Documentation for Temporary Container Experiment Playbook

Overview

• Playbook Name: Temporary Container Experiment
• Version: 0.8.1
• Description: This playbook establishes an ephemeral storage environment using device mapper and btrfs subvolumes to manage systemd-nspawn containers. The playbook also ensures idempotency and deterministic naming conventions for loop devices, and generates the loop_device.target file to store the btrfs subvolumes used to hold the volume pool btrfs subvolumes, which refer the pool of storage to be used inside another system. Storage Pool refers the host or builder, the Volume Pool refers to the target system or guest container

Usage

This playbook can be executed with these overridable values when running ansible-playbook playbooks/Sandbox/Temporary_Container_Experiment.yml ...

-e [container_name=<CONTAINER_NAME>][,container_collection=<COLLECTION_NAME>][,ephemeral_base_path=<EPHEMERAL_BASE_PATH>]'

Scope

The playbook broadens the category to instantiate device mapper-based storage setups, ensuring idempotent naming for loop devices.

Requirements

1. Setup Storage Pool Target: Configure with the Storage role.
2. Setup Volume Pool: This includes targeting a block device image through a loop device, which is specified by the storage_loop_device_target variable. Here’s an example configuration:

   role:
     name: storage
     storage:
       loop_device:
         name: <LOOP_DEVICE_NAME>
         target: <LOOP_DEVICE_TARGET>
   

3. Create a role orchestration_architect.Storage.loop_device:

   `*<LOOP_DEVICE_STATE>*`: present | absent | info | offline | online
   

4. Ensure Storage Role Specifics: Add functor details to the loop_device role.
5. Deploy: Mount a btrfs subvolume in the ephemeral storage pool within tmpfs using nspawn.
6. Utilize copy-on-write Mechanisms: Design composable overlays with btrfs_subvolumes.

Playbook Steps

Pre-run Playbooks

Import a pre-run playbook to set up the environment:

- ansible.builtin.import_playbook: "../Meta/Setup_Environment"

Task Details

1. Prepare Var Assignments: Define key variables to be overridden if necessary.

   vars:
     container_collection: "Sandbox"
     container_name: "Container_ALPHA"
     ephemeral_base_path: "/mnt/orchestration_architect/ephemeral"
     ephemeral_storage_pool: "{{ ephemeral_base_path }}/{{ container_collection }}/storage_pool"
     ephemeral_storage_pool_size: 4G
     container_base_size: 2G
   

2. Create Ephemeral Storage Pool for Containers:

   • Create mount point for ephemeral storage pool.

   - name: Create Ephemeral Storage Pool for Containers
     include_role:
       name: storage
     vars:
       storage_mount_table:
         - source: tmpfs
           type: tmpfs
           options: "size={{ ephemeral_storage_pool_size }}"
           target: "{{ ephemeral_storage_pool }}"
           state: "mounted"
   

3. Create Volume Storage:

   • Directory creation for mount point and volume pool.
   • File creation for block device image.
   • Loop device setup.
   • btrfs filesystem configuration and subvolume creation.

   - name: Create Volume Storage
     tasks:
       - name: Create Ephemeral Storage Pool mount point
         ansible.builtin.file:
           path: "{{ ephemeral_mount_point }}"
           state: directory
           mode: '0700'
       - name: Create Ephemeral Storage Pool
         ansible.builtin.mount:
           path: "{{ ephemeral_mount_point }}"
           src: "tmpfs"
           fstype: "tmpfs"
           opts: "size={{ ephemeral_storage_pool_size }}"
           state: "mounted"
       - name: Create container volume pool mount point directory
         ansible.builtin.file:
           path: "{{ container_volume_pool_mount_point }}"
           state: directory
           mode: '0700'
           - name: Create file for volume collection block device image
         community.general.filesize:
           path: "{{ container_volume_pool_block_device_image }}"
           size: "{{ container_base_size }}"
       - name: Create loop device to expose the volume pool
         command: "losetup --find --nooverlap --show {{ container_volume_pool_block_device_image }}"
         register: loop_device_result
       - name: Generate Container Volumes
         ansible.builtin.include_role: "storage"
         vars:
           storage_loopback_device:
             name: "{{ oollection_name }}"
       - name: Create BTRFS filesystem on the loop device
         filesystem:
           path: "{{ loop_device_result.stdout }}"
           type: btrfs
           opts: "-n 16k"
       - name: Create BTRFS subvolume for @init
         command: btrfs subvolume create {{ container_volume_pool }}/@init
       - name: Create @base subvolume
         command: btrfs subvolume snapshot -r {{ container_volume_pool }}/@init {{ container_volume_pool }}/@base
       - name: Create @overlay subvolume for changes
         command: btrfs subvolume create {{ container_volume_pool }}/@overlay
   

4. Overlay and Initial Snapshot Configuration:

   • Directory configurations for overlay.
   • Initial snapshot creation.

   - name: Create overlay directories for nspawn
     ansible.builtin.file:
       path: "{{ ephemeral_storage_pool }}/overlay"
       state: directory
       mode: '0700'
   - name: Create initial snapshot for container
     command: btrfs subvolume snapshot {{ ephemeral_storage_pool }}/@base {{ ephemeral_storage_pool }}/@initial
   

5. Systemd-nspawn Container Setup:

   • Configuration and start of the systemd-nspawn container.

   - name: Configure systemd-nspawn container
     community.general.systemd_nspawn:
       name: arch_container
       image: "{{ container_volume_pool }}/@base"
       machine: "arch_sandbox_container"
       command: /bin/zsh
       state: started
       boot: false
   

System Managed Regions

• 01_File_Header This region is identified by the first --- marker matches the regex expression '^---$'
• 02_Managed_Region_Before_Content Managed block for pre-run steps. See meta_playbooks specification for more details.
• 04_Managed_Region_After_Content Managed block for post-run steps (currently empty).