Advanced Usage

Writing a custom component (TODO)

Using 3rd party libraries within batou

Sometimes, when writing custom components, you may need additional Python packages, for example to configure databases by connecting directly to their SQL interface instead of using their command line clients.

You can use additional Python packages by adding a requirements.txt file to your batou project repository:

$ tree
.
├── batou
├── components
│   └── myapp
│       └── component.py
├── environments
│   └── local.cfg
└── requirements.txt
requirements.txt
sqlalchemy

The next time when you call batou the dependencies will be automatically updated. When deploying then the requirements will also be installed on the remote hosts.

$ ./batou
Installing sqlalchemy
usage: batou [-h] [-d] {deploy,secrets,init,update} ...

Note

batou already provides a number of packages that it depends on. If you create contradicting requirements then this may lead to batou failing. You will see pip complaining in that case.

Multiple components in a single component.py (TODO)

Skipping individual hosts or components when deploying (TODO)

Events (TODO)

Using bundle transfers if the repository server is not reachable from your remote server (TODO)

Timeout (TODO)

VFS mapping for development (TODO)

VFS mapping with explicit rewrite rules (TODO)

Extended service discovery options (TODO)

Platform-specific components

New in version 1.4.

Platform-specific components allow to customize behavior depending on the system or “platform” the target system runs as. Examples:

  • Production system on Gentoo, local development on Ubuntu, or
  • All VMs on Ubuntu but Oracle is being run with RedHat.

To define a platform specific aspects, you use the platform class decorator. Example:

import batou.component
import batou.lib.file


class Test(batou.component.Component):

    def configure(self):
        self += batou.lib.file.File('base-component')


@batou.component.platform('nixos', Test)
class TestNixos(batou.component.Component):

    def configure(self):
        self += batou.lib.file.File('i-am-nixos')


@batou.component.platform('ubuntu', Test)
class TestUbuntu(batou.component.Component):

    def configure(self):
        self += batou.lib.file.File('i-am-ubuntu')

The platform is then defined in the environment:

[environment]
platform = default-platform

[host:nixos]
# Host specifc override:
platform = nixos
components = test

[host:ubuntu]
# Host specifc override:
platform = ubuntu
components = test

Host-specific data

New in version 1.5.

Host-specifc data allows to set environment depentend data for a certain host. It looks like this in an environment configuration:

[host:myhost00]
components = test
data-alias = nice-alias.for.my.host.example.com

In a component you can access all data attributes via the host’s data dictionary:

def configure(self):
    alias = self.host.data['alias']

The data- prefix was chosen in resemblance of the HTML standard.

DNS overrides

New in version 1.6

When migrating services automatic DNS lookup of IP addresses to listen on can be cumbersome. You want to deploy the service before the DNS changes become active. This is where DNS overrides can help.

The DNS overrides short circuit the resolving completely for the given host names.

Example:

[environment]
...

[resolver]
www.example.com =
    3.2.1.4
    ::2

Whenever batou configuration (i.e. batou.utils.Address) looks up www.example.com it will result in the addresses 3.2.1.4 and ::2.

The overrides support IPv4 and IPv6. You should only set one IP address per type for each host name.

Note

You cannot override the addresses of the configured hosts. The SSH connection will always use genuine name resolving.

context manager (TODO)

last_updated (TODO)

prepare, |=, component._ (TODO)

workdir overriding (TODO)

batou.c (TODO)

ordered alphabetically (significant for imports)