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

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

To installpip,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

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 (seethe fabric documentation for more examples),

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

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...

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'

It was previously possible to use these scripts from the jumpboxes via thegovuk_fab wrapper. This is no longer supported as it relied on SSH agentforwarding, which is a Bad Thing because other people with root access tothat 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 aboveand ensure that you do not have the following option anywhere in your~/.ssh/config:

ForwardAgent yes

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 thehostname of<src_db> to the machine with hostaname<dst_db>. It will destroy data on the destination db.