turnip 0.1.1

Architecture

turnip’s architecture is designed to maximise simplicity, scalability and robustness. Each server provides roughly one service, and an installation need only run the servers that it desires. Most servers eschew local state to ease horizontal scaling, and those that do have local state can replicate and/or shard it.

There are two separate server stacks: pack and API. The pack stack communicates with Git clients via the pack protocol (git://), smart HTTP, or smart SSH. The HTTP and SSH frontends unwrap the tunneled pack protocol, and forward it onto the midends as a normal pack protocol connection. The separate HTTP API stack provides a programmatic remote interface to high-level read and write operations on the repositories

Frontends:

• Pack

• Smart HTTP

• Smart SSH

• HTTP API

Midends:

• Pack virtualisation

• API virtualisation

Backends:

• Pack

• API

Internal protocol

turnip uses an extension of the Git pack protocol for most communication between its servers. The only change is that turnip requests can specify arbitrary named parameters, not just a hostname.

The relevant part of the Git pack protocol’s git-proto-request is represented in ABNF as follows:

git-proto-request = request-command SP pathname NUL [ host-parameter NUL ]
host-parameter = "host=" hostname [ ":" port ]

turnip-proto-request alters it to this:

turnip-proto-request = request-command SP pathname NUL \*( param NUL )
param = param-name "=" param-value
param-name = \*( %x01-3C / %x3E-FF ) ; exclude NUL and =
param-value = \*%x01-FF ; exclude NUL

The only additional parameters implemented today are ‘turnip-stateless-rpc’ and ‘turnip-advertise-refs’, which are used by the smart HTTP server to proxy to the standard pack protocol.

Development

sudo lxc-create -t ubuntu -n turnip.trusty -- -r trusty -a amd64 -b $USER

sudo add-apt-repository ppa:launchpad/ppa
sudo apt-get update
cat system-dependencies.txt | sudo xargs apt-get install -y --no-install-recommends

Deployment

Turnip is deployed with the turnip juju charm, available from:

git clone https://git.launchpad.net/~canonical-launchpad-branches/charms/+source/turnip

To deploy with the local provider:

juju switch local juju bootstrap juju deploy –repository=/path/to/loca/charm/repo/root local:trusty/turnip

0.1.1 (2015-06-11)

• Add a merge detection API.

0.1 (2015-06-02)

• Initial release.