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 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:


The title of this buildmaster, from title.


The URL corresponding to the title, from titleURL.


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


The current change horizon, from changeHorizon.


The current event horizon, from eventHorizon.


The current log horizon, from logHorizon.


The current build horizon, from buildHorizon.


The current log compression limit, from logCompressionLimit.


The current log compression method, from logCompressionMethod.


The current log maximum size, from logMaxSize.


The current log maximum size, from logMaxTailSize.


A Properties instance containing global properties, from properties.


A callable, or True or False, describing how to merge requests; from mergeRequests.


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


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


The per-protocol port specification for slave connections. Based on protocols.


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


The password for the debug client, or None; from debugPassword.


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

The remaining attributes contain compound configuration structures, usually dictionaries:


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


Database specification, a dictionary with keys db_url and db_poll_interval. It is safe to assume that both keys are present.


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


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).


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


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


The list of BuildSlave instances from slaves.


The list of IChangeSource providers from change_source.


The list of IStatusReceiver providers from status.


The list of user managers providers from user_managers.

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

classmethod loadConfig(basedir, filename)
  • basedir (string) -- directory to which config is relative
  • filename (string) -- the configuration file to load

ConfigErrors if any errors occur


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.

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

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 and 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.


The builder's name.


The builder's factory.


The builder's slave names (a list, regardless of whether the names were specified with slavename or slavenames).


The builder's builddir.


The builder's slave-side builddir.


The builder's category.


The builder's nextSlave callable.


The builder's nextBuild callable.


The builder's canStartBuild callable.


The builder's locks.


The builder's environmnet variables.


The builder's properties, as a dictionary.


The builder's mergeRequests callable.


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

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, slaves, schedulers, build steps, and so on.

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 all config errors can be reported, rather than just the first.

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.


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

Parameters:msg (string) -- the message to add

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


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.


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 reconfigService method.

class buildbot.config.ReconfigurableServiceMixin
Parameters:new_config (MasterConfig) -- new master configuration

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.


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 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 which do not support reconfiguration will be stopped, and the new scheduler started, when their configuration changes.

If, during a reconfiguration, a new and old scheduler's fully qualified class names differ, then the old class will be stopped and the new class 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 BaseScheduler instances directly in the configuration file, a reconfigured scheduler must extract its new configuration information from another instance of itself. BaseScheduler implements a helper method, findNewSchedulerInstance, which will return the new instance of the scheduler in the given MasterConfig object.

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.


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

This method takes care of the basic slave 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 AbstractBuildSlave instance is given directly in the configuration, on reconfig instances must extract the configuration from a new instance. The findNewSlaveInstance method can be used to find the new instance.

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 figure versions.

Status Receivers

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