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Device Prerequisites

This page outlines the hardware and storage requirements for devices to run containerized applications.

Flash Layout Requirements

To support containerized applications, devices must have the following dedicated writeable flash partitions with minimum sizes and mount points as specified:

Partition Minimum Size Mount Point Purpose Writable
App Storage 256 MB /apps/packages Stores downloaded application packages (Deployment Units) Yes
App Data 128 MB /apps/data Stores persistent application data Yes
App Logs 20 MB /apps/logs Stores application log files Yes

Partition Structure

The recommended flash structure uses a dedicated /apps partition separate from the root filesystem:

/apps/                      # Dedicated partition for applications
├── packages/               # Application packages (Deployment Units)
├── data/                   # Persistent application data
│   └── <app-id>/           # Per-application data directory using obfuscated ID for security
└── logs/                   # Application logs
    └── <app-id>/           # Per-application logs directory using obfuscated ID for security

Root Filesystem Protection

It is generally safe to keep the root filesystem (rootfs) untouched. Using SquashFS for the root filesystem is recommended to maintain system integrity and reliability.

Thus, a dedicated partition in the device flash for storing applications outside of rootfs is mandatory. This separation provides:

  • Isolation: Applications cannot corrupt the root filesystem
  • Recovery: "Restore to default" operations can safely erase the apps partition without affecting the base image
  • Security: Application storage can be secured independently from the system partition
  • Write Permissions: Only applies to the apps partition, not to the base image.

Storage Requirements

Minimum Flash Space

The device must allocate sufficient flash space for the /apps partition based on:

  • Expected number of applications
  • Average application size
  • Data storage requirements per application
  • Log retention policies

Per-Application Quotas

Flash space quotas per application should be implemented to:

  • Prevent a single application from consuming excessive space (e.g., 90% of the partition)
  • Ensure fair resource allocation across applications
  • Maintain system stability and performance

Quota Policy

The definition and enforcement of per-application storage quotas in the data model is under discussion. Check the Data Models page for updates on quota configuration.

Security Requirements

Application Storage Security

The /apps folder and its contents must be secured to prevent unauthorized access and malicious activity:

  1. Encryption or Alternative Security: The /apps/ folder must be secured via encryption or other good security practices
  2. Data Integrity: Prevent spoofing or tampering with application packages and data
  3. Access Controls: Implement appropriate permissions to restrict application access

Application Data Isolation

Each application should store its data in a dedicated subdirectory:

/apps/data/<app-id>/        # Per-application data directory using obfuscated IDs

This isolation ensures:

  • Applications cannot identify other applications' partitions
  • Applications cannot access other applications' data
  • Data cleanup is straightforward when removing an application
  • Quota enforcement can be applied per application

Restore to Factory Behavior

During a "Factory Restore" operation:

  • The apps partition should be erased, removing all installed applications and their data, and returning the device to a clean state for app reinstallation.
  • The base squashfs image must remain intact, preserving the root filesystem.

This behavior ensures that factory reset operations are safe and predictable.