Installer

Active contributors: Arthur Bellal, Baptiste Foy, Raphael Gavache

Purpose

The Datadog Installer is the binary that manages Agent installation, upgrade, rollback, and configuration on a host. It enables remote-controlled deployment from the Datadog backend: the customer installs the installer once, then receives Agent (and other Datadog software) upgrades over Remote Config without manual intervention.

The installer also installs non-Agent Datadog software where applicable, including the OTel agent, the Database Monitoring software, and APM injection libraries.

Directory layout

cmd/installer/
├── main.go
├── command/
├── subcommands/        # install, remove, upgrade, status, ...
├── user/               # Privileged user resolution
├── windows_resources/
└── BUILD.bazel

pkg/fleet/              # The bulk of installer logic
├── env/
├── installer/          # Core install/upgrade/rollback engine
├── ipc/
├── packages/           # Per-package handlers (agent, otel, ddot, …)
├── telemetry/
└── ...

cmd/agent/installer.go  # The core agent's hook into the installer (downstream)

Subcommands

Subcommand	Purpose
bootstrap	Bootstrap a new install.
install <package>	Install a specific Datadog package.
remove <package>	Uninstall a package.
purge	Remove all packages and the installer itself.
setup	Run post-install setup (systemd unit installation, etc.).
daemon	The long-running daemon (handles Remote Config push and lifecycle).
status	Status snapshot.
is-installed	Test whether a given package is present.
migrate-policies	Migrate older config policy formats.

The full list lives in cmd/installer/subcommands/.

Architecture

graph LR
    RC[Remote Config<br/>Datadog backend] -->|policies| DAEMON[installer daemon]
    DAEMON -->|install/upgrade| ENGINE[Engine<br/>pkg/fleet/installer]
    ENGINE -->|os-specific actions| OS[apt / dnf / msiexec / pkg]
    ENGINE -->|writes config| CONFIG[/etc/datadog-agent]
    AGENT[Datadog Agent] -. status / config events .-> ENGINE

The installer keeps a versioned set of installed packages on disk under /opt/datadog-packages/ (or the equivalent on the platform) and switches the running version by manipulating symlinks. This enables atomic upgrade and rollback.

Package handlers

pkg/fleet/packages/ implements per-package install/remove/configure handlers. Examples:

• agent/ — the Datadog Agent itself.
• otel/, ddot/ — the OpenTelemetry Collector flavor.
• apm-inject — APM auto-injection library.
• dbm-jdbc — Database Monitoring agent helpers.

Each handler implements the same interface so the engine can drive any package the same way.

Telemetry

pkg/fleet/telemetry/ ships installer events and metrics back to Datadog so customers can see install/upgrade history in the Fleet Automation UI.

Windows specifics

Windows installations use MSI packages; the installer wraps msiexec rather than handling install steps directly. Windows-specific code lives in cmd/installer/windows_resources/ and conditional _windows.go files. There is dedicated logic in pkg/fleet/installer/install_windows.go and the install_msi package family.

A recent example bug fix (fix(installer): retry rename on Windows for transient access-denied errors, PR #50028) is illustrative of the platform-specific issues the installer routinely deals with.

Key abstractions

Type / package	Location	Purpose
Installer	pkg/fleet/installer/installer.go	The install/upgrade engine
Repositories	pkg/fleet/installer/repository/	Versioned on-disk package store
Daemon	pkg/fleet/daemon/	Long-running lifecycle daemon
RemoteConfig	pkg/fleet/installer/rcaction.go	RC-driven actions

Entry points for modification

• Adding a new package handler: implement pkg/fleet/packages/<name>/ mirroring the existing handlers.
• Adding a new subcommand: copy from cmd/installer/subcommands/ and register.
• Changing the on-disk layout: ripple through pkg/fleet/installer/repository/ and the per-platform install code.

Related pages

• Apps: Agent — the most-installed package.
• Systems: Remote Config — how the backend reaches the installer.