Elixir Caddy

Start Caddy reverse proxy server in Elixir project.

Manage caddy configuration in Elixir.

Add this in deps in mix.exs to install

{:caddy, "~> 2.0"}

If caddy bin is set, caddy server will automate start when application start.

Start in extra_applications

def application do
  [
    extra_applications: [Caddy.Application]
  ]
end

• Notice

If caddy_bin is not specifiy, Caddy.Server will not start.

Set Caddy binary when needed.

Set caddy_bin to the path of Caddy binary file and start Caddy.Server.

Caddy.Config.set_bin("/usr/bin/caddy")
Caddy.restart_server()

This will restart server automatically

Caddy.Config.set_bin!("/usr/bin/caddy")

Config

import Config

# dump caddy server log to stdout
config :caddy, dump_log: false

# caddy server will not start, this is useful for testing
config :caddy, start: false

# configure caddy paths
config :caddy, :base_path, "/custom/caddy/path"
config :caddy, :etc_path, "/custom/etc/path"
config :caddy, :run_path, "/custom/run/path"
config :caddy, :tmp_path, "/custom/tmp/path"
config :caddy, :env_file, "/custom/path/envfile"
config :caddy, :pid_file, "/custom/path/caddy.pid"

Telemetry

The library includes comprehensive telemetry support for monitoring Caddy operations. Telemetry events are emitted for:

• Configuration changes: [:caddy, :config, :set], [:caddy, :config, :get], etc.
• Server lifecycle: [:caddy, :server, :start], [:caddy, :server, :stop]
• API operations: [:caddy, :api, :request], [:caddy, :api, :response]
• File operations: [:caddy, :file, :read], [:caddy, :file, :write]
• Validation: [:caddy, :validation, :success], [:caddy, :validation, :error]
• Adaptation: [:caddy, :adapt, :success], [:caddy, :adapt, :error]
• Logging operations: [:caddy, :log, :debug], [:caddy, :log, :info], [:caddy, :log, :warning], [:caddy, :log, :error]
• Log buffer/store: [:caddy, :log, :received], [:caddy, :log, :buffered], [:caddy, :log, :buffer_flush], [:caddy, :log, :stored], [:caddy, :log, :retrieved]

Logging with Telemetry

All logging operations emit telemetry events. By default, a handler automatically forwards log events to Elixir's Logger:

# Use telemetry-based logging (instead of Logger directly)
Caddy.Telemetry.log_debug("Server starting", module: MyApp)
Caddy.Telemetry.log_info("Configuration loaded", config_id: 123)
Caddy.Telemetry.log_warning("Deprecation warning", function: "old_api")
Caddy.Telemetry.log_error("Failed to connect", reason: :timeout)

Configure logging behavior:

config :caddy,
  attach_default_handler: true,  # Auto-forward logs to Logger (default: true)
  log_level: :info               # Minimum level to log (default: :debug)

Custom Telemetry Handlers

Attach custom handlers to process log events:

# Send errors to external monitoring service
:telemetry.attach("error_reporter", [:caddy, :log, :error],
  fn _event, _measurements, metadata, _config ->
    MyApp.ErrorReporter.report(metadata.message, metadata)
  end, %{})

# Monitor log buffer performance
:telemetry.attach("buffer_monitor", [:caddy, :log, :buffered],
  fn _event, measurements, _metadata, _config ->
    MyApp.Metrics.track_buffer_size(measurements.buffer_size)
  end, %{})

Usage Example

# Attach telemetry handler
:telemetry.attach_many("caddy_handler", [
  [:caddy, :config, :set],
  [:caddy, :server, :start],
  [:caddy, :log, :error]
], fn event_name, measurements, metadata, _config ->
  IO.inspect({event_name, measurements, metadata})
end, %{})

# Start telemetry poller for system metrics
Caddy.Telemetry.start_poller(30_000)

Available Functions

• Caddy.Telemetry.log_debug/2 - Emit debug log event
• Caddy.Telemetry.log_info/2 - Emit info log event
• Caddy.Telemetry.log_warning/2 - Emit warning log event
• Caddy.Telemetry.log_error/2 - Emit error log event
• Caddy.Telemetry.emit_config_change/3 - Configuration change events
• Caddy.Telemetry.emit_server_event/3 - Server lifecycle events
• Caddy.Telemetry.emit_api_event/3 - API operation events
• Caddy.Telemetry.list_events/0 - List all available events
• Caddy.Telemetry.attach_handler/3 - Attach telemetry handler
• Caddy.Telemetry.detach_handler/1 - Detach telemetry handler