GOV.UK Fabric Scripts

Fabric is a command-line tool for application deployment and systems administration tasks. It allows the user to run commands across a server farm.

Local usage and environment setup

The tool is intended to be configured and run on your local workstation/laptop. You should use virtualenv to create an isolated Python environment.

To install pip, virtualenv and set up the environment:

$ sudo easy_install pip
$ sudo pip install virtualenv
$ mkdir ~/venv
$ virtualenv ~/venv/fabric-scripts

To enable the virtual environment for this session (you will need to do this for each new terminal window):

$ . ~/venv/fabric-scripts/bin/activate

Setup

To install the dependencies:

$ pip install -Ur requirements.txt

NB: if you get a "pip: command not found" error, run this first:

$ sudo easy_install pip

Configure it (see the fabric documentation for more examples),

$ echo 'user = jimbob' >> ~/.fabricrc

Commands

You can view a list of the available tasks:

$ fab -l

And execute against an environment and set of hosts like so:

$ fab integration all hosts
...
$ fab integration class:frontend do:'uname -a'
$ fab integration class:cache,bouncer do:uptime
...

Targetting groups of machines

Fabric tasks can be run on groups of machines in a variety of different ways.

By puppet class:

# target all machines that have the 'govuk::safe_to_reboot::yes' class
$ fab integration puppet_class:govuk::safe_to_reboot::yes do:'uname -a'

By numeric machine suffix:

# target all machines that end in '2'
$ fab integration numbered:2 do:'uname -a'

By node type (as defined in puppet):

# target all 'frontend' machines
$ fab integration node_type:frontend do:'uname -a'

By the node name:

# target just one node
$ fab production -H backend-3.backend do:'uname -a'

Remote usage (legacy)

It was previously possible to use these scripts from the jumpboxes via the govuk_fab wrapper. This is no longer supported as it relied on SSH agent forwarding, which is a Bad Thing because other people with root access to that jumpbox would be able to re-use any of the private keys in your agent.

You should convert to the [local usage](#Local usage) method described above and ensure that you do not have the following option anywhere in your ~/.ssh/config:

ForwardAgent yes

Syncing postgres machines

An example:

fab <env> -H '<src_db>' postgresql.sync:<db_name>,<dst_db> -A

the -A must be specified to forward the agent

This will sync the specified database <db_name> from the machine with the hostname of <src_db> to the machine with hostaname <dst_db>. It will destroy data on the destination db.