Use app as the default service name

[unflxw]

Use app as the default service name

The collector turns the service name into names that customers see. A
trace's namespace becomes {service name}/{namespace}, so a web
request from an app that does not set service_name was filed under
unknown/web. A log line's group falls back to the service name on
its own, so those lines were grouped under unknown.

Leaving service_name unset is the normal case for an app that is a
single service. Nothing about it is actually unknown, so the fallback
now describes what it is. The revision and hostname fallbacks
still report unknown, because those are facts about the running
process that AppSignal really does not have.

Apply revision and host name fallbacks to None

The OpenTelemetry resource looks up revision and hostname with a
dictionary default, which only applies when the key is missing. Passing
either option as None puts the key in the config with a None value,
so the lookup returns that None and the resource builder drops the
attribute. The collector supplies its own revision when the attribute is
absent, but not its own host name, so an app configured with
hostname=None reported no host name at all.

[backlog-helper]

Hi @unflxw,

We've found some issues with your Pull Request.

• This Pull Request is missing labels. Please add labels to help identify types of Pull Requests. - (More info)

---

New issue guide | Backlog management | Rules | Feedback

[unflxw]

Rationale for this (and for consistency, its twin Ruby PR at appsignal/appsignal-ruby#1581) is to have the same name for customers who upgrade from agent mode to collector mode. @matsimitsu will be changing the processor's translation layer to use "app" as well, so we have a shared, reasonable enough default.

Docs will still advise setting a service name as part of collector mode setup, so the fallback may not be very relevant, but customers who upgrade somewhat manually may skip the docs.

[Copilot]

Pull request overview

Updates the OpenTelemetry default service name from unknown to app.

Changes:

• Changes the service-name fallback to app.
• Updates the corresponding test.
• Adds a patch changeset.

A moderate issue remains in src/appsignal/opentelemetry.py: Options(service_name=None) does not emit app because the present None value bypasses the dictionary fallback.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Summary
tests/test_config.py	Updates the expected default service name.
src/appsignal/opentelemetry.py	Changes the service-name fallback; requires a null-aware fallback for explicit None.
.changesets/default-service-name-to-app.md	Documents the patch release.

Suppressed comments (2)

src/appsignal/opentelemetry.py:293

• _resource is also used for the embedded-agent path: Client.start() calls start_opentelemetry after starting either the agent or the external collector, while service_name is explicitly collector-only in Config._warn_collector_exclusive_options (config.py:429-440). This unconditional fallback therefore changes the agent-mode resource as well, despite the changeset and description scoping the behavior to collector mode. Either gate the new fallback on config.should_use_collector() and preserve the existing agent-mode default, or broaden the documented scope and tests.

            "service.name": config.options.get("service_name", "app"),

tests/test_config.py:344

• This test builds Config(Options()), which has no collector endpoint and therefore exercises the agent path, but the changeset says the new fallback is collector-only. Since _resource is also used for agent tracer/metric providers, this assertion locks in behavior outside the stated scope and leaves the collector case untested. Either make this a collector config and add/retain an agent-mode assertion for "unknown", or update the changeset to describe a global change.

    assert resource.attributes["service.name"] == "app"

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

---

Replies from @unflxw, added with copilot-loop. Copilot's review above is unchanged.

src/appsignal/opentelemetry.py:293 — Dismissed. The service_name option only has an effect in collector mode, which is why Config._warn_collector_exclusive_options warns when it is set without a collector endpoint. The agent ignores the service.name resource attribute, so the value the resource carries in agent mode makes no difference to what a customer sees. The changeset describes where the change is visible, which is collector mode.

tests/test_config.py:344 — Dismissed. _resource builds the same attributes whichever mode is in use, so a test that does not set a collector endpoint still covers the fallback. There is no separate collector-mode behaviour to test here, and the value only reaches a customer in collector mode, which is what the changeset says.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/appsignal/opentelemetry.py:293

• This fallback is applied in agent mode as well as collector mode: _resource is used by _start_tracer and _start_metrics for both, while service_name is documented as collector-only in src/appsignal/config.py:430-441. That changes the agent-mode resource from unknown to app, contrary to the changeset's collector-only scope. Gate the app fallback on config.should_use_collector() (and retain unknown for agent mode), or update the documented behavior if the agent change is intentional.

            "service.name": config.options.get("service_name") or "app",

---

Replies from @unflxw, added with copilot-loop. Copilot's review above is unchanged.

src/appsignal/opentelemetry.py:293 — Dismissed, for the same reason as on the previous review. The service_name option only has an effect in collector mode, which is why Config._warn_collector_exclusive_options warns when it is set without a collector endpoint. The agent ignores the service.name resource attribute, so the value the resource carries in agent mode never reaches a customer. Gating the fallback on config.should_use_collector() would add a branch that no customer can observe. The changeset describes where the change is visible, which is collector mode.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.