For advanced users, Buildbot acts as a framework supporting a customized build application. For the most part, such configurations consist of subclasses set up for use in a regular Buildbot configuration file.

This chapter describes some of the more common idioms in advanced Buildbot configurations.

At the moment, this chapter is an unordered set of suggestions; if you'd like to clean it up, fork the project on GitHub and get started!

Programmatic Configuration Generation

Bearing in mind that master.cfg is a Python file, large configurations can be shortened considerably by judicious use of Python loops. For example, the following will generate a builder for each of a range of supported versions of Python:

from buildbot.plugins import util, steps

pythons = ['python2.4', 'python2.5', 'python2.6', 'python2.7',
           'python3.2', 'python3.3']

pytest_slaves = ["slave%s" % n for n in range(10)]

for python in pythons:
    f = util.BuildFactory()
    f.addStep(steps.ShellCommand(command=[python, '']))
            name="test-%s" % python,

Merge Request Functions

The logic Buildbot uses to decide which build request can be merged can be customized by providing a Python function (a callable) instead of True or False described in Merging Build Requests.

The callable will be invoked with three positional arguments: a Builder object and two BuildRequest objects. It should return true if the requests can be merged, and False otherwise. For example:

def mergeRequests(builder, req1, req2):
    "any requests with the same branch can be merged"
    return req1.source.branch == req2.source.branch

c['mergeRequests'] = mergeRequests

In many cases, the details of the SourceStamps and BuildRequests are important. In this example, only BuildRequests with the same "reason" are merged; thus developers forcing builds for different reasons will see distinct builds. Note the use of the canBeMergedWith method to access the source stamp compatibility algorithm.

def mergeRequests(builder, req1, req2):
    if req1.source.canBeMergedWith(req2.source) and req1.reason == req2.reason:
       return True
    return False

c['mergeRequests'] = mergeRequests

If it's necessary to perform some extended operation to determine whether two requests can be merged, then the mergeRequests callable may return its result via Deferred. Note, however, that the number of invocations of the callable is proportional to the square of the request queue length, so a long-running callable may cause undesirable delays when the queue length grows. For example:

def mergeRequests(builder, req1, req2):
    d = defer.gatherResults([

    def process(info1, info2):
        return info1 == info2

    return d

c['mergeRequests'] = mergeRequests

Builder Priority Functions

The prioritizeBuilders configuration key specifies a function which is called with two arguments: a BuildMaster and a list of Builder objects. It should return a list of the same Builder objects, in the desired order. It may also remove items from the list if builds should not be started on those builders. If necessary, this function can return its results via a Deferred (it is called with maybeDeferred).

A simple prioritizeBuilders implementation might look like this:

def prioritizeBuilders(buildmaster, builders):
    """Prioritize builders.  'finalRelease' builds have the highest
    priority, so they should be built before running tests, or
    creating builds."""
    builderPriorities = {
        "finalRelease": 0,
        "test": 1,
        "build": 2,
    builders.sort(key=lambda b: builderPriorities.get(, 0))
    return builders

c['prioritizeBuilders'] = prioritizeBuilders

Build Priority Functions

When a builder has multiple pending build requests, it uses a nextBuild function to decide which build it should start first. This function is given two parameters: the Builder, and a list of BuildRequest objects representing pending build requests.

A simple function to prioritize release builds over other builds might look like this:

def nextBuild(bldr, requests):
    for r in requests:
        if r.source.branch == 'release':
            return r
    return requests[0]

If some non-immediate result must be calculated, the nextBuild function can also return a Deferred:

def nextBuild(bldr, requests):
    d = get_request_priorities(requests)

    def pick(priorities):
        if requests:
            return sorted(zip(priorities, requests))[0][1]

    return d

The nextBuild function is passed as parameter to BuilderConfig:

... BuilderConfig(..., nextBuild=nextBuild, ...) ...

Customizing SVNPoller

Each source file that is tracked by a Subversion repository has a fully-qualified SVN URL in the following form: (REPOURL)(PROJECT-plus-BRANCH)(FILEPATH). When you create the SVNPoller, you give it a svnurl value that includes all of the REPOURL and possibly some portion of the PROJECT-plus-BRANCH string. The SVNPoller is responsible for producing Changes that contain a branch name and a FILEPATH (which is relative to the top of a checked-out tree). The details of how these strings are split up depend upon how your repository names its branches.


One common layout is to have all the various projects that share a repository get a single top-level directory each, with branches, tags, and trunk subdirectories:


To set up a SVNPoller that watches the Amanda trunk (and nothing else), we would use the following, using the default split_file:

from buildbot.plugins import changes

c['change_source'] = changes.SVNPoller(

In this case, every Change that our SVNPoller produces will have its branch attribute set to None, to indicate that the Change is on the trunk. No other sub-projects or branches will be tracked.

If we want our ChangeSource to follow multiple branches, we have to do two things. First we have to change our svnurl= argument to watch more than just amanda/trunk. We will set it to amanda so that we'll see both the trunk and all the branches. Second, we have to tell SVNPoller how to split the ({PROJECT-plus-BRANCH})({FILEPATH}) strings it gets from the repository out into ({BRANCH}) and ({FILEPATH})`.

We do the latter by providing a split_file function. This function is responsible for splitting something like branches/3_3/common-src/amanda.h into branch='branches/3_3' and filepath='common-src/amanda.h'. The function is always given a string that names a file relative to the subdirectory pointed to by the SVNPoller's svnurl= argument. It is expected to return a dictionary with at least the path key. The splitter may optionally set branch, project and repository. For backwards compatibility it may return a tuple of (branchname, path). It may also return None to indicate that the file is of no interest.


The function should return branches/3_3 rather than just 3_3 because the SVN checkout step, will append the branch name to the baseURL, which requires that we keep the branches component in there. Other VC schemes use a different approach towards branches and may not require this artifact.

If your repository uses this same {PROJECT}/{BRANCH}/{FILEPATH} naming scheme, the following function will work:

def split_file_branches(path):
    pieces = path.split('/')
    if len(pieces) > 1 and pieces[0] == 'trunk':
        return (None, '/'.join(pieces[1:]))
    elif len(pieces) > 2 and pieces[0] == 'branches':
        return ('/'.join(pieces[0:2]),
        return None

In fact, this is the definition of the provided split_file_branches function. So to have our Twisted-watching SVNPoller follow multiple branches, we would use this:

from buildbot.plugins import changes, util

c['change_source'] = changes.SVNPoller("svn://",

Changes for all sorts of branches (with names like "branches/1.5.x", and None to indicate the trunk) will be delivered to the Schedulers. Each Scheduler is then free to use or ignore each branch as it sees fit.

If you have multiple projects in the same repository your split function can attach a project name to the Change to help the Scheduler filter out unwanted changes:

from buildbot.plugins import util

def split_file_projects_branches(path):
    if not "/" in path:
        return None
    project, path = path.split("/", 1)
    f = util.svn.split_file_branches(path)
    if f:
        info = dict(project=project, path=f[1])
        if f[0]:
            info['branch'] = f[0]
        return info
    return f

Again, this is provided by default. To use it you would do this:

from buildbot.plugins import changes, util

c['change_source'] = changes.SVNPoller(

Note here that we are monitoring at the root of the repository, and that within that repository is a amanda subdirectory which in turn has trunk and branches. It is that amanda subdirectory whose name becomes the project field of the Change.


Another common way to organize a Subversion repository is to put the branch name at the top, and the projects underneath. This is especially frequent when there are a number of related sub-projects that all get released in a group.

For example, hosts a project named Nevow as well as one named Quotient. In a checked-out Nevow tree there is a directory named formless that contains a Python source file named This repository is accessible via webdav (and thus uses an http: scheme) through the hostname. There are many branches in this repository, and they use a ({BRANCHNAME})/({PROJECT}) naming policy.

The fully-qualified SVN URL for the trunk version of is The 1.5.x branch version of this file would have a URL of The whole Nevow trunk would be checked out with, while the Quotient trunk would be checked out using

Now suppose we want to have an SVNPoller that only cares about the Nevow trunk. This case looks just like the {PROJECT}/{BRANCH} layout described earlier:

from buildbot.plugins import changes

c['change_source'] = changes.SVNPoller("")

But what happens when we want to track multiple Nevow branches? We have to point our svnurl= high enough to see all those branches, but we also don't want to include Quotient changes (since we're only building Nevow). To accomplish this, we must rely upon the split_file function to help us tell the difference between files that belong to Nevow and those that belong to Quotient, as well as figuring out which branch each one is on.

from buildbot.plugins import changes, util

c['change_source'] = changes.SVNPoller("",

The my_file_splitter function will be called with repository-relative pathnames like:

This is a Nevow file, on the trunk. We want the Change that includes this to see a filename of formless/, and a branch of None
This is a Nevow file, on a branch. We want to get branch='branches/1.5.x' and filename='formless/'.
This is a Quotient file, so we want to ignore it by having my_file_splitter return None.
This is also a Quotient file, which should be ignored.

The following definition for my_file_splitter will do the job:

def my_file_splitter(path):
    pieces = path.split('/')
    if pieces[0] == 'trunk':
        branch = None
        pieces.pop(0)   # remove 'trunk'
    elif pieces[0] == 'branches':
        pieces.pop(0)   # remove 'branches'
        # grab branch name
        branch = 'branches/' + pieces.pop(0)
        return None     # something weird
    projectname = pieces.pop(0)
    if projectname != 'Nevow':
        return None     # wrong project
    return dict(branch=branch, path='/'.join(pieces))

If you later decide you want to get changes for Quotient as well you could replace the last 3 lines with simply:

return dict(project=projectname, branch=branch, path='/'.join(pieces))

Writing Change Sources

For some version-control systems, making Buildbot aware of new changes can be a challenge. If the pre-supplied classes in Change Sources are not sufficient, then you will need to write your own.

There are three approaches, one of which is not even a change source. The first option is to write a change source that exposes some service to which the version control system can "push" changes. This can be more complicated, since it requires implementing a new service, but delivers changes to Buildbot immediately on commit.

The second option is often preferable to the first: implement a notification service in an external process (perhaps one that is started directly by the version control system, or by an email server) and delivers changes to Buildbot via PBChangeSource. This section does not describe this particular approach, since it requires no customization within the buildmaster process.

The third option is to write a change source which polls for changes - repeatedly connecting to an external service to check for new changes. This works well in many cases, but can produce a high load on the version control system if polling is too frequent, and can take too long to notice changes if the polling is not frequent enough.

Writing a Notification-based Change Source

class buildbot.changes.base.ChangeSource

A custom change source must implement buildbot.interfaces.IChangeSource.

The easiest way to do this is to subclass buildbot.changes.base.ChangeSource, implementing the describe method to describe the instance. ChangeSource is a Twisted service, so you will need to implement the startService and stopService methods to control the means by which your change source receives notifications.

When the class does receive a change, it should call self.master.addChange(..) to submit it to the buildmaster. This method shares the same parameters as master.db.changes.addChange, so consult the API documentation for that function for details on the available arguments.

You will probably also want to set compare_attrs to the list of object attributes which Buildbot will use to compare one change source to another when reconfiguring. During reconfiguration, if the new change source is different from the old, then the old will be stopped and the new started.

Writing a Change Poller

class buildbot.changes.base.PollingChangeSource

Polling is a very common means of seeking changes, so Buildbot supplies a utility parent class to make it easier. A poller should subclass buildbot.changes.base.PollingChangeSource, which is a subclass of ChangeSource. This subclass implements the Service methods, and causes the poll method to be called every self.pollInterval seconds. This method should return a Deferred to signal its completion.

Aside from the service methods, the other concerns in the previous section apply here, too.

Writing a New Latent Buildslave Implementation

Writing a new latent buildslave should only require subclassing buildbot.buildslave.AbstractLatentBuildSlave and implementing start_instance and stop_instance.

def start_instance(self):
    # responsible for starting instance that will try to connect with this
    # master. Should return deferred. Problems should use an errback. The
    # callback value can be None, or can be an iterable of short strings to
    # include in the "substantiate success" status message, such as
    # identifying the instance that started.
    raise NotImplementedError

def stop_instance(self, fast=False):
    # responsible for shutting down instance. Return a deferred. If `fast`,
    # we're trying to shut the master down, so callback as soon as is safe.
    # Callback value is ignored.
    raise NotImplementedError

See buildbot.ec2buildslave.EC2LatentBuildSlave for an example, or see the test example buildbot.test_slaves.FakeLatentBuildSlave.

Custom Build Classes

The standard BuildFactory object creates Build objects by default. These Builds will each execute a collection of BuildSteps in a fixed sequence. Each step can affect the results of the build, but in general there is little intelligence to tie the different steps together.

By setting the factory's buildClass attribute to a different class, you can instantiate a different build class. This might be useful, for example, to create a build class that dynamically determines which steps to run. The skeleton of such a project would look like:

class DynamicBuild(Build):
    # override some methods

f = util.BuildFactory()
f.buildClass = DynamicBuild

Factory Workdir Functions

It is sometimes helpful to have a build's workdir determined at runtime based on the parameters of the build. To accomplish this, set the workdir attribute of the build factory to a callable. That callable will be invoked with the SourceStamp for the build, and should return the appropriate workdir. Note that the value must be returned immediately - Deferreds are not supported.

This can be useful, for example, in scenarios with multiple repositories submitting changes to BuildBot. In this case you likely will want to have a dedicated workdir per repository, since otherwise a sourcing step with mode = "update" will fail as a workdir with a working copy of repository A can't be "updated" for changes from a repository B. Here is an example how you can achieve workdir-per-repo:

def workdir(source_stamp):
    return hashlib.md5 (source_stamp.repository).hexdigest()[:8]

build_factory = util.BuildFactory()
build_factory.workdir = workdir

# ...
builders.append ({'name': 'mybuilder',
                  'slavename': 'myslave',
                  'builddir': 'mybuilder',
                  'factory': build_factory})

The end result is a set of workdirs like

Repo1 => <buildslave-base>/mybuilder/a78890ba
Repo2 => <buildslave-base>/mybuilder/0823ba88

You could make the workdir function compute other paths, based on parts of the repo URL in the sourcestamp, or lookup in a lookup table based on repo URL. As long as there is a permanent 1:1 mapping between repos and workdir, this will work.

Writing New BuildSteps


Buildbot is transitioning to a new, simpler style for writing custom steps. See New-Style Build Steps for details. This section documents new-style steps exclusively, although old-style steps are still supported.

While it is a good idea to keep your build process self-contained in the source code tree, sometimes it is convenient to put more intelligence into your Buildbot configuration. One way to do this is to write a custom BuildStep. Once written, this Step can be used in the master.cfg file.

The best reason for writing a custom BuildStep is to better parse the results of the command being run. For example, a BuildStep that knows about JUnit could look at the logfiles to determine which tests had been run, how many passed and how many failed, and then report more detailed information than a simple rc==0 -based good/bad decision.

Buildbot has acquired a large fleet of build steps, and sports a number of knobs and hooks to make steps easier to write. This section may seem a bit overwhelming, but most custom steps will only need to apply one or two of the techniques outlined here.

For complete documentation of the build step interfaces, see BuildSteps.

Writing BuildStep Constructors

Build steps act as their own factories, so their constructors are a bit more complex than necessary. The configuration file instantiates a BuildStep object, but the step configuration must be re-used for multiple builds, so Buildbot needs some way to create more steps.

Consider the use of a BuildStep in master.cfg:

f.addStep(MyStep(someopt="stuff", anotheropt=1))

This creates a single instance of class MyStep. However, Buildbot needs a new object each time the step is executed. An instance of BuildStep remembers how it was constructed, and can create copies of itself. When writing a new step class, then, keep in mind are that you cannot do anything "interesting" in the constructor -- limit yourself to checking and storing arguments.

It is customary to call the parent class's constructor with all otherwise-unspecified keyword arguments. Keep a **kwargs argument on the end of your options, and pass that up to the parent class's constructor.

The whole thing looks like this:

class Frobnify(LoggingBuildStep):
    def __init__(self,
        # check
        if frob_how_many is None:
            raise TypeError("Frobnify argument how_many is required")

        # override a parent option
        kwargs['parentOpt'] = 'xyz'

        # call parent
        LoggingBuildStep.__init__(self, **kwargs)

        # set Frobnify attributes
        self.frob_what = frob_what
        self.frob_how_many = how_many
        self.frob_how = frob_how

class FastFrobnify(Frobnify):
    def __init__(self, speed=5, **kwargs):
        Frobnify.__init__(self, **kwargs)
        self.speed = speed

Step Execution Process

A step's execution occurs in its run method. When this method returns (more accurately, when the Deferred it returns fires), the step is complete. The method's result must be an integer, giving the result of the step. Any other output from the step (logfiles, status strings, URLs, etc.) is the responsibility of the run method.

The ShellCommand class implements this run method, and in most cases steps subclassing ShellCommand simply implement some of the subsidiary methods that its run method calls.

Running Commands

To spawn a command in the buildslave, create a RemoteCommand instance in your step's run method and run it with runCommand:

cmd = RemoteCommand(args)
d = self.runCommand(cmd)

The CommandMixin class offers a simple interface to several common slave-side commands.

For the much more common task of running a shell command on the buildslave, use ShellMixin. This class provides a method to handle the myriad constructor arguments related to shell commands, as well as a method to create new RemoteCommand instances. This mixin is the recommended method of implementing custom shell-based steps. The older pattern of subclassing ShellCommand is no longer recommended.

A simple example of a step using the shell mixin is:

class RunCleanup(buildstep.ShellMixin, buildstep.BuildStep):
    def __init__(self, cleanupScript='./', **kwargs):
        self.cleanupScript = cleanupScript
        kwargs = self.setupShellMixin(kwargs, prohibitArgs=['command'])
        buildstep.BuildStep.__init__(self, **kwargs)

    def run(self):
        cmd = yield self.makeRemoteShellCommand(command=[self.cleanupScript])
        yield self.runCommand(cmd)
        if cmd.didFail():
            cmd = yield self.makeRemoteShellCommand(command=[self.cleanupScript, '--force'],
            yield self.runCommand(cmd)

def run(self):
    cmd = RemoteCommand(args)
    log = yield self.addLog('output')
    cmd.useLog(log, closeWhenFinished=True)
    yield self.runCommand(cmd)

Updating Status Strings

Each step can summarize its current status in a very short string. For example, a compile step might display the file being compiled. This information can be helpful users eager to see their build finish.

Similarly, a build has a set of short strings collected from its steps summarizing the overall state of the build. Useful information here might include the number of tests run, but probably not the results of a make clean step.

As a step runs, Buildbot calls its getCurrentSummary method as necessary to get the step's current status. "As necessary" is determined by calls to buildbot.process.buildstep.BuildStep.updateSummary. Your step should call this method every time the status summary may have changed. Buildbot will take care of rate-limiting summary updates.

When the step is complete, Buildbot calls its getResultSummary method to get a final summary of the step along with a summary for the build.

About Logfiles

Each BuildStep has a collection of log files. Each one has a short name, like stdio or warnings. Each log file contains an arbitrary amount of text, usually the contents of some output file generated during a build or test step, or a record of everything that was printed to stdout/stderr during the execution of some command.

Each can contain multiple channels, generally limited to three basic ones: stdout, stderr, and headers. For example, when a shell command runs, it writes a few lines to the headers channel to indicate the exact argv strings being run, which directory the command is being executed in, and the contents of the current environment variables. Then, as the command runs, it adds a lot of stdout and stderr messages. When the command finishes, a final header line is added with the exit code of the process.

Status display plugins can format these different channels in different ways. For example, the web page shows log files as text/html, with header lines in blue text, stdout in black, and stderr in red. A different URL is available which provides a text/plain format, in which stdout and stderr are collapsed together, and header lines are stripped completely. This latter option makes it easy to save the results to a file and run grep or whatever against the output.

Writing Log Files

Most commonly, logfiles come from commands run on the build slave. Internally, these are configured by supplying the RemoteCommand instance with log files via the useLog method:

def run(self):
    log = yield self.addLog('stdio')
    cmd.useLog(log, closeWhenFinished=True, 'stdio')
    yield self.runCommand(cmd)

The name passed to useLog must match that configured in the command. In this case, stdio is the default.

If the log file was already added by another part of the step, it can be retrieved with getLog:

stdioLog = self.getLog('stdio')

Less frequently, some master-side processing produces a log file. If this log file is short and easily stored in memory, this is as simple as a call to addCompleteLog:

def run(self):
    summary = u'\n'.join('%s: %s' % (k, count)
                         for (k, count) in self.lint_results.iteritems())
    yield self.addCompleteLog('summary', summary)

Note that the log contents must be a unicode string.

Longer logfiles can be constructed line-by-line using the add methods of the log file:

def run(self):
    updates = yield self.addLog('updates')
    while True:
        yield updates.addStdout(some_update)

Again, note that the log input must be a unicode string.

Finally, addHTMLLog is similar to addCompleteLog, but the resulting log will be tagged as containing HTML. The web UI will display the contents of the log using the browser.

The logfiles= argument to ShellCommand and its subclasses creates new log files and fills them in realtime by asking the buildslave to watch a actual file on disk. The buildslave will look for additions in the target file and report them back to the BuildStep. These additions will be added to the log file by calling addStdout.

All log files can be used as the source of a LogObserver just like the normal stdio LogFile. In fact, it's possible for one LogObserver to observe a logfile created by another.

Reading Logfiles

For the most part, Buildbot tries to avoid loading the contents of a log file into memory as a single string. For large log files on a busy master, this behavior can quickly consume a great deal of memory.

Instead, steps should implement a LogObserver to examine log files one chunk or line at a time.

For commands which only produce a small quantity of output, RemoteCommand will collect the command's stdout into its stdout attribute if given the collectStdout=True constructor argument.

Adding LogObservers

Most shell commands emit messages to stdout or stderr as they operate, especially if you ask them nicely with a --verbose flag of some sort. They may also write text to a log file while they run. Your BuildStep can watch this output as it arrives, to keep track of how much progress the command has made or to process log output for later summarization.

To accomplish this, you will need to attach a LogObserver to the log. This observer is given all text as it is emitted from the command, and has the opportunity to parse that output incrementally.

There are a number of pre-built LogObserver classes that you can choose from (defined in buildbot.process.buildstep, and of course you can subclass them to add further customization. The LogLineObserver class handles the grunt work of buffering and scanning for end-of-line delimiters, allowing your parser to operate on complete stdout/stderr lines. (Lines longer than a set maximum length are dropped; the maximum defaults to 16384 bytes, but you can change it by calling setMaxLineLength on your LogLineObserver instance. Use sys.maxint for effective infinity.)

For example, let's take a look at the TrialTestCaseCounter, which is used by the Trial step to count test cases as they are run. As Trial executes, it emits lines like the following:

buildbot.test.test_config.ConfigTest.testDebugPassword ... [OK]
buildbot.test.test_config.ConfigTest.testEmpty ... [OK]
buildbot.test.test_config.ConfigTest.testIRC ... [FAIL]
buildbot.test.test_config.ConfigTest.testLocks ... [OK]

When the tests are finished, trial emits a long line of ====== and then some lines which summarize the tests that failed. We want to avoid parsing these trailing lines, because their format is less well-defined than the [OK] lines.

A simple version of the parser for this output looks like this. The full version is in master/buildbot/steps/

from buildbot.plugins import util

class TrialTestCaseCounter(util.LogLineObserver):
    _line_re = re.compile(r'^([\w\.]+) \.\.\. \[([^\]]+)\]$')
    numTests = 0
    finished = False

    def outLineReceived(self, line):
        if self.finished:
        if line.startswith("=" * 40):
            self.finished = True

        m =
        if m:
            testname, result = m.groups()
            self.numTests += 1
            self.step.setProgress('tests', self.numTests)

This parser only pays attention to stdout, since that's where trial writes the progress lines. It has a mode flag named finished to ignore everything after the ==== marker, and a scary-looking regular expression to match each line while hopefully ignoring other messages that might get displayed as the test runs.

Each time it identifies a test has been completed, it increments its counter and delivers the new progress value to the step with self.step.setProgress. This helps Buildbot to determine the ETA for the step.

To connect this parser into the Trial build step, Trial.__init__ ends with the following clause:

# this counter will feed Progress along the 'test cases' metric
counter = TrialTestCaseCounter()
self.addLogObserver('stdio', counter)
self.progressMetrics += ('tests',)

This creates a TrialTestCaseCounter and tells the step that the counter wants to watch the stdio log. The observer is automatically given a reference to the step in its step attribute.

Using Properties

In custom BuildSteps, you can get and set the build properties with the getProperty and setProperty methods. Each takes a string for the name of the property, and returns or accepts an arbitrary JSON-able (lists, dicts, strings, and numbers) object. For example:

class MakeTarball(ShellCommand):
    def start(self):
        if self.getProperty("os") == "win":
            self.setCommand([ ... ]) # windows-only command
            self.setCommand([ ... ]) # equivalent for other systems

Remember that properties set in a step may not be available until the next step begins. In particular, any Property or Interpolate instances for the current step are interpolated before the step starts, so they cannot use the value of any properties determined in that step.

Using Statistics

Statistics can be generated for each step, and then summarized across all steps in a build. For example, a test step might set its warnings statistic to the number of warnings observed. The build could then sum the warnings on all steps to get a total number of warnings.

Statistics are set and retrieved with the setStatistic and:py:meth:~buildbot.process.buildstep.BuildStep.getStatistic methods. The hasStatistic method determines whether a statistic exists.

The Build method getSummaryStatistic can be used to aggregate over all steps in a Build.

BuildStep URLs

Each BuildStep has a collection of links. Each has a name and a target URL. The web display displays clickable links for each link, making them a useful way to point to extra information about a step. For example, a step that uploads a build result to an external service might include a link to the uploaded flie.

To set one of these links, the BuildStep should call the addURL method with the name of the link and the target URL. Multiple URLs can be set. For example:

def run(self):
    ... # create and upload report to coverage server
    url = '' % reportname
    yield self.addURL('coverage', url)

Discovering files

When implementing a BuildStep it may be necessary to know about files that are created during the build. There are a few slave commands that can be used to find files on the slave and test for the existence (and type) of files and directories.

The slave provides the following file-discovery related commands:

  • stat calls os.stat for a file in the slave's build directory. This can be used to check if a known file exists and whether it is a regular file, directory or symbolic link.
  • listdir calls os.listdir for a directory on the slave. It can be used to obtain a list of files that are present in a directory on the slave.
  • glob calls glob.glob on the slave, with a given shell-style pattern containing wildcards.

For example, we could use stat to check if a given path exists and contains *.pyc files. If the path does not exist (or anything fails) we mark the step as failed; if the path exists but is not a directory, we mark the step as having "warnings".

from buildbot.plugins import steps, util
from buildbot.interfaces import BuildSlaveToOldError
import stat

class MyBuildStep(steps.BuildStep):

    def __init__(self, dirname, **kwargs):
        steps.BuildStep.__init__(self, **kwargs)
        self.dirname = dirname

    def start(self):
        # make sure the slave knows about stat
        slavever = (self.slaveVersion('stat'),
        if not all(slavever):
            raise BuildSlaveToOldError('need stat and glob')

        cmd = util.RemoteCommand('stat', {'file': self.dirname})

        d = self.runCommand(cmd)
        d.addCallback(lambda res: self.evaluateStat(cmd))
        return d

    def evaluateStat(self, cmd):
        if cmd.didFail():
            self.step_status.setText(["File not found."])
        s = cmd.updates["stat"][-1]
        if not stat.S_ISDIR(s[stat.ST_MODE]):
            self.step_status.setText(["'tis not a directory"])

        cmd = util.RemoteCommand('glob', {'glob': self.dirname + '/*.pyc'})

        d = self.runCommand(cmd)
        d.addCallback(lambda res: self.evaluateGlob(cmd))
        return d

    def evaluateGlob(self, cmd):
        if cmd.didFail():
            self.step_status.setText(["Glob failed."])
        files = cmd.updates["files"][-1]
        if len(files):
            self.step_status.setText(["Found pycs"]+files)
            self.step_status.setText(["No pycs found"])

For more information on the available commands, see Master-Slave API.

Writing New Status Plugins

Each status plugin is an object which provides the twisted.application.service.IService interface, which creates a tree of Services with the buildmaster at the top [not strictly true]. The status plugins are all children of an object which implements buildbot.interfaces.IStatus, the main status object. From this object, the plugin can retrieve anything it wants about current and past builds. It can also subscribe to hear about new and upcoming builds.

Status plugins which only react to human queries (like the Waterfall display) never need to subscribe to anything: they are idle until someone asks a question, then wake up and extract the information they need to answer it, then they go back to sleep. Plugins which need to act spontaneously when builds complete (like the MailNotifier plugin) need to subscribe to hear about new builds.

If the status plugin needs to run network services (like the HTTP server used by the Waterfall plugin), they can be attached as Service children of the plugin itself, using the IServiceCollection interface.

A Somewhat Whimsical Example (or "It's now customized, how do I deploy it?")

Let's say that we've got some snazzy new unit-test framework called Framboozle. It's the hottest thing since sliced bread. It slices, it dices, it runs unit tests like there's no tomorrow. Plus if your unit tests fail, you can use its name for a Web 2.1 startup company, make millions of dollars, and hire engineers to fix the bugs for you, while you spend your afternoons lazily hang-gliding along a scenic pacific beach, blissfully unconcerned about the state of your tests. [1]

To run a Framboozle-enabled test suite, you just run the 'framboozler' command from the top of your source code tree. The 'framboozler' command emits a bunch of stuff to stdout, but the most interesting bit is that it emits the line "FNURRRGH!" every time it finishes running a test case You'd like to have a test-case counting LogObserver that watches for these lines and counts them, because counting them will help the buildbot more accurately calculate how long the build will take, and this will let you know exactly how long you can sneak out of the office for your hang-gliding lessons without anyone noticing that you're gone.

This will involve writing a new BuildStep (probably named "Framboozle") which inherits from ShellCommand. The BuildStep class definition itself will look something like this:

from buildbot.plugins import steps, util

class FNURRRGHCounter(util.LogLineObserver):
    numTests = 0
    def outLineReceived(self, line):
        if "FNURRRGH!" in line:
            self.numTests += 1
            self.step.setProgress('tests', self.numTests)

class Framboozle(steps.ShellCommand):
    command = ["framboozler"]

    def __init__(self, **kwargs):
        steps.ShellCommand.__init__(self, **kwargs)     # always upcall!
        counter = FNURRRGHCounter()
        self.addLogObserver('stdio', counter)
        self.progressMetrics += ('tests',)

So that's the code that we want to wind up using. How do we actually deploy it?

You have a number of different options:

Inclusion in the master.cfg file

The simplest technique is to simply put the step class definitions in your master.cfg file, somewhere before the BuildFactory definition where you actually use it in a clause like:

from buildbot.plugins import steps, util

f = util.BuildFactory()

Remember that master.cfg is just a Python program with one job: populating the BuildmasterConfig dictionary. And Python programs are allowed to define as many classes as they like. So you can define classes and use them in the same file, just as long as the class is defined before some other code tries to use it.

This is easy, and it keeps the point of definition very close to the point of use, and whoever replaces you after that unfortunate hang-gliding accident will appreciate being able to easily figure out what the heck this stupid "Framboozle" step is doing anyways. The downside is that every time you reload the config file, the Framboozle class will get redefined, which means that the buildmaster will think that you've reconfigured all the Builders that use it, even though nothing changed. Bleh.

Python file somewhere on the system

Instead, we can put this code in a separate file, and import it into the master.cfg file just like we would the normal buildsteps like ShellCommand and SVN.

Create a directory named ~/lib/python, put the step class definitions in ~/lib/python/, and run your buildmaster using:

PYTHONPATH=~/lib/python buildbot start MASTERDIR

or use the Makefile.buildbot to control the way buildbot start works. Or add something like this to something like your ~/.bashrc or ~/.bash_profile or ~/.cshrc:

export PYTHONPATH=~/lib/python

Once we've done this, our master.cfg can look like:

from buildbot.plugins import steps, util
from framboozle import Framboozle

f = util.BuildFactory()


from buildbot.plugins import steps, util
import framboozle

f = util.BuildFactory()

(check out the Python docs for details about how import and from A import B work).

What we've done here is to tell Python that every time it handles an "import" statement for some named module, it should look in our ~/lib/python/ for that module before it looks anywhere else. After our directories, it will try in a bunch of standard directories too (including the one where buildbot is installed). By setting the PYTHONPATH environment variable, you can add directories to the front of this search list.

Python knows that once it "import"s a file, it doesn't need to re-import it again. This means that reconfiguring the buildmaster (with buildbot reconfig, for example) won't make it think the Framboozle class has changed every time, so the Builders that use it will not be spuriously restarted. On the other hand, you either have to start your buildmaster in a slightly weird way, or you have to modify your environment to set the PYTHONPATH variable.

Install this code into a standard Python library directory

Find out what your Python's standard include path is by asking it:

80:warner@luther% python
Python 2.4.4c0 (#2, Oct  2 2006, 00:57:46)
[GCC 4.1.2 20060928 (prerelease) (Debian 4.1.1-15)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> import pprint
>>> pprint.pprint(sys.path)

In this case, putting the code into /usr/local/lib/python2.4/site-packages/ would work just fine. We can use the same master.cfg import framboozle statement as in Option 2. By putting it in a standard include directory (instead of the decidedly non-standard ~/lib/python), we don't even have to set PYTHONPATH to anything special. The downside is that you probably have to be root to write to one of those standard include directories.

Distribute a Buildbot Plug-In

First of all, you must prepare a Python package (if you do not know what that is, please check How to package Buildbot plugins, where you can find a couple of pointers to tutorials).

When you have a package, you will have a special file called This file needs to be updated to include a pointer to your new step:

    entry_points = {
        'buildbot.steps': [
            'Framboozle = framboozle:Framboozle'


  • buildbot.steps is the kind of plugin you offer (more information about possible kinds you can find in How to package Buildbot plugins)

  • framboozle:Framboozle consists of two parts: framboozle is the name of the python module where to look for Framboozle class, which implements the plugin

  • Framboozle is the name of the plugin.

    This will allow users of your plugin to use it just like any other Buildbot plugins:

    from buildbot.plugins import steps
    ... steps.Framboozle ...

Now you can upload it to PyPI where other people can download it from and use in their build systems. Once again, the information about how to prepare and upload a package to PyPI can be found in tutorials listed in How to package Buildbot plugins.

Submit the code for inclusion in the Buildbot distribution

Make a fork of buildbot on or post a patch in a bug at In either case, post a note about your patch to the mailing list, so others can provide feedback and, eventually, commit it.

from buildbot.plugins import steps, util

f = util.BuildFactory()

And then you don't even have to install anywhere on your system, since it will ship with Buildbot. You don't have to be root, you don't have to set PYTHONPATH. But you do have to make a good case for Framboozle being worth going into the main distribution, you'll probably have to provide docs and some unit test cases, you'll need to figure out what kind of beer the author likes (IPA's and Stouts for Dustin), and then you'll have to wait until the next release. But in some environments, all this is easier than getting root on your buildmaster box, so the tradeoffs may actually be worth it.


Putting the code in master.cfg (1) makes it available to that buildmaster instance. Putting it in a file in a personal library directory (2) makes it available for any buildmasters you might be running. Putting it in a file in a system-wide shared library directory (3) makes it available for any buildmasters that anyone on that system might be running. Getting it into the buildbot's upstream repository (4) makes it available for any buildmasters that anyone in the world might be running. It's all a matter of how widely you want to deploy that new class.

[1] is still available. Remember, I get 10% :).