I am developing an application using Django that works similar to a project manager. For this reason, the system should be capable of storing information about everything. When I say everything I refer to the actions the users do, the errors that occurred while doing an action, etc.
I have a class Log and one of its attributes is called action_type, this attribute specifies what kind of action just happened. I am supposed to have 5 kinds of types:
INFO: this log stores the information related to user’s actions such as creating a project, create other users, etc.
DEBUG: should store comments made by the developers that will allow them to detect errors.
ERROR: shows errors that occurred in the system but they don’t affect the system’s functionality.
WARNING: it’s for potentially damaging actions.
FATAL: unexpected errors, exceptions and security breaches.
I can only come up with logical logs for INFO.
Could you tell me some reasonable logs that I should include in this and the other categories?
The answer will depend greatly on exactly what your application does, but my basic approach is this:
Each time you get ready to log an event, just think about the event and it will be clear where it belongs. Did it kill your application? It’s fatal. Did it prevent something from working correctly? It’s an error. Could it prevent something from working, and did we just get lucky this time? It’s a warning. Does anyone care? Info. Otherwise, if you still need to log it, it must be for debugging purposes.
In your particular context, it sounds like you might only be trying to log user actions. If that is the case, the only actions that could be fatal would be ones for which you don’t provide an undo option (or, I suppose, if the user is able to order a piano bench and a length of strong rope through your application). I also couldn’t really imagine any debug-level logs coming from user actions. Because of this, I assume you will be logging code level events in addition to user actions.
FATAL: This should only appear in the logs when your application actually crashes, and possibly alongside 500 responses. You might generate these within your wsgi application in a catch-all, only when the process would otherwise have died.
ERROR: Likely tied to http error responses. This is typically for errors caused by something outside your application. Things that happen in your code are probably expected and <= warning level, or unexpected and fatal. Errors might be a 404 from the user making a typo in a url, validation errors on form submission, or authentication errors. From the other direction, errors might be returned from remote web services that you contact or IO errors from the os.
WARNING: For things that don’t break anything, but that might bite you if you keep it up. Examples are using deprecated apis and anywhere something only worked because of the default (time zone, character encoding, etc). Maybe certain input values result in warnings, too, like setting a due date in the past.
INFO: General, healthy operation. Someone created a database row (a new project or a task?), created an account, logged in or out, a socket was successfully opened, etc.
DEBUG: Just what it says. Output that you will usually turn off once the code is working correctly. Method entry/exit, object instantiation, field values at various points in the code, counters. Whatever you need to figure out why your program is crashing right now, as you work on it.