# 3.3.4. Configuration

Wherever possible, Buildbot components should access configuration information as needed from the canonical source, `master.config`, which is an instance of `MasterConfig`. For example, components should not keep a copy of the `buildbotURL` locally, as this value may change throughout the lifetime of the master.

Components which need to be notified of changes in the configuration should be implemented as services, subclassing `ReconfigurableServiceMixin`, as described in Reconfiguration.

class buildbot.config.MasterConfig

  The master object makes much of the configuration available from an object named `master.config`. Configuration is stored as attributes of this object. Where possible, other Buildbot components should access this configuration directly and not cache the configuration values anywhere else. This avoids the need to ensure that update-from-configuration methods are called on a reconfig.

  Aside from validating the configuration, this class handles any backward-compatibility issues - renamed parameters, type changes, and so on - removing those concerns from other parts of Buildbot.

  This class may be instantiated directly, creating an entirely default configuration, or via `FileLoader.loadConfig`, which will load the configuration from a config file.

  The following attributes are available from this class, representing the current configuration. This includes a number of global parameters:

  title

    The title of this buildmaster, from `title`.

  titleURL

    The URL corresponding to the title, from `titleURL`.

  buildbotURL

    The URL of this buildmaster, for use in constructing WebStatus URLs; from `buildbotURL`.

  logCompressionLimit

    The current log compression limit, from `logCompressionLimit`.

  logCompressionMethod

    The current log compression method, from `logCompressionMethod`.

  logMaxSize

    The current log maximum size, from `logMaxSize`.

  logMaxTailSize

    The current log tail maximum size, from `logMaxTailSize`.

  logEncoding

    The encoding to expect when logs are provided as bytestrings, from `logEncoding`.

  properties

    A `Properties` instance containing global properties, from `properties`.

  collapseRequests

    A callable, or True or False, describing how to collapse requests; from `collapseRequests`.

  prioritizeBuilders

    A callable, or None, used to prioritize builders; from `prioritizeBuilders`.

  codebaseGenerator

    A callable, or None, used to determine the codebase from an incoming `Change`, from `codebaseGenerator`.

  protocols

    The per-protocol port specification for worker connections; based on `protocols`.

  multiMaster

    If true, then this master is part of a cluster; based on `multiMaster`.

  manhole

    The manhole instance to use, or None; from `manhole`.

  The remaining attributes contain compound configuration structures, usually as dictionaries:

  validation

    Validation regular expressions, a dictionary from `validation`. It is safe to assume that all expected keys are present.

  db

    Database specification, a dictionary with key `db_url`. It is safe to assume that this key is present.

  metrics

    The metrics configuration from `metrics`, or an empty dictionary by default.

  caches

    The cache configuration, from `caches` as well as the deprecated `buildCacheSize` and `changeCacheSize` parameters.

    The keys `Builds` and `Caches` are always available; other keys should use `config.caches.get(cachename, 1)`.

  schedulers

    The dictionary of scheduler instances, by name, from `schedulers`.

  builders

    The list of `BuilderConfig` instances from `builders`. Builders specified as dictionaries in the configuration file are converted to instances.

  workers

    The list of `Worker` instances from `workers`.

  change_sources

    The list of `IChangeSource` providers from `change_source`.

  user_managers

    The list of user managers providers from `user_managers`.

  www

    The web server configuration from `www`. The keys `port` and `url` are always available.

  services

    The list of additional plugin services.

  classmethod loadFromDict(config_dict, filename)
    Parameters:

      - config_dict (dict) – The dictionary containing the configuration to load

      - filename (string) – The filename to use when reporting errors

    Returns:

      new `MasterConfig` instance

    Load the configuration from the given dictionary.

Loading of the configuration file is generally triggered by the master, using the following class:

class buildbot.config.FileLoader
  __init__(basedir, filename)
    Parameters:

      - basedir (string) – directory to which config is relative

      - filename (string) – the configuration file to load

    The filename is treated as relative to basedir if it is not absolute.

  loadConfig(basedir, filename)
    Returns:

      new `MasterConfig` instance

    Load the configuration in the given file. Aside from syntax errors, this will also detect a number of semantic errors such as multiple schedulers with the same name.

buildbot.config.loadConfigDict(basedir, filename)
  Parameters:

    - basedir (string) – directory to which config is relative

    - filename (string) – the configuration file to load

  Raises:

    `ConfigErrors` if any errors occur

  Returns dict:

    The `BuildmasterConfig` dictionary.

  Load the configuration dictionary in the given file.

  The filename is treated as relative to basedir if it is not absolute.

## 3.3.4.1. Builder Configuration

class buildbot.config.BuilderConfig([keyword args])

  This class parameterizes configuration of builders; see Builder Configuration for its arguments. The constructor checks for errors, applies defaults, and sets the properties described here. Most are simply copied from the constructor argument of the same name.

  Users may subclass this class to add defaults, for example.

  name

    The builder’s name.

  factory

    The builder’s factory.

  workernames

    The builder’s worker names (a list, regardless of whether the names were specified with `workername` or `workernames`).

  builddir

    The builder’s builddir.

  workerbuilddir

    The builder’s worker-side builddir.

  category

    The builder’s category.

  nextWorker

    The builder’s nextWorker callable.

  nextBuild

    The builder’s nextBuild callable.

  canStartBuild

    The builder’s canStartBuild callable.

  locks

    The builder’s locks.

  env

    The builder’s environment variables.

  properties

    The builder’s properties, as a dictionary.

  collapseRequests

    The builder’s collapseRequests callable.

  description

    The builder’s description, displayed in the web status.

## 3.3.4.2. Error Handling

If any errors are encountered while loading the configuration, `buildbot.config.error` should be called. This can occur both in the configuration-loading code, and in the constructors of any objects that are instantiated in the configuration - change sources, workers, schedulers, build steps, and so on.

buildbot.config.error(error)
  Parameters:

    error – error to report

  Raises:

    `ConfigErrors` if called at build-time

  This function reports a configuration error. If a config file is being loaded, then the function merely records the error, and allows the rest of the configuration to be loaded. At any other time, it raises `ConfigErrors`. This is done so that all config errors can be reported, rather than just the first one.

exception buildbot.config.ConfigErrors([errors])
  Parameters:

    errors (list) – errors to report

  This exception represents errors in the configuration. It supports reporting multiple errors to the user simultaneously, e.g., when several consistency checks fail.

  errors

    A list of detected errors, each given as a string.

  addError(msg)
    Parameters:

      msg (string) – the message to add

    Add another error message to the (presumably not-yet-raised) exception.

# 3.3.5. Configuration in AngularJS

The AngularJS frontend often needs access to the local master configuration. This is accomplished automatically by converting various pieces of the master configuration to a dictionary.

The `IConfigured` interface represents a way to convert any object into a JSON-able dictionary.

class buildbot.interfaces.IConfigured

  Providers of this interface provide a method to get their configuration as a dictionary:

  getConfigDict()
    Returns:

      object

    Return the configuration of this object. Note that despite the name, the return value may not be a dictionary.

  Any object can be “cast” to an `IConfigured` provider. The `getConfigDict` method for basic Python objects simply returns the value.

      IConfigured(someObject).getConfigDict()

class buildbot.util.ConfiguredMixin

  This class is a basic implementation of `IConfigured`. Its `getConfigDict` method simply returns the instance’s `name` attribute (all objects configured must have the `name` attribute).

  getConfigDict()
    Returns:

      object

    Return a config dictionary representing this object.

All of this is used by to serve `/config.js` to the JavaScript frontend.

## 3.3.5.1. Reconfiguration

When the buildmaster receives a signal to begin a reconfig, it re-reads the configuration file, generating a new `MasterConfig` instance, and then notifies all of its child services via the reconfig mechanism described below. The master ensures that at most one reconfiguration is taking place at any time.

See Master Organization for the structure of the Buildbot service tree.

To simplify initialization, a reconfiguration is performed immediately on master startup. As a result, services only need to implement their configuration handling once, and can use `startService` for initialization.

See below for instructions on implementing configuration of common types of components in Buildbot.

Note

Because Buildbot uses a pure-Python configuration file, it is not possible to support all forms of reconfiguration. In particular, when the configuration includes custom subclasses or modules, reconfiguration can turn up some surprising behaviors due to the dynamic nature of Python. The reconfig support in Buildbot is intended for “intermediate” uses of the software, where there are fewer surprises.

### Reconfigurable Services

Instances which need to be notified of a change in configuration should be implemented as Twisted services and mix in the `ReconfigurableServiceMixin` class, overriding the `reconfigServiceWithBuildbotConfig` method.

The services implementing `ReconfigurableServiceMixin` operate on whole master configuration.

In some cases they are effectively singletons that handle configuration identified by a specific configuration key. Such singletons often manage non-singleton services as children and pass bits of its own configuration when reconfiguring these children. `BuildbotServiceManager` is one internal implementation of `ReconfigurableServiceMixin` which accepts a list of child service configurations as its configuration and then intelligently reconfigures child services on changes.

Non-singleton `ReconfigurableServiceMixin` services are harder to write as they must manually pick its configuration from whole master configuration. The parent service also needs explicit support for this kind of setup to work correctly.

class buildbot.config.ReconfigurableServiceMixin
  reconfigServiceWithBuildbotConfig(new_config)
    Parameters:

      new_config (`MasterConfig`) – new master configuration

    Returns:

      Deferred

    This method notifies the service that it should make any changes necessary to adapt to the new configuration values given.

    This method will be called automatically after a service is started.

    It is generally too late at this point to roll back the reconfiguration, so if possible, any errors should be detected in the `MasterConfig` implementation. Errors are handled as best as possible and communicated back to the top level invocation, but such errors may leave the master in an inconsistent state. `ConfigErrors` exceptions will be displayed appropriately to the user on startup.

    Subclasses should always call the parent class’s implementation. For `MultiService` instances, this will call any child services’ `reconfigService` methods, as appropriate. This will be done sequentially, such that the Deferred from one service must fire before the next service is reconfigured.

  priority

    Child services are reconfigured in order of decreasing priority. The default priority is 128, so a service that must be reconfigured before others should be given a higher priority.

### Change Sources

When reconfiguring, there is no method by which Buildbot can determine that a new `ChangeSource` represents the same source as an existing `ChangeSource`, but with different configuration parameters. As a result, the change source manager compares the lists of existing and new change sources using equality, stops any existing sources that are not in the new list, and starts any new change sources that do not already exist.

`ChangeSource` inherits `ComparableMixin`, so change sources are compared based on the attributes described in their `compare_attrs`.

If a change source does not make reference to any global configuration parameters, then there is no need to inherit `ReconfigurableServiceMixin`, as a simple comparison and `startService` and `stopService` will be sufficient.

If the change source does make reference to global values, e.g., as default values for its parameters, then it must inherit `ReconfigurableServiceMixin` to support the case where the global values change.

### Schedulers

Schedulers have names, so Buildbot can determine whether a scheduler has been added, removed, or changed during a reconfig. Old schedulers will be stopped, new schedulers will be started, and both new and existing schedulers will see a call to `reconfigService`, if such a method exists. For backward compatibility, schedulers that do not support reconfiguration will be stopped, and a new scheduler will be started when their configuration changes.

During a reconfiguration, if a new and old scheduler’s fully qualified class names differ, then the old class will be stopped, and the new class will be started. This supports the case when a user changes, for example, a `Nightly` scheduler to a `Periodic` scheduler without changing the name.

Because Buildbot uses `ReconfigurableBaseScheduler` instances directly in the configuration file, a reconfigured scheduler must extract its new configuration information from another instance of itself.

#### Custom Subclasses

Custom subclasses are most often defined directly in the configuration file, or in a Python module that is reloaded with `reload` every time the configuration is loaded. Because of the dynamic nature of Python, this creates a new object representing the subclass every time the configuration is loaded – even if the class definition has not changed.

Note that if a scheduler’s class changes in a reconfig, but the scheduler’s name does not, it will still be treated as a reconfiguration of the existing scheduler. This means that implementation changes in custom scheduler subclasses will not be activated with a reconfig. This behavior avoids stopping and starting such schedulers on every reconfig, but can make development difficult.

One workaround for this is to change the name of the scheduler before each reconfig - this will cause the old scheduler to be stopped, and the new scheduler (with the new name and class) to be started.

### Workers

Similar to schedulers, workers are specified by name, so new and old configurations are first compared by name, and any workers to be added or removed are noted. Workers for which the fully-qualified class name has changed are also added and removed. All workers have their `reconfigService` method called.

This method takes care of the basic worker attributes, including changing the PB registration if necessary. Any subclasses that add configuration parameters should override `reconfigService` and update those parameters. As with schedulers, because the `AbstractWorker` instance is given directly in the configuration, a reconfigured worker instance must extract its new configuration from another instance of itself.

### User Managers

Since user managers are rarely used, and their purpose is unclear, they are always stopped and re-started on every reconfig. This may change in future versions.

### Status Receivers

At every reconfig, all status listeners are stopped, and new versions are started.