Frontera API

This section documents the Frontera core API, and is intended for developers of middlewares and backends.

Frontera API / Manager

The main entry point to Frontera API is the FrontierManager object, passed to middlewares and backend through the from_manager class method. This object provides access to all Frontera core components, and is the only way for middlewares and backend to access them and hook their functionality into Frontera.

The FrontierManager is responsible for loading the installed middlewares and backend, as well as for managing the data flow around the whole frontier.

Loading from settings

Although FrontierManager can be initialized using parameters the most common way of doing this is using Frontera Settings.

This can be done through the from_settings class method, using either a string path:

>>> from frontera import FrontierManager
>>> frontier = FrontierManager.from_settings('')

or a BaseSettings object instance:

>>> from frontera import FrontierManager, Settings
>>> settings = Settings()
>>> settings.MAX_PAGES = 0
>>> frontier = FrontierManager.from_settings(settings)

It can also be initialized without parameters, in this case the frontier will use the default settings:

>>> from frontera import FrontierManager, Settings
>>> frontier = FrontierManager.from_settings()

Frontier Manager

Starting/Stopping the frontier

Sometimes, frontier components need to perform initialization and finalization operations. The frontier mechanism to notify the different components of the frontier start and stop is done by the start() and stop() methods respectively.

By default auto_start frontier value is activated, this means that components will be notified once the FrontierManager object is created. If you need to have more fine control of when different components are initialized, deactivate auto_start and manually call frontier API start() and stop() methods.


Frontier stop() method is not automatically called when auto_start is active (because frontier is not aware of the crawling state). If you need to notify components of frontier end you should call the method manually.

Frontier iterations

Once frontier is running, the usual process is the one described in the data flow section.

Crawler asks the frontier for next pages using the get_next_requests() method. Each time the frontier returns a non empty list of pages (data available), is what we call a frontier iteration.

Current frontier iteration can be accessed using the iteration attribute.

Finishing the frontier

Crawl can be finished either by the Crawler or by the Frontera. Frontera will finish when a maximum number of pages is returned. This limit is controlled by the max_requests attribute (MAX_REQUESTS setting).

If max_requests has a value of 0 (default value) the frontier will continue indefinitely.

Once the frontier is finished, no more pages will be returned by the get_next_requests method and finished attribute will be True.

Component objects

class frontera.core.components.Component

Interface definition for a frontier component The Component object is the base class for frontier Middleware and Backend objects.

FrontierManager communicates with the active components using the hook methods listed below.

Implementations are different for Middleware and Backend objects, therefore methods are not fully described here but in their corresponding section.



The component name

Abstract methods


Called when the frontier starts, see starting/stopping the frontier.


Called when the frontier stops, see starting/stopping the frontier.


This method is called every time a page has been crawled.

Parameters:response (object) – The Response object for the crawled page.
request_error(page, error)

This method is called each time an error occurs when crawling a page.

  • request (object) – The crawled with error Request object.
  • error (string) – A string identifier for the error.

Class Methods

classmethod from_manager(manager)

Class method called from FrontierManager passing the manager itself.

Example of usage:

def from_manager(cls, manager):
    return cls(settings=manager.settings)

Test mode

In some cases while testing, frontier components need to act in a different way than they usually do (for instance domain middleware accepts non valid URLs like 'A1' or 'B1' when parsing domain urls in test mode).

Components can know if the frontier is in test mode via the boolean test_mode attribute.

Other ways of using the frontier

Communication with the frontier can also be done through other mechanisms such as an HTTP API or a queue system. These functionalities are not available for the time being, but hopefully will be included in future versions.