Building a Deploy

The definitive guide to building a pyinfra deploy:

Layout

  • *.py - files that describe deploys
  • inventories/*.py - files that describe different inventories
  • group_data/*.py - files that describe data for groups
  • templates/*.jn2 - templates used in the deploys
  • files/* - files used in the deploys
  • roles/*.py - files that describe role specific deploys
  • config.py - optional config and hooks

Inventory

Inventory files contain groups of hosts. Groups are defined as a list or tuple of hosts. For example, this inventory creates two groups, “app_servers” and “db_servers”:

# inventories/production.py

app_servers = [
    'app-1.net',
    'app-2.net'
]

db_servers = [
    'db-1.net',
    'db-2.net',
    'db-3.net'
]

In addition to the groups defined in the inventory, all the hosts are added to two more groups: “all” and the name of the inventory file, in this case “production”. Both can be overriden by defining them in the inventory.

Data

Data allows you to separate deploy variables from the deploy script. With data per host and per group, you can easily build deploys that satisfy multiple environments.

Host Data

Arbitrary data can be assigned in the inventory and used at deploy-time. You just pass a tuple (hostname, data) instead of just the hostname:

# inventories/production.py

app_servers = [
    'app-1.net',
    ('app-2.net', {'some_key': True})
]

Group Data

Group data files can be used to attach data to groups of host. They are placed in group_data/<group_name>.py. This means group_data/all.py can be used to attach data to all hosts (unless you override the “all” group).

Data files are just Python, all lowercase attributes not starting in _ will be included, eg:

# group_data/production.py

app_user = 'myuser'
app_dir = '/opt/myapp'

Authenticating with Data

One of the most important use-cases for data is authenticating with the remote host. Instead of passing --key, --user, etc to the CLI, or running a SSH agent, you can define these details within host and group data. The attributes available:

ssh_port = 22
ssh_user = 'ubuntu'
ssh_key = '~/.ssh/some_key'
ssh_key_password = 'password for key'
# ssh_password = 'password auth is bad'

Data Hierarchy

The same keys can be defined for host and group data - this means we can set a default in all.py and override it on a group or host basis. When accessing data, the first match in the following is returned:

  • “Override” data passed in via CLI args
  • Host data as defined in the inventory file
  • Normal group data
  • “all” group data
Debugging data issues:
pyinfra contains a --debug-data option which can be used to explore the data output per-host for a given inventory/deploy.

Data Example

Lets say you have an app that you wish to deploy in two environments: staging and production, with the dev VM as the default. A good layout for this would be:

  • deploy.py
  • inventories/production.py - production inventory
  • inventories/staging.py - staging inventory
  • group_data/all.py - shared data
  • group_data/production.py - production data
  • group_data/staging.py - staging data

The “all” group data contains any shared info and defaults:

# group_data/all.py

env = 'dev'
git_repo = 'https://github.com/Fizzadar/pyinfra'

And the production/staging data describe the differences:

# group_data/production.py

env = 'production'
git_branch = 'master'
# group_data/staging.py

env = 'staging'
git_branch = 'develop'

Operations

Now that you’ve got an inventory of hosts and know how to auth with them, you can start writing the deploy. This is described in a Python file normally situated in the top level of the deploy directory.

In this file, eg deploy.py, you import pyinfra modules. Each of these contains a number of operations. You call these operations inside the deploy file, with arguments describing remote state, and pyinfra uses this to run the deploy.

For example, this deploy will ensure that user “pyinfra” exists with home directory “/home/pyinfra”, and that the “/var/log/pyinfra.log” file exists and is owned by that user.

# deploy.py

# Import pyinfra modules, each containing operations to use
from pyinfra.modules import server, files

# Ensure the state of a user
server.user(
    'pyinfra',
    home='/home/pyinfra'
)

# Ensure the state of files
files.file(
    '/var/log/pyinfra.log',
    user='pyinfra',
    group='pyinfra',
    permissions='644',
    sudo=True
)

Uses the server module and files module. You can see all the modules in the modules index.

Naming operations:
Pass a set object as the first argument to name the operation, which will appear during a deploy. By default the operation module, name and arguments are shown:
server.user(
    {'Ensure user pyinfra'},  # the contents of the set will become the op name
    'pyinfra',
    home='/home/pyinfra'
)

Using Data

Adding data to inventories was described above - you can access it within a deploy on host.data:

from pyinfra import host
from pyinfra.modules import server

# Ensure the state of a user based on host/group data
server.user(
    host.data.app_user,
    home=host.data.app_dir
)
String formatting:
pyinfra supports jinja2 style string arguments, which should be used over Python’s builtin string formatting where you expect the final string to change per host. This is because pyinfra groups operations by their arguments:
from pyinfra import host
from pyinfra.modules import server

server.user(
    host.data.app_user,
    '/opt/{{ host.data.app_dir }}'  # for multiple values of host.data.app_dir we still
                                    # generate a single operation
)

Operation Meta

Operation meta can be used during a deploy to change the desired operations:

from pyinfra.modules import server

# Run an operation, collecting its meta output
meta = server.user(
    'myuser'
)

# If we added a user above, do something extra
if meta.commands:
    server.shell('# add server to sudo, etc...')

Facts

Facts allow you to use information about the target host to change the operations you use. A good example is switching between apt & yum depending on the Linux distribution. Like data, facts are accessed on host.fact:

from pyinfra import host
from pyinfra.modules import apt, yum

if host.fact.linux_distribution == 'CentOS':
    yum.packages(
        'nano',
        sudo=True
    )
else:
    apt.packages(
        'nano',
        sudo=True
    )

Some facts also take a single argument, for example the directory or file facts. The facts index lists the available facts and their arguments.

Includes/Roles

Roles can be used to break out deploy logic into multiple files. They can also be used to limit the contained operations to a subset of hosts. Roles can be included using local.include.

from pyinfra import local, inventory

# Operations in this file will be added to all hosts
local.include('roles/my_role.py')

# Operations in this file will be added to the hosts in group "my_group"
local.include('roles/limited_role.py', hosts=inventory.my_group)

See more in patterns: groups & roles.

Config

There are a number of configuration options for how deploys are managed. These can be defined at the top of a deploy file, or in a config.py alongside the deploy file. See the full list of options & defaults.

# config.py or top of deploy.py

# SSH connect timeout
TIMEOUT = 1

# Fail the entire deploy after 10% of hosts fail
FAIL_PERCENT = 10
config.py advantage:
When added to config.py, these options will take affect when using pyinfra --fact or --run.

Hooks

Deploy hooks are executed by the CLI at various points during the deploy process. Like config, they can be defined in a config.py or at the top of the deploy file:

  • before_connect
  • before_facts
  • before_deploy
  • after_deploy

These can be used, for example, to check the right branch before connecting or to build some clientside assets locally before fact gathering. Hooks all take data, state as arguments:

# config.py or top of deploy.py

from pyinfra import hook

@hook.before_connect
def my_callback(data, state):
    print('Before connect hook!')

To abort a deploy, a hook can raise a hook.Error which the CLI will handle.

When executing commands locally inside a hook (ie webpack build), you should always use the pyinfra.local module:

@hook.before_connect
def my_callback(data, state):
    # Check something local is correct, etc
    branch = local.shell('git rev-parse --abbrev-ref HEAD')
    app_branch = data.app_branch

    if branch != app_branch:
        # Raise hook.Error for pyinfra to handle
        raise hook.Error('We\'re on the wrong branch (want {0}, got {1})!'.format(
            branch, app_branch
        ))