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Ansible Deploy Interface

Ansible is a mature and popular automation tool, written in Python and requiring no agents running on the node being configured. All communications with the node are by default performed over secure SSH transport.

The ansible deploy interface uses Ansible playbooks to define the deployment logic. It is not based on Ironic Python Agent (IPA) and does not generally need IPA to be running in the deploy ramdisk.

Overview

The main advantage of this deploy interface is extended flexibility in regards to changing and adapting node deployment logic for specific use cases, via Ansible tooling that is already familiar to operators.

It can be used to shorten the usual feature development cycle of

  • implementing logic in ironic,
  • implementing logic in IPA,
  • rebuilding deploy ramdisk,
  • uploading deploy ramdisk to Glance/HTTP storage,
  • reassigning deploy ramdisk to nodes,
  • restarting ironic-conductor service(s) and
  • running a test deployment

by using a “stable” deploy ramdisk and not requiring ironic-conductor restarts (see Extending playbooks).

The main disadvantage of this deploy interface is the synchronous manner of performing deployment/cleaning tasks. A separate ansible-playbook process is spawned for each node being provisioned or cleaned, which consumes one thread from the thread pool available to the ironic-conductor process and blocks this thread until the node provisioning or cleaning step is finished or fails. This has to be taken into account when planning an ironic deployment that enables this deploy interface.

Each action (deploy, clean) is described by a single playbook with roles, which is run whole during deployment, or tag-wise during cleaning. Control of cleaning steps is through tags and auxiliary clean steps file. The playbooks for actions can be set per-node, as can the clean steps file.

Features

Similar to deploy interfaces relying on Ironic Python Agent (IPA), this deploy interface also depends on the deploy ramdisk calling back to ironic API’s heartbeat endpoint.

However, the driver is currently synchronous, so only the first heartbeat is processed and is used as a signal to start ansible-playbook process.

User images

Supports whole-disk images and partition images:

  • compressed images are downloaded to RAM and converted to disk device;
  • raw images are streamed to disk directly.

For partition images the driver will create root partition, and, if requested, ephemeral and swap partitions as set in node’s instance_info by the Compute service or operator. The create partition table will be of msdos type by default, the node’s disk_label capability is honored if set in node’s instance_info (see also Choosing the disk label).

Configdrive partition

Creating a configdrive partition is supported for both whole disk and partition images, on both msdos and GPT labeled disks.

Root device hints

Root device hints are currently supported in their basic form only, with exact matches (see Specifying the disk for deployment (root device hints) for more details). If no root device hint is provided for the node, the first device returned as part of ansible_devices fact is used as root device to create partitions on or write the whole disk image to.

Node cleaning

Cleaning is supported, both automated and manual. The driver has two default clean steps:

  • wiping device metadata
  • disk shredding

Their priority can be overridden via [deploy]\erase_devices_metadata_priority and [deploy]\erase_devices_priority options, respectively, in the ironic configuration file.

As in the case of this driver all cleaning steps are known to the ironic-conductor service, booting the deploy ramdisk is completely skipped when there are no cleaning steps to perform.

Note

Aborting cleaning steps is not supported.

Logging

Logging is implemented as custom Ansible callback module, that makes use of oslo.log and oslo.config libraries and can re-use logging configuration defined in the main ironic configuration file to set logging for Ansible events, or use a separate file for this purpose.

It works best when journald support for logging is enabled.

Requirements

Ansible

Tested with, and targets, Ansible 2.5.x

Bootstrap image requirements

  • password-less sudo permissions for the user used by Ansible
  • python 2.7.x
  • openssh-server
  • GNU coreutils
  • utils-linux
  • parted
  • gdisk
  • qemu-utils
  • python-requests (for ironic callback and streaming image download)
  • python-netifaces (for ironic callback)

A set of scripts to build a suitable deploy ramdisk based on TinyCore Linux and tinyipa ramdisk, and an element for diskimage-builder can be found in ironic-staging-drivers project but will be eventually migrated to the new ironic-python-agent-builder project.

Setting up your environment

  1. Install ironic (either as part of OpenStack or standalone)
    • If using ironic as part of OpenStack, ensure that the Image service is configured to use the Object Storage service as backend, and the Bare Metal service is configured accordingly, see Configure the Image service for temporary URLs.
  2. Install Ansible version as specified in ironic/driver-requirements.txt file
  3. Edit ironic configuration file
    1. Add ansible to the list of deploy interfaces defined in [DEFAULT]\enabled_deploy_interfaces option.
    2. Ensure that a hardware type supporting ansible deploy interface is enabled in [DEFAULT]\enabled_hardware_types option.
    3. Modify options in the [ansible] section of ironic’s configuration file if needed (see Configuration file).
  4. (Re)start ironic-conductor service
  5. Build suitable deploy kernel and ramdisk images
  6. Upload them to Glance or put in your HTTP storage
  7. Create new or update existing nodes to use the enabled driver of your choice and populate Driver properties for the Node when different from defaults.
  8. Deploy the node as usual.

Ansible-deploy options

Configuration file

Driver options are configured in [ansible] section of ironic configuration file, for their descriptions and default values please see configuration file sample.

Driver properties for the Node

Set them per-node via baremetal node set command, for example:

baremetal node set <node> \
    --deploy-interface ansible \
    --driver-info ansible_username=stack \
    --driver-info ansible_key_file=/etc/ironic/id_rsa

ansible_username

User name to use for Ansible to access the node. Default is taken from [ansible]/default_username option of the ironic configuration file (defaults to ansible).

ansible_key_file

Private SSH key used to access the node. Default is taken from [ansible]/default_key_file option of the ironic configuration file. If neither is set, the default private SSH keys of the user running the ironic-conductor process will be used.

ansible_deploy_playbook

Playbook to use when deploying this node. Default is taken from [ansible]/default_deploy_playbook option of the ironic configuration file (defaults to deploy.yaml).

ansible_shutdown_playbook

Playbook to use to gracefully shutdown the node in-band. Default is taken from [ansible]/default_shutdown_playbook option of the ironic configuration file (defaults to shutdown.yaml).

ansible_clean_playbook

Playbook to use when cleaning the node. Default is taken from [ansible]/default_clean_playbook option of the ironic configuration file (defaults to clean.yaml).

ansible_clean_steps_config

Auxiliary YAML file that holds description of cleaning steps used by this node, and defines playbook tags in ansible_clean_playbook file corresponding to each cleaning step. Default is taken from [ansible]/default_clean_steps_config option of the ironic configuration file (defaults to clean_steps.yaml).

ansible_python_interpreter

Absolute path to the python interpreter on the managed machine. Default is taken from [ansible]/default_python_interpreter option of the ironic configuration file. Ansible uses /usr/bin/python by default.

Customizing the deployment logic

Expected playbooks directory layout

The [ansible]\playbooks_path option in the ironic configuration file is expected to have a standard layout for an Ansible project with some additions:

<playbooks_path>
|
\_ inventory
\_ add-ironic-nodes.yaml
\_ roles
 \_ role1
 \_ role2
 \_ ...
|
\_callback_plugins
 \_ ...
|
\_ library
 \_ ...

The extra files relied by this driver are:

inventory

Ansible inventory file containing a single entry of conductor ansible_connection=local. This basically defines an alias to localhost. Its purpose is to make logging for tasks performed by Ansible locally and referencing the localhost in playbooks more intuitive. This also suppresses warnings produced by Ansible about hosts file being empty.

add-ironic-nodes.yaml

This file contains an Ansible play that populates in-memory Ansible inventory with access information received from the ansible-deploy interface, as well as some per-node variables. Include it in all your custom playbooks as the first play.

The default deploy.yaml playbook is using several smaller roles that correspond to particular stages of deployment process:

  • discover – e.g. set root device and image target
  • prepare – if needed, prepare system, for example create partitions
  • deploy – download/convert/write user image and configdrive
  • configure – post-deployment steps, e.g. installing the bootloader

Some more included roles are:

  • shutdown – used to gracefully power the node off in-band
  • clean – defines cleaning procedure, with each clean step defined as separate playbook tag.

Extending playbooks

Most probably you’d start experimenting like this:

  1. Create a copy of deploy.yaml playbook in the same folder, name it distinctively.
  2. Create Ansible roles with your customized logic in roles folder.
    1. In your custom deploy playbook, replace the prepare role with your own one that defines steps to be run before image download/writing. This is a good place to set facts overriding those provided/omitted by the driver, like ironic_partitions or ironic_root_device, and create custom partitions or (software) RAIDs.
    2. In your custom deploy playbook, replace the configure role with your own one that defines steps to be run after image is written to disk. This is a good place for example to configure the bootloader and add kernel options to avoid additional reboots.
    3. Use those new roles in your new playbook.
  3. Assign the custom deploy playbook you’ve created to the node’s driver_info/ansible_deploy_playbook field.
  4. Run deployment.
    1. No ironic-conductor restart is necessary.
    2. A new deploy ramdisk must be built and assigned to nodes only when you want to use a command/script/package not present in the current deploy ramdisk and you can not or do not want to install those at runtime.

Variables you have access to

This driver will pass the single JSON-ified extra var argument to Ansible (as in ansible-playbook -e ..). Those values are then accessible in your plays as well (some of them are optional and might not be defined):

ironic:
  nodes:
  - ip: "<IPADDRESS>"
    name: "<NODE_UUID>"
    user: "<USER ANSIBLE WILL USE>"
    extra: "<COPY OF NODE's EXTRA FIELD>"
  image:
    url: "<URL TO FETCH THE USER IMAGE FROM>"
    disk_format: "<qcow2|raw|...>"
    container_format: "<bare|...>"
    checksum: "<hash-algo:hashstring>"
    mem_req: "<REQUIRED FREE MEMORY TO DOWNLOAD IMAGE TO RAM>"
    tags: "<LIST OF IMAGE TAGS AS DEFINED IN GLANCE>"
    properties: "<DICT OF IMAGE PROPERTIES AS DEFINED IN GLANCE>"
  configdrive:
    type: "<url|file>"
    location: "<URL OR PATH ON CONDUCTOR>"
  partition_info:
    label: "<msdos|gpt>"
    preserve_ephemeral: "<bool>"
    ephemeral_format: "<FILESYSTEM TO CREATE ON EPHEMERAL PARTITION>"
    partitions: "<LIST OF PARTITIONS IN FORMAT EXPECTED BY PARTED MODULE>"
  raid_config: "<COPY OF NODE's TARGET_RAID_CONFIG FIELD>"

ironic.nodes

List of dictionaries (currently of only one element) that will be used by add-ironic-nodes.yaml play to populate in-memory inventory. It also contains a copy of node’s extra field so you can access it in the playbooks. The Ansible’s host is set to node’s UUID.

ironic.image

All fields of node’s instance_info that start with image_ are passed inside this variable. Some extra notes and fields:

  • mem_req is calculated from image size (if available) and config option [ansible]extra_memory.
  • if checksum is not in the form <hash-algo>:<hash-sum>, hashing algorithm is assumed to be md5 (default in Glance).
  • validate_certs – boolean (yes/no) flag that turns validating image store SSL certificate on or off (default is ‘yes’). Governed by [ansible]image_store_insecure option in ironic configuration file.
  • cafile – custom CA bundle to use for validating image store SSL certificate. Takes value of [ansible]image_store_cafile if that is defined. Currently is not used by default playbooks, as Ansible has no way to specify the custom CA bundle to use for single HTTPS actions, however you can use this value in your custom playbooks to for example upload and register this CA in the ramdisk at deploy time.
  • client_cert – cert file for client-side SSL authentication. Takes value of [ansible]image_store_certfile option if defined. Currently is not used by default playbooks, however you can use this value in your custom playbooks.
  • client_key – private key file for client-side SSL authentication. Takes value of [ansible]image_store_keyfile option if defined. Currently is not used by default playbooks, however you can use this value in your custom playbooks.

ironic.partition_info.partitions

Optional. List of dictionaries defining partitions to create on the node in the form:

partitions:
- name: "<NAME OF PARTITION>"
  unit: "<UNITS FOR SIZE>"
  size: "<SIZE OF THE PARTITION>"
  type: "<primary|extended|logical>"
  align: "<ONE OF PARTED_SUPPORTED OPTIONS>"
  format: "<PARTITION TYPE TO SET>"
  flags:
    flag_name: "<bool>"

The driver will populate this list from root_gb, swap_mb and ephemeral_gb fields of instance_info. The driver will also prepend the bios_grub-labeled partition when deploying on GPT-labeled disk, and pre-create a 64 MiB partition for configdrive if it is set in instance_info.

Please read the documentation included in the ironic_parted module’s source for more info on the module and its arguments.

ironic.partition_info.ephemeral_format

Optional. Taken from instance_info, it defines file system to be created on the ephemeral partition. Defaults to the value of [pxe]\default_ephemeral_format option in ironic configuration file.

ironic.partition_info.preserve_ephemeral

Optional. Taken from the instance_info, it specifies if the ephemeral partition must be preserved or rebuilt. Defaults to no.ironic.raid_config

Taken from the target_raid_config if not empty, it specifies the RAID configuration to apply.

As usual for Ansible playbooks, you also have access to standard Ansible facts discovered by setup module.

Included custom Ansible modules

The provided playbooks_path/library folder includes several custom Ansible modules used by default implementation of deploy and prepare roles. You can use these modules in your playbooks as well.

stream_url

Streaming download from HTTP(S) source to the disk device directly, tries to be compatible with Ansible’s get_url module in terms of module arguments. Due to the low level of such operation it is not idempotent.

ironic_parted

creates partition tables and partitions with parted utility. Due to the low level of such operation it is not idempotent. Please read the documentation included in the module’s source for more information about this module and its arguments. The name is chosen so that the parted module included in Ansible is not shadowed.

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