fleet/docs/Contributing/architecture/software/software-installation.md

# Software installation architecture

This document provides an overview of Fleet's software installation architecture.

## Introduction

Software installation in Fleet enables the deployment and installation of software packages across
the device fleet. This document provides insights into the design decisions, system components, and
interactions specific to the Software Installation functionality.

## Important concepts

### Software types

Fleet supports 3 different types of installable software: custom packages, Fleet-maintained apps,
and VPP apps.

#### Custom packages

Custom packages are software packages whose installer is uploaded directly to Fleet by an admin.

Fleet supports `.pkg`, `.msi`, `.exe`, `.deb.`, and `.rpm` installers for custom packages.

#### Fleet-maintained apps

Fleet-maintained apps are software that Fleet curates. Fleet sources installers and generates
install and uninstall scripts for Fleet-maintained apps, so that admins can add them to their
software library with just a few clicks.

#### VPP apps

VPP apps are apps that can be added using Apple's Volume Purchasing Program functionality. These
apps are only for Apple devices (macOS, iOS, and iPadOS) and are managed using the Apple MDM protocol.

## Architecture overview

## Key components

## Architecture diagram

### VPP app install verification

Fleet verifies VPP app installs by sending a series of `InstalledApplicationList` MDM commands after
the acknowledgment of the `InstallApplication` command. It attempts to verify until either
- the app shows up in the `InstalledApplicationList` response as installed, or
- the verification timeout (defaults to 10m, configurable via the `FLEET_SERVER_VPP_VERIFY_TIMEOUT`
  env var).


```mermaid
sequenceDiagram
    autonumber
    Fleet->>+Host: InstallApplicationCommand
    Host-->>-Fleet: Acknowledged

    Fleet->>+Fleet: Start timeout

    loop Verification loop
        Fleet->>+Host: InstalledApplicationListCommand
        Host-->>-Fleet: Acknowledged<br/>[list of apps]
        critical Check app status
        option app in list, installed, exit:
            Fleet->>+Fleet: Move status to "Installed"
        option app not in list, timeout:
            Fleet->>+Fleet: Move status to "Failed"
        end
    end
```

## Installation flow

### Orbit implementation of installer-based (custom packages, FMA) software install

```mermaid
graph TD
    subgraph "Orbit software installation flow"
        direction TB
        A_Start((Start)) -->  B{"Check if install requested<br/>(Orbit config receiver)"};
        B -- 30s --> B
        B -- Yes --> C[GET installer details];
        C --> Err1[error/timeout: retry];
        Err1 --> A_Start;
        C --> D["Create temp dir (os.MkdirTemp)"];
        D --> E{CDN configured?}
        E -- Yes --> F[Download installer<br/>from CDN to temp dir]
        E -- No --> G[Download from Fleet]
        G --> Err3{Err?}
        Err3 -- Yes --> K
        Err3 -- No --> H
        F --> Err2{Err?}
        Err2 -- Yes --> G
        Err2 -- No --> H[Write install script to temp dir]
        H --> I["Run install script <br/> (timeout 1h)"]
        I --> J{Failure?}
        J -- Yes --> K[Delete temp dir]
        K --> L["POST script result <br/> (5 retries w/ backoff)"]
        J -- No --> M{Post-install<br/>script exists?}
        M -- Yes --> N[Write post-install<br/>script to temp dir]
        N --> O["Run post-install<br/>script (timeout 1hr)"]
        O --> P{Failure?}
        P -- Yes --> Q[Write uninstall script to temp dir]
        Q --> R["Run uninstall script<br/>(timeout 1hr)"]
        R --> K
        P -- No --> K
        M -- No --> K
    end
```

## Platform-specific implementations

### macOS

### Windows

### Linux

### iOS/iPadOS 

### Android

## Related resources

- [Software product group documentation](../../product-groups/software/) - Documentation for the Software product group
- [Software development guides](../../guides/software/) - Guides for Software development