Introduction

Conveyor is a simple continuous deployment framework built on top of Apache Zookeeper. Conveyor itself consists of two components:

• conveyor: Daemon program used to watch for and deploy new applications
• hoist: Command line client used to manage data within ZooKeeper

Typically, the conveyor daemon runs on each application server, and the hoist command is invoked from your continuous integration server (e.g. Hudson CI, etc.) every time a new application is ready to be deployed:

$ hoist application create myapp 1.0

This command will create/update an application node within ZooKeeper. The conveyor daemons will see this change almost immediately and run the appropriate commands to install or update the application.

Now of course, you probably don't want all of your application servers to deploy the application at the same time, because that will almost certainly lead to a brief period of downtime while the deployment is occurring. This is where Conveyor's concept of "slots" comes in. By default the hoist command creates new applications with just one slot. When an application change is detected, the first conveyor daemon that sees this change will "occupy" that free slot until the application is deployed. In the meantime,the rest of the conveyor daemons will have to wait until another free slot becomes available. The result is a staggered deployment across your entire farm.

So how does Conveyor know how to deploy your application? This is where the get-version-cmd and deploy-cmd attributes of an application come in. Before a conveyor daemon deploys an application, it compares the output of the command specified by get-version-cmd to the version associated with the application in ZooKeeper. If the versions differ, then the comand specified by deploy-cmd is run. A simple example for an application distributed as a .deb packages might look something like this:

get-version-cmd: /usr/bin/dpkg-query --showformat '${Version}' --show %(id)s
deploy-cmd: /usr/bin/aptitude install %(id)s=%(version)s

Notice the placeholders that look like %(foo)s in the commands above. This is how you reference information about a particular application in ZooKeeper.

Installation

1. Set up a Zookeeper server/ensamble (in some cases, this may be as simple as: aptitude install zookeeper)
2. Install the Python bindings for ZooKeeper everywhere that conveyor and hoist will be run (again, this may be as simple as: aptitude install python-zookeeper)
3. Install Conveyor (FIXME)

Configuration

FIXME

To Do

• Implement proper ACLs
• Finish installation/configuration documentation
• Upload package to PyPI

Known Issues

• Segfault when reconnecting to ZooKeeper (https://issues.apache.org/jira/browse/ZOOKEEPER-740)

Authors

• Michael T. Conigliaro <mike [at] conigliaro [dot] org>