Configuration and Information Systems

Relevant source files

• api/swagger.yaml
• api/types/types.go
• daemon/cdi.go
• daemon/cluster/utils.go
• daemon/command/config.go
• daemon/command/httphandler.go
• daemon/command/httphandler_test.go
• daemon/command/options.go
• daemon/config/config.go
• daemon/config/config_linux.go
• daemon/config/config_linux_test.go
• daemon/config/config_test.go
• daemon/config/config_windows.go
• daemon/config/config_windows_test.go
• daemon/config/extensions.go
• daemon/daemon_linux.go
• daemon/daemon_linux_test.go
• daemon/daemon_test.go
• daemon/daemon_unsupported.go
• daemon/devices.go
• daemon/devices_amd_linux.go
• daemon/devices_linux.go
• daemon/devices_nonlinux.go
• daemon/devices_nvidia_linux.go
• daemon/devices_test.go
• daemon/extensions.go
• daemon/id.go
• daemon/info.go
• daemon/info_unix.go
• daemon/info_unix_test.go
• daemon/info_windows.go
• daemon/inspect.go
• daemon/internal/capabilities/caps.go
• daemon/internal/capabilities/caps_test.go
• daemon/internal/nri/logshim.go
• daemon/internal/nri/nri.go
• daemon/internal/nri/nri_test.go
• daemon/internal/opts/host_gateway_opts.go
• daemon/internal/opts/named_iplist_opts.go
• daemon/internal/opts/opts.go
• daemon/internal/opts/opts_test.go
• daemon/pkg/opts/nri_opts.go
• daemon/pkg/opts/nri_opts_test.go
• daemon/reload.go
• daemon/reload_test.go
• daemon/reload_unix.go
• daemon/reload_windows.go
• daemon/top_unix.go
• daemon/top_unix_test.go
• daemon/top_windows.go
• extpoints/servicegrpc/v0/servicegrpc.go
• extpoints/servicegrpc/v0/servicegrpc_test.go
• integration/build/build_traces_test.go
• integration/container/cdi_test.go
• integration/daemon/daemon_test.go
• integration/daemon/nri/nri_test.go
• integration/daemon/nri/testdata/test_plugin.go
• man/dockerd.8.md
• pkg/homedir/homedir.go
• pkg/homedir/homedir_linux.go
• pkg/homedir/homedir_others.go
• pkg/homedir/homedir_test.go
• vendor/github.com/moby/buildkit/client/connhelper/npipe/npipe.go
• vendor/github.com/moby/buildkit/client/connhelper/npipe/npipe_other.go
• vendor/github.com/moby/buildkit/client/connhelper/npipe/npipe_windows.go

This document covers the Docker daemon's configuration management, system information aggregation, and runtime reload capabilities. The configuration system handles loading, validating, merging, and reloading daemon configuration from multiple sources (daemon.json and CLI flags). The information system collects comprehensive data about the host system, runtime environment, container device interfaces (CDI), network runtime interfaces (NRI), and daemon state for API clients and debugging.

For information about the broader daemon architecture and lifecycle, see Docker Daemon Core. For details about how these systems integrate with the API layer, see API Server and Endpoints.

Configuration Sources and Loading

The Docker daemon accepts configuration from two primary sources: configuration files (typically JSON format) and command-line flags. The system provides sophisticated merging and conflict resolution between these sources via the config.Config struct and the MergeDaemonConfigurations function.

Configuration Loading Flow

The loading process ensures that flags take precedence over file settings while detecting explicit conflicts using findConfigurationConflicts.

Sources: daemon/config/config.go449-466 daemon/config/config.go471-568 daemon/config/config.go688-777

Configuration File Processing

The daemon supports JSON configuration files with specialized Unicode handling (including Byte Order Marks) and validation implemented in daemon/config/config.go.

Component	Code Entity	Purpose
Parser	getConflictFreeConfiguration	Decodes JSON and tracks which keys were explicitly set.
Conflict Finder	findConfigurationConflicts	Compares ValuesSet from JSON against pflag.FlagSet.
Migration	migratedNamedConfig	Maps legacy keys (e.g., host-gateway-ip) to new structures.
Validation	Validate	Performs semantic checks on the merged result.

Sources: daemon/config/config.go477-505 daemon/config/config.go570-584 daemon/config/config.go125-131 daemon/config/config.go688-777

Configuration Structure

The daemon configuration is organized into a hierarchical structure with platform-specific and common components, defined primarily in daemon/config/config.go and extended in daemon/config/config_linux.go or daemon/config/config_windows.go.

Core Configuration Hierarchy

Sources: daemon/config/config.go181-301 daemon/config/config_linux.go70-97 daemon/config/config_windows.go37-45

Conflict Resolution Maps

The configuration package uses several static maps to control validation behavior:

• skipDuplicates: Options like runtimes that can exist in both flags and files without failing duplication checks daemon/config/config.go116-118
• flatOptions: Keys that must not be parsed as deep structures (e.g., log-opts, features) daemon/config/config.go84-93
• skipValidateOptions: Options like min-api-version that lack corresponding CLI flags daemon/config/config.go98-108

Sources: daemon/config/config.go84-123

Runtime Configuration Reload

The daemon supports reloading specific configuration options without a process restart via Daemon.Reload(conf *config.Config) daemon/reload.go91-139 This is managed transactionally using a two-phase commit protocol implemented by reloadTxn.

Reload Pipeline Architecture

Sources: daemon/reload.go33-58 daemon/reload.go91-139

Reloadable Options Implementation

Function	Code Entity	Logic
reloadDebug	Daemon.reloadDebug	Updates newCfg.Debug and adjusts logger levels daemon/reload.go152-162
reloadMaxConcurrentDownloadsAndUploads	Daemon.reloadMaxConcurrentDownloadsAndUploads	Resets defaults, updates imageService config via OnCommit daemon/reload.go164-190
reloadLabels	Daemon.reloadLabels	Overwrites newCfg.Labels dynamically.
reloadRegistryConfig	Daemon.reloadRegistryConfig	Updates mirror and insecure registry parameters.
reloadNRI	Daemon.reloadNRI	Reconfigures Node Resource Interface (NRI) integration parameters.

Sources: daemon/reload.go115-129 daemon/reload.go152-190

System Information Aggregation

The SystemInfo and SystemVersion methods defined in daemon/info.go aggregate system specifications from subsystems, image services, and host introspection utilities.

Information Data Flow

Sources: daemon/info.go44-101 daemon/info.go121-174

System Capability Detection (pkg/sysinfo)

The host inspection relies heavily on pkg/sysinfo to query Linux kernel features and cgroup controllers.

Probed Feature	Code Entity / Implementation
Cgroups v1/v2	Detects unified mode via cgroups.Mode() pkg/sysinfo/sysinfo_linux.go91-95
Memory Limits	Probes memory.max or memory.limit_in_bytes pkg/sysinfo/sysinfo_linux.go131-155
CPU Scheduling	Probes cpu.cfs_quota_us and cpu.shares pkg/sysinfo/sysinfo_linux.go158-179
Security Modules	Inspects /sys/kernel/security for AppArmor and Seccomp profiles pkg/sysinfo/sysinfo_linux.go105-106

Sources: pkg/sysinfo/sysinfo.go7-49 pkg/sysinfo/sysinfo_linux.go90-128

CDI and NRI Integration

The daemon incorporates advanced extension mechanisms such as Container Device Interface (CDI) and Node Runtime Interface (NRI).

• CDI Spec Dirs: Configured via CDISpecDirs in config.Config and populated in system.Info through daemon.fillDiscoveredDevicesFromDrivers daemon/info.go79 daemon/info.go98
• NRI Integration: Managed via daemon.nri, providing runtime hooks and configuration state exposed through daemon.nri.GetInfo() during system information aggregation daemon/info.go80

Sources: daemon/info.go79-80 daemon/info.go98 daemon/config/config.go257

Platform-Specific Info Filling

Platform-specific capabilities are injected into system information structs via fillPlatformInfo.

• Linux: Populates cgroup versions (v1 vs v2), memory/swap limit flags, oom kill flags, and commit hashes for runc, containerd, and init binaries daemon/info_unix.go26-76
• Warnings: Automatically generates user-facing warnings if features like IPv4 forwarding are disabled or if mandatory resource limits are missing from the host kernel daemon/info_unix.go81-159

Sources: daemon/info_unix.go26-161 daemon/info_unix.go163-183