Buildslaves

The slaves configuration key specifies a list of known buildslaves. In the common case, each buildslave is defined by an instance of the BuildSlave class. It represents a standard, manually started machine that will try to connect to the buildbot master as a slave. Buildbot also supports "on-demand", or latent, buildslaves, which allow buildbot to dynamically start and stop buildslave instances.

Defining Buildslaves

A BuildSlave instance is created with a slavename and a slavepassword. These are the same two values that need to be provided to the buildslave administrator when they create the buildslave.

The slavename must be unique, of course. The password exists to prevent evildoers from interfering with the buildbot by inserting their own (broken) buildslaves into the system and thus displacing the real ones.

Buildslaves with an unrecognized slavename or a non-matching password will be rejected when they attempt to connect, and a message describing the problem will be written to the log file (see Logfiles).

A configuration for two slaves would look like:

from buildbot.buildslave import BuildSlave
c['slaves'] = [
    BuildSlave('bot-solaris', 'solarispasswd'),
    BuildSlave('bot-bsd', 'bsdpasswd'),
]

BuildSlave Options

BuildSlave objects can also be created with an optional properties argument, a dictionary specifying properties that will be available to any builds performed on this slave. For example:

c['slaves'] = [
    BuildSlave('bot-solaris', 'solarispasswd',
                properties={ 'os':'solaris' }),
]

The BuildSlave constructor can also take an optional max_builds parameter to limit the number of builds that it will execute simultaneously:

c['slaves'] = [
    BuildSlave("bot-linux", "linuxpassword", max_builds=2)
]

Master-Slave TCP Keepalive

By default, the buildmaster sends a simple, non-blocking message to each slave every hour. These keepalives ensure that traffic is flowing over the underlying TCP connection, allowing the system's network stack to detect any problems before a build is started.

The interval can be modified by specifying the interval in seconds using the keepalive_interval parameter of BuildSlave:

c['slaves'] = [
    BuildSlave('bot-linux', 'linuxpasswd',
                keepalive_interval=3600),
]

The interval can be set to None to disable this functionality altogether.

When Buildslaves Go Missing

Sometimes, the buildslaves go away. One very common reason for this is when the buildslave process is started once (manually) and left running, but then later the machine reboots and the process is not automatically restarted.

If you'd like to have the administrator of the buildslave (or other people) be notified by email when the buildslave has been missing for too long, just add the notify_on_missing= argument to the BuildSlave definition. This value can be a single email address, or a list of addresses:

c['slaves'] = [
    BuildSlave('bot-solaris', 'solarispasswd',
                notify_on_missing="bob@example.com"),
]

By default, this will send email when the buildslave has been disconnected for more than one hour. Only one email per connection-loss event will be sent. To change the timeout, use missing_timeout= and give it a number of seconds (the default is 3600).

You can have the buildmaster send email to multiple recipients: just provide a list of addresses instead of a single one:

c['slaves'] = [
    BuildSlave('bot-solaris', 'solarispasswd',
                notify_on_missing=["bob@example.com",
                                    "alice@example.org"],
                missing_timeout=300, # notify after 5 minutes
    ),
]

The email sent this way will use a MailNotifier (see MailNotifier) status target, if one is configured. This provides a way for you to control the from address of the email, as well as the relayhost (aka smarthost) to use as an SMTP server. If no MailNotifier is configured on this buildmaster, the buildslave-missing emails will be sent using a default configuration.

Note that if you want to have a MailNotifier for buildslave-missing emails but not for regular build emails, just create one with builders=[], as follows:

from buildbot.status import mail
m = mail.MailNotifier(fromaddr="buildbot@localhost", builders=[],
                      relayhost="smtp.example.org")
c['status'].append(m)

from buildbot.buildslave import BuildSlave
c['slaves'] = [
        BuildSlave('bot-solaris', 'solarispasswd',
                    notify_on_missing="bob@example.com"),
]

Latent Buildslaves

The standard buildbot model has slaves started manually. The previous section described how to configure the master for this approach.

Another approach is to let the buildbot master start slaves when builds are ready, on-demand. Thanks to services such as Amazon Web Services' Elastic Compute Cloud ("AWS EC2"), this is relatively easy to set up, and can be very useful for some situations.

The buildslaves that are started on-demand are called "latent" buildslaves. As of this writing, buildbot ships with an abstract base class for building latent buildslaves, and a concrete implementation for AWS EC2 and for libvirt.

Common Options

The following options are available for all latent buildslaves.

build_wait_timeout
This option allows you to specify how long a latent slave should wait after a build for another build before it shuts down. It defaults to 10 minutes. If this is set to 0 then the slave will be shut down immediately. If it is less than 0 it will never automatically shutdown.

Amazon Web Services Elastic Compute Cloud ("AWS EC2")

EC2 is a web service that allows you to start virtual machines in an Amazon data center. Please see their website for details, including costs. Using the AWS EC2 latent buildslaves involves getting an EC2 account with AWS and setting up payment; customizing one or more EC2 machine images ("AMIs") on your desired operating system(s) and publishing them (privately if needed); and configuring the buildbot master to know how to start your customized images for "substantiating" your latent slaves.

Get an AWS EC2 Account

To start off, to use the AWS EC2 latent buildslave, you need to get an AWS developer account and sign up for EC2. Although Amazon often changes this process, these instructions should help you get started:

  1. Go to http://aws.amazon.com/ and click to "Sign Up Now" for an AWS account.
  2. Once you are logged into your account, you need to sign up for EC2. Instructions for how to do this have changed over time because Amazon changes their website, so the best advice is to hunt for it. After signing up for EC2, it may say it wants you to upload an x.509 cert. You will need this to create images (see below) but it is not technically necessary for the buildbot master configuration.
  3. You must enter a valid credit card before you will be able to use EC2. Do that under 'Payment Method'.
  4. Make sure you're signed up for EC2 by going to 'Your Account'->'Account Activity' and verifying EC2 is listed.

Create an AMI

Now you need to create an AMI and configure the master. You may need to run through this cycle a few times to get it working, but these instructions should get you started.

Creating an AMI is out of the scope of this document. The EC2 Getting Started Guide is a good resource for this task. Here are a few additional hints.

  • When an instance of the image starts, it needs to automatically start a buildbot slave that connects to your master (to create a buildbot slave, Creating a buildslave; to make a daemon, Launching the daemons).
  • You may want to make an instance of the buildbot slave, configure it as a standard buildslave in the master (i.e., not as a latent slave), and test and debug it that way before you turn it into an AMI and convert to a latent slave in the master.

Configure the Master with an EC2LatentBuildSlave

Now let's assume you have an AMI that should work with the EC2LatentBuildSlave. It's now time to set up your buildbot master configuration.

You will need some information from your AWS account: the Access Key Id and the Secret Access Key. If you've built the AMI yourself, you probably already are familiar with these values. If you have not, and someone has given you access to an AMI, these hints may help you find the necessary values:

  • While logged into your AWS account, find the "Access Identifiers" link (either on the left, or via "Your Account" -> "Access Identifiers".
  • On the page, you'll see alphanumeric values for "Your Access Key Id:" and "Your Secret Access Key:". Make a note of these. Later on, we'll call the first one your identifier and the second one your secret_identifier.

When creating an EC2LatentBuildSlave in the buildbot master configuration, the first three arguments are required. The name and password are the first two arguments, and work the same as with normal buildslaves. The next argument specifies the type of the EC2 virtual machine (available options as of this writing include m1.small, m1.large, m1.xlarge, c1.medium, and c1.xlarge; see the EC2 documentation for descriptions of these machines).

Here is the simplest example of configuring an EC2 latent buildslave. It specifies all necessary remaining values explicitly in the instantiation.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   ami='ami-12345',
                                   identifier='publickey',
                                   secret_identifier='privatekey'
                                   )]

The ami argument specifies the AMI that the master should start. The identifier argument specifies the AWS Access Key Id, and the secret_identifier specifies the AWS Secret Access Key. Both the AMI and the account information can be specified in alternate ways.

Note

Whoever has your identifier and secret_identifier values can request AWS work charged to your account, so these values need to be carefully protected. Another way to specify these access keys is to put them in a separate file. You can then make the access privileges stricter for this separate file, and potentially let more people read your main configuration file.

By default, you can make an .ec2 directory in the home folder of the user running the buildbot master. In that directory, create a file called aws_id. The first line of that file should be your access key id; the second line should be your secret access key id. Then you can instantiate the build slave as follows.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   ami='ami-12345')]

If you want to put the key information in another file, use the aws_id_file_path initialization argument.

Previous examples used a particular AMI. If the Buildbot master will be deployed in a process-controlled environment, it may be convenient to specify the AMI more flexibly. Rather than specifying an individual AMI, specify one or two AMI filters.

In all cases, the AMI that sorts last by its location (the S3 bucket and manifest name) will be preferred.

One available filter is to specify the acceptable AMI owners, by AWS account number (the 12 digit number, usually rendered in AWS with hyphens like "1234-5678-9012", should be entered as in integer).

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
bot1 = EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                           valid_ami_owners=[11111111111,
                                             22222222222],
                           identifier='publickey',
                           secret_identifier='privatekey'
                           )

The other available filter is to provide a regular expression string that will be matched against each AMI's location (the S3 bucket and manifest name).

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
bot1 = EC2LatentBuildSlave(
    'bot1', 'sekrit', 'm1.large',
    valid_ami_location_regex=r'buildbot\-.*/image.manifest.xml',
    identifier='publickey', secret_identifier='privatekey')

The regular expression can specify a group, which will be preferred for the sorting. Only the first group is used; subsequent groups are ignored.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
bot1 = EC2LatentBuildSlave(
    'bot1', 'sekrit', 'm1.large',
    valid_ami_location_regex=r'buildbot\-.*\-(.*)/image.manifest.xml',
    identifier='publickey', secret_identifier='privatekey')

If the group can be cast to an integer, it will be. This allows 10 to sort after 1, for instance.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
bot1 = EC2LatentBuildSlave(
    'bot1', 'sekrit', 'm1.large',
    valid_ami_location_regex=r'buildbot\-.*\-(\d+)/image.manifest.xml',
    identifier='publickey', secret_identifier='privatekey')

In addition to using the password as a handshake between the master and the slave, you may want to use a firewall to assert that only machines from a specific IP can connect as slaves. This is possible with AWS EC2 by using the Elastic IP feature. To configure, generate a Elastic IP in AWS, and then specify it in your configuration using the elastic_ip argument.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   'ami-12345',
                                   identifier='publickey',
                                   secret_identifier='privatekey',
                                   elastic_ip='208.77.188.166'
                                   )]

One other way to configure a slave is by settings AWS tags. They can for example be used to have a more restrictive security IAM policy. To get Buildbot to tag the latent slave specify the tag keys and values in your configuration using the tags argument.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   'ami-12345',
                                   identifier='publickey',
                                   secret_identifier='privatekey',
                                   tags={'SomeTag': 'foo'}
                                   )]

The EC2LatentBuildSlave supports all other configuration from the standard BuildSlave. The missing_timeout and notify_on_missing specify how long to wait for an EC2 instance to attach before considering the attempt to have failed, and email addresses to alert, respectively. missing_timeout defaults to 20 minutes.

volumes expects a list of (volume_id, mount_point) tuples to attempt attaching when your instance has been created.

keypair_name and security_name allow you to specify different names for these AWS EC2 values. They both default to latent_buildbot_slave.

Spot instances

If you would prefer to use spot instances for running your builds, you can accomplish that by passing in a True value to the spot_instance parameter to the EC2LatentBuildSlave constructor. Additionally, you may want to specify max_spot_price and price_multiplier in order to limit your builds' budget consumption.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   'ami-12345', region='us-west-2',
                                   identifier='publickey',
                                   secret_identifier='privatekey',
                                   elastic_ip='208.77.188.166',
                                   placement='b', spot_instance=True,
                                   max_spot_price=0.09,
                                   price_multiplier=1.15,
                                   product_description='Linux/UNIX'
                                   )]

This example would attempt to create a m1.large spot instance in the us-west-2b region costing no more than $0.09/hour. The spot prices for 'Linux/UNIX' spot instances in that region over the last 24 hours will be averaged and multiplied by the price_multiplier parameter, then a spot request will be sent to Amazon with the above details.

When a spot request fails

In some cases Amazon may reject a spot request because the spot price, determined by taking the 24-hour average of that availability zone's spot prices for the given product description, is lower than the current price. The optional parameters retry and retry_price_adjustment allow for resubmitting the spot request with an adjusted price. If the spot request continues to fail, and the number of attempts exceeds the value of the retry parameter, an error message will be logged.

from buildbot.buildslave.ec2 import EC2LatentBuildSlave
c['slaves'] = [EC2LatentBuildSlave('bot1', 'sekrit', 'm1.large',
                                   'ami-12345', region='us-west-2',
                                   identifier='publickey',
                                   secret_identifier='privatekey',
                                   elastic_ip='208.77.188.166',
                                   placement='b', spot_instance=True,
                                   max_spot_price=0.09,
                                   price_multiplier=1.15,
                                   retry=3,
                                   retry_price_adjustment=1.1
                                   )]

In this example, a spot request will be sent with a bid price of 15% above the 24-hour average. If the request fails with the status price-too-low, the request will be resubmitted up to twice, each time with a 10% increase in the bid price. If the request succeeds, the buildslave will substantiate as normal and run any pending builds.

Libvirt

libvirt is a virtualization API for interacting with the virtualization capabilities of recent versions of Linux and other OSes. It is LGPL and comes with a stable C API, and Python bindings.

This means we know have an API which when tied to buildbot allows us to have slaves that run under Xen, QEMU, KVM, LXC, OpenVZ, User Mode Linux, VirtualBox and VMWare.

The libvirt code in Buildbot was developed against libvirt 0.7.5 on Ubuntu Lucid. It is used with KVM to test Python code on Karmic VM's, but obviously isn't limited to that. Each build is run on a new VM, images are temporary and thrown away after each build.

Setting up libvirt

We won't show you how to set up libvirt as it is quite different on each platform, but there are a few things you should keep in mind.

  • If you are running on Ubuntu, your master should run Lucid. Libvirt and apparmor are buggy on Karmic.
  • If you are using the system libvirt, your buildbot master user will need to be in the libvirtd group.
  • If you are using KVM, your buildbot master user will need to be in the KVM group.
  • You need to think carefully about your virtual network first. Will NAT be enough? What IP will my VM's need to connect to for connecting to the master?

Configuring your base image

You need to create a base image for your builds that has everything needed to build your software. You need to configure the base image with a buildbot slave that is configured to connect to the master on boot.

Because this image may need updating a lot, we strongly suggest scripting its creation.

If you want to have multiple slaves using the same base image it can be annoying to duplicate the image just to change the buildbot credentials. One option is to use libvirt's DHCP server to allocate an identity to the slave: DHCP sets a hostname, and the slave takes its identity from that.

Doing all this is really beyond the scope of the manual, but there is a vmbuilder script and a network.xml file to create such a DHCP server in contrib/ (Contrib Scripts) that should get you started:

sudo apt-get install ubuntu-vm-builder
sudo contrib/libvirt/vmbuilder

Should create an ubuntu/ folder with a suitable image in it.

virsh net-define contrib/libvirt/network.xml
virsh net-start buildbot-network

Should set up a KVM compatible libvirt network for your buildbot VM's to run on.

Configuring your Master

If you want to add a simple on demand VM to your setup, you only need the following. We set the username to minion1, the password to sekrit. The base image is called base_image and a copy of it will be made for the duration of the VM's life. That copy will be thrown away every time a build is complete.

from buildbot.buildslave.libvirt import LibVirtSlave, Connection
c['slaves'] = [LibVirtSlave('minion1', 'sekrit', Connection("qemu:///session"),
                            '/home/buildbot/images/minion1', '/home/buildbot/images/base_image')]

You can use virt-manager to define minion1 with the correct hardware. If you don't, buildbot won't be able to find a VM to start.

LibVirtSlave accepts the following arguments:

name
Both a buildbot username and the name of the virtual machine.
password
A password for the buildbot to login to the master with.
connection
Connection instance wrapping connection to libvirt.
hd_image
The path to a libvirt disk image, normally in qcow2 format when using KVM.
base_image
If given a base image, buildbot will clone it every time it starts a VM. This means you always have a clean environment to do your build in.
xml
If a VM isn't predefined in virt-manager, then you can instead provide XML like that used with virsh define. The VM will be created automatically when needed, and destroyed when not needed any longer.

OpenStack

OpenStack is a series of interconnected components that facilitates managing compute, storage, and network resources in a data center. It is available under the Apache License and has a REST interface along with a Python client.

Get an Account in an OpenStack cloud

Setting up OpenStack is outside the domain of this document. There are four account details necessary for the Buildbot master to interact with your OpenStack cloud: username, password, a tenant name, and the auth URL to use.

Create an Image

OpenStack supports a large number of image formats. OpenStack maintains a short list of prebuilt images; if the desired image is not listed, The OpenStack Compute Administration Manual is a good resource for creating new images. You need to configure the image with a buildbot slave to connect to the master on boot.

Configure the Master with an OpenStackLatentBuildSlave

With the configured image in hand, it is time to configure the buildbot master to create OpenStack instances of it. You will need the aforementioned account details. These are the same details set in either environment variables or passed as options to an OpenStack client.

OpenStackLatentBuildSlave accepts the following arguments:

name
The buildslave name.
password
A password for the buildslave to login to the master with.
flavor
The flavor ID to use for the instance.
image
A string containing the image UUID to use for the instance. A callable may instead be passed. It will be passed the list of available images and must return the image to use.

os_username

os_password

os_tenant_name

os_auth_url
The OpenStack authentication needed to create and delete instances. These are the same as the environment variables with uppercase names of the arguments.
meta
A dictionary of string key-value pairs to pass to the instance. These will be available under the metadata key from the metadata service.

Here is the simplest example of configuring an OpenStack latent buildslave.

from buildbot.buildslave.openstack import OpenStackLatentBuildSlave
c['slaves'] = [OpenStackLatentBuildSlave('bot2', 'sekrit',
                flavor=1, image='8ac9d4a4-5e03-48b0-acde-77a0345a9ab1',
                os_username='user', os_password='password',
                os_tenant_name='tenant',
                os_auth_url='http://127.0.0.1:35357/v2.0')]

The image argument also supports being given a callable. The callable will be passed the list of available images and must return the image to use. The invocation happens in a separate thread to prevent blocking the build master when interacting with OpenStack.

from buildbot.buildslave.openstack import OpenStackLatentBuildSlave

def find_image(images):
    # Sort oldest to newest.
    cmp_fn = lambda x,y: cmp(x.created, y.created)
    candidate_images = sorted(images, cmp=cmp_fn)
    # Return the oldest candiate image.
    return candidate_images[0]

c['slaves'] = [OpenStackLatentBuildSlave('bot2', 'sekrit',
                flavor=1, image=find_image,
                os_username='user', os_password='password',
                os_tenant_name='tenant',
                os_auth_url='http://127.0.0.1:35357/v2.0')]

OpenStackLatentBuildSlave supports all other configuration from the standard BuildSlave. The missing_timeout and notify_on_missing specify how long to wait for an OpenStack instance to attach before considering the attempt to have failed and email addresses to alert, respectively. missing_timeout defaults to 20 minutes.

Dangers with Latent Buildslaves

Any latent build slave that interacts with a for-fee service, such as the EC2LatentBuildSlave, brings significant risks. As already identified, the configuration will need access to account information that, if obtained by a criminal, can be used to charge services to your account. Also, bugs in the buildbot software may lead to unnecessary charges. In particular, if the master neglects to shut down an instance for some reason, a virtual machine may be running unnecessarily, charging against your account. Manual and/or automatic (e.g. nagios with a plugin using a library like boto) double-checking may be appropriate.

A comparatively trivial note is that currently if two instances try to attach to the same latent buildslave, it is likely that the system will become confused. This should not occur, unless, for instance, you configure a normal build slave to connect with the authentication of a latent buildbot. If this situation does occurs, stop all attached instances and restart the master.