Error Reporting

Lemon ships an optional Sentry sink for unhandled exceptions and process crashes, wired through lemon_core (present in every release profile).

Enabling it

Set SENTRY_DSN in the environment before boot:

export SENTRY_DSN="https://<public_key>@<org>.ingest.sentry.io/<project_id>"

Optional companions:

• LEMON_ENV (or SENTRY_ENVIRONMENT) — reported as the Sentry environment_name. Falls back to the Mix environment (e.g. "prod") if neither is set.

When SENTRY_DSN is absent or blank, nothing is configured: the :sentry application still boots (it's an optional dependency of lemon_core, and the release profiles include it), but with dsn: nil, which is Sentry's own documented "disabled" mode — no events are sent and no logger handler is attached. This is the default, and is what CI, tests, and local development run with.

:sentry and its HTTP client :finch are optional deps, so a host application that depends on lemon_core without them still boots: config/runtime.exs skips this block when Sentry.LoggerHandler is not loadable, and LemonCore.Application drops any configured handler whose module is missing.

What gets captured

Once enabled, a Sentry.LoggerHandler is attached at lemon_core boot (see LemonCore.Application.start/2, which calls Logger.add_handlers(:lemon_core)). With the handler's default capture_log_messages: false, it reports crashes — messages whose metadata carries an exit reason and stacktrace (unhandled exceptions, supervisor-reported process crashes) — at :error level and above. Routine Logger.error/2 calls that aren't crashes are not forwarded, so enabling this does not turn every logged error into a Sentry event.

The release/version tag on reported events comes from Application.spec(:lemon_core, :vsn) (the lemon_core app version, which tracks the umbrella's mix.exs version).

To capture something manually outside of a crash:

try do
  risky_operation()
rescue
  exception -> Sentry.capture_exception(exception, stacktrace: __STACKTRACE__)
end

Implementation

• Dependencies: apps/lemon_core/mix.exs adds {:sentry, "~> 13.0"} and {:finch, "~> 0.21"} (Sentry's default HTTP client since v12; the built-in JSON module is used on Elixir 1.19, so no separate JSON dependency is needed).
• Gating and configuration: config/runtime.exs sets config :sentry, ... and the :lemon_core, :logger handler entry only when SENTRY_DSN is present.
• Handler attachment: LemonCore.Application.start/2 calls Logger.add_handlers(:lemon_core), which is a no-op when nothing is configured under :lemon_core, :logger.