// file      : doc/manual.cli
// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

"\name=build2-build-bot-manual"
"\subject=build bot"
"\title=Build Bot"

// NOTES
//
// - Maximum <pre> line is 70 characters.
//

"
\h0#preface|Preface|

This document describes \c{bbot}, the \c{build2} build bot.

\h1#intro|Introduction|

\h1#arch|Architecture|

The \c{bbot} architecture includes several layers for security and
manageability. At the top we have a \c{bbot} running in the \i{controller}
mode. The controller monitors various \i{build sources} for \i{build
tasks}. For example, a controller may poll a \c{brep} instances for any new
packages to built as well as monitor a \c{git} repository for any new commits
to test. There can be several layers of controllers with \c{brep} being just a
special kind. A machine running a \c{bbot} instance in the controller mode is
called a \i{controller host}.

Below the controllers we have a \c{bbot} running in the \i{agent} mode
normally on Build OS. The agent polls its controllers for \i{build tasks} to
perform. A machine running a \c{bbot} instance in the agent mode is called a
\i{build host}.

The actual building is performed in the virtual machines and/or containers
that are executed on the build host. Inside virtual machines/containers,
\c{bbot} is running in the \i{worker mode} and receives build tasks from its
agent. Virtual machines and containers running a \c{bbot} instance in the
worker mode are collectively called \i{build machines}.

Let's now examine the workflow in the other direction, that is, from a worker
to a controller. Once a build machine is booted (by the agent), the worker
inside connects to the TFTP server running on the build host and downloads the
\i{build task manifest}. It then proceeds to perform the build task and
uploads the \i{build result manifest} (which includes build logs) to the TFTP
server.

Once an agent receives a build task for a specific build machine, it goes
through the following steps. First, it creates a directory on its TFTP server
with the \i{build machine id} as its name and places the build task manifest
inside. Next, it makes a throw-away snapshot of the build machine and boots
it. After booting the build machine, the agent monitors the machine directory
on its TFTP server for the build result manifest (uploaded by the worker once
the build has completed). Once the result manifest is obtained, the agent
shuts down the build machine and discards its snapshot.

To obtains a build task the agent polls via HTTP/HTTPS one or more
controllers. Before each poll request the agent enumerates the available build
machines and sends this information as part of the request. The controller
responds with a build task manifest that identifies a specific build machine
to use.

If the controller has higher-level controllers (for example, \c{brep}), then
it aggregates the available build machines from its agents and polls these
controllers (just as an agent would), forwarding build tasks to suitable
agents. The controller may also be configured to monitor build sources, such
as SCM repositories, directly in which case it generates build tasks itself.

In this architecture the build results are propagated up the chain: from a
worker, to its agent, to its controller, and so on. A controller that is the
final destination of a build result uses email to notify interested parties of
the outcome. For example, \c{brep} would send a notification to the package
owner if the build failed. Similarly, a \c{bbot} controller that monitors a
\c{git} repository would send an email to a committer if their commit caused a
build failure. The email would include a link (normally HTTP/HTTPS) to the
build logs hosted by the controller.
"