discuss 8 best practices for logging with FastAPI. We will cover topics such as logging levels, log rotation, and log aggregation.

1. Use the standard library logging module

The logging module is a built-in Python library that provides a flexible and powerful way to log messages from your application. It allows you to easily configure the level of detail in your logs, as well as customize the format of the output. This makes it easy to quickly identify errors or other important events in your application.

Using the standard library logging module also helps ensure consistency across different applications. Since it’s part of the Python language, all developers are familiar with its syntax and usage. This means that when debugging an issue, everyone on the team can quickly understand what’s going on without having to learn a new system.

FastAPI has built-in support for the logging module, making it easy to integrate into your application. All you need to do is create a logger object and then use the appropriate methods to log messages. You can also set up custom handlers to route log messages to different destinations such as files, databases, or even external services like Slack.

2. Don’t use print() to log messages

The main reason to avoid using print() is that it does not provide the same level of control and flexibility as other logging methods. For example, when using print(), you cannot specify a log level or add additional context information such as timestamps or user IDs. This makes it difficult to debug issues in production environments since there is no way to filter out irrelevant messages.

Additionally, print() statements are often scattered throughout the codebase, making them hard to find and maintain. It also makes it difficult to track down errors since they may be printed anywhere in the code.

A better approach is to use FastAPI’s built-in logger. This provides more control over how messages are logged, including setting log levels, adding contextual information, and formatting logs for easier readability. Additionally, all log messages can be centralized in one place, making them easier to find and maintain.

Using FastAPI’s logger also allows for integration with third-party logging services such as Sentry or Loggly. This makes it easy to monitor application performance and quickly identify any potential issues.

3. Log as much information as possible

Logging as much information as possible is important because it allows developers to quickly identify and debug issues. By logging detailed information, such as the request URL, query parameters, headers, body, response status code, and more, developers can easily pinpoint where an issue occurred and what caused it. This makes debugging faster and easier, which in turn saves time and money.

To log as much information as possible with FastAPI, developers should use a structured logger like Loguru or Python’s built-in logging module. Structured loggers allow developers to log data in a consistent format that can be easily parsed by other tools. For example, Loguru provides support for JSON logging, which allows developers to store their logs in a standard format that can be read by any tool that supports JSON.

When using a structured logger, developers should also make sure to include contextual information in their logs. Contextual information includes things like user IDs, session IDs, IP addresses, and other data points that can help provide additional context about the request being logged. This helps developers better understand how users are interacting with their application and can be invaluable when troubleshooting issues.

4. Log exceptions

Logging exceptions is important because it allows developers to quickly identify and debug errors in their applications. Without exception logging, developers would have to manually search through the codebase for potential issues or rely on users to report them. By logging exceptions, developers can easily pinpoint where an issue occurred and what caused it. This makes debugging much faster and more efficient.

To log exceptions with FastAPI, you need to use a library like Python’s built-in logging module. The logging module provides various levels of logging that allow developers to customize how they want to log exceptions. For example, if you only want to log critical errors, you can set the logging level to “critical”. On the other hand, if you want to log all exceptions, you can set the logging level to “debug”.

Once you’ve configured the logging level, you can then add a logger to your application. You can do this by creating a Logger object and passing it the name of your application as well as the logging level. Then, you can call the logger’s error() method whenever an exception occurs. This will log the exception along with its stack trace so that developers can quickly identify and debug the issue.

5. Add context to your logs

Adding context to your logs helps you quickly identify the source of an issue. Without context, it can be difficult to determine which part of your application is causing a problem. By adding contextual information such as request and response data, user IDs, or other relevant details, you can easily pinpoint where the issue originated from.

Contextual logging also makes debugging easier. When you have more detailed information about what happened in each step of the process, it’s much simpler to trace back the root cause of any errors. This saves time and effort when troubleshooting issues.

You can add context to your FastAPI logs by using structured logging libraries like Loguru or Python’s built-in logging module. Structured logging allows you to store log messages with additional metadata that can be used for filtering and searching. For example, if you want to find all requests made by a particular user, you can use the user ID field to filter out only those entries.

When using FastAPI, you should also consider setting up custom logging levels. This will allow you to control how verbose your logs are and make them easier to read. You can set different levels for different types of events, such as debug, info, warning, error, and critical. This way, you can focus on the most important messages while ignoring less important ones.

6. Use a structured logger

Structured logging is a way of formatting log messages so that they are easier to read and parse. Instead of having plain text logs, structured logs contain key-value pairs which can be used for filtering, searching, and analysis. This makes it much easier to find the information you need in your logs.

Using a structured logger with FastAPI also allows you to easily add context to your logs. For example, you can include request data such as headers, query parameters, and body content. You can also include response data such as status codes and response times. This makes it easy to track performance metrics and debug issues quickly.

FastAPI provides built-in support for structured logging via its Logging middleware. This middleware automatically adds contextual information to each log message, including the request URL, method, and duration. It also includes any errors that occur during the request/response cycle. This makes it easy to identify problems and pinpoint their source.

7. Configure your logger for production

Logging is an essential part of any application, and FastAPI is no exception. Logging helps you track errors, monitor performance, and debug issues in production. Without proper logging, it can be difficult to identify problems or understand how your application is behaving.

Configuring your logger for production ensures that the right information is being logged at the right time. This includes setting up log levels so that only important messages are recorded, as well as configuring the format of the logs so they are easy to read and interpret. Additionally, you should configure your logger to write logs to a persistent storage location such as a file system or database. This will ensure that your logs are not lost if the application crashes or restarts.

When configuring your logger for production, it’s also important to consider security. You should make sure that sensitive data is not included in the logs, and that access to the logs is restricted to authorized personnel.

8. Use an external service to store and analyze logs

Storing Logs Externally

Using an external service to store logs is beneficial because it allows for more efficient log management. By storing the logs externally, they can be accessed from any location and are not limited by the size of the local storage. This makes it easier to search through large amounts of data quickly and accurately. Additionally, using an external service ensures that the logs are secure and protected from unauthorized access.

Analyzing Logs with External Services

External services also provide powerful tools for analyzing logs. These services typically offer a range of features such as real-time monitoring, alerting, and reporting capabilities. This enables users to gain insights into their application performance and identify potential issues before they become major problems. Furthermore, these services often come with built-in analytics tools which allow users to visualize their data in various ways, making it easier to spot trends or anomalies.

Integrating FastAPI with External Services

Integrating FastAPI with an external logging service is relatively straightforward. The first step is to configure the logger within the FastAPI application. This involves setting up the appropriate logging levels and handlers, as well as specifying the format of the log messages. Once this is done, the next step is to set up the connection between the FastAPI application and the external service. This usually involves providing credentials and configuring the API endpoints. Finally, the last step is to start sending the logs to the external service. This can be done either manually or automatically depending on the specific requirements.