When any system boots, Zygote's job is to tell it what to do.
Zygote leverages ERB templates empower complex decision making where systems are otherwise limited to simple protocols.
Using iPXE, Zygote can direct servers to bootstrap, run recovery scripts, perform system burnin, or other task that might normally be manual.
For switches, Zygote may be used to render switch configurations, and relay them back via Zero Touch Provisioning.
Zygote can control any DHCP-capable device.
Cells are zygote's concept of modules and name-spacing. Cells with ERB templates are exposed as endpoints, and provide the interface to zygote.
A cell can call back to other cells during its operation, enabling zygote to proxy requests so that the client machine doesn't to authenticate.
Cells can also be used to logically group common functionality, so that cells can share logic server-side by leveraging ERB partials.
Each cell can also specify static configuration values in cells.yml. These values will be available in the render-time context of the cell.
require 'zygote'
Zygote::Server.new(
cells: File.expand_path('../cells', __FILE__)
).run
Where 'cells' is a path to cells containing erb templates describing how to boot your system - shown in greater detail below.
Additionally, create a configuration file at 'config/cells.yml' of the following structure:
index:
timeout: 0 # timeout in seconds, 0 for none
cells:
installers:
delegate: live
menu: # A menu with submenu entries
class: os
label: "Install an operating system"
submenu:
ubuntu:
label: "Install Ubuntu"
args:
arbitrary: data
memtest:
menu:
class: util
label: "Run Memtest86"
args:
kernel_params: console=ttyS1,115200n8
passes: 5
Zygote supports bootstrapping servers through generating iPXE scripted menus
It's probably necessary to gain a basic understanding of the iPXE scripting commands to generate meaningful scripts.
Zygote reads cells.yml, and generates menus and submenus. Every menu entry has a top-level iPXE symbol, and every submenu has a symbol formed by joining the top-level menu grouping with the specific menu entry.
For instance, a top-level menu item called 'memtest' would tagged in iPXE with:
:memtest
This symbol would be called (via an iPXE goto) if the memtest menu item is selected.
Likewise, a submenu called 'utility' with the entry 'rescue' would be tagged as:
:utility-rescue
Each menu and submenu can have a user-friendly description using the 'label' field. Additional arguments or parameters are allowed nested under the 'args' field. Any URI parameters are merged with this, as is any JSON encoded post data.
Each entry may invoke an action, by default the action is called 'boot', but this can be overriden with the 'action' field.
Each entry will by default correspond to rendering an erb file at:
cell/<entry>/<action>
Where this corresponds to a file on disk called:
cells/<entry>/<action>.erb
So, if you have an entry called 'memtest', and you want to use the default action of 'boot', create the file with the necessary iPXE directives to boot it at:
cells/memtest/boot.erb
If you want to use the boot logic of another cell, you can delegate to it using the 'delegate' field. So we could have memtest delegate to using another cell's named 'default' to boot it if we chose to. This can be useful if your boot logic is shared between cells.
If you want to share code within any erb file, you may use a partial. All partials are relative to the cells directory, and strings or symbols are accepted.
For instance, adding:
<%= partial('util/common', {some: 'optional', variables: 'to help render'}) %>
The template at cells/util/common.erb will be rendered in the current template.
Zygote supports automation through a simple queuing mechanism.
Let's say we have the asset SKU-1234567, as identified by iPXE, and we want to run the cell 'ubuntu-automatic'
curl -X POST localhost:7000/queue/SKU-1234567/ubuntu-automatic
The next time the asset boots, the boot menu will be bypassed entirely and the ubuntu-automatic entry will be loaded.
Any post parameters provided will be merged into the options hash at boot time, which allows for fairly dynamic behaviour.
You may of course push multiple cells to the queue for a given asset. This allows you to chain from one cell into another - assuming they each complete and reboot successfully.
By adding the selected_cell parameter, you may jump directly to a particular cell to execute using an iPXE goto statement. This is quite powerful, as it prevents the need for human interaction. Combined with zygote's queueing, you can chain from one action into another by rebooting after each action.
So, if we set the URI parameter selected_cell=memtest, the menu will never be displayed, and we'll jump directly to the memtest label, and execute the memtest action.
Before the iPXE menu is rendered, an identifier may mutate the parameters used at boot time arbitrarily. This provides a means to hook in custom code to alter the boot behavior. By subclassing Zygote::Identifier you may shadow the identify method, to mutate the params hash as shown:
module Zygote
class MyIdentifier < Zygote::Identifier
def identify
@params['selected_cell'] = MyCustomRubyCode.decide_what_to_do
@params
end
end
end
Define this code after requiring the zygote gem.
You may of course perform basic queue operations:
You may view the JSON of the queue:
curl -X GET localhost:7000/queue/SKU-1234567
You may purge the queue completely:
curl -X DELETE localhost:7000/queue?sku=1234567 # FIXME: this is orthogonal, figure out why DELETE collides with GET
Setting DEBUG=true (or to anything) will cause zygote to print the fully body of all requests and responses.
Tested automatically using travis ci.
Most tests are fixture based, as the app primarily renders templates.
To regenerate fixtures, set FIXTURE_RECORD=true before running test.