feat(deployment): add sd_notify integration with watchdog support

[newtonne]

Summary

Adds systemd sd_notify integration to Vector, enabling enhanced service lifecycle management when running under systemd with Type=notify.

Vector now sends:

• READY=1 when fully started and ready to process events
• STOPPING=1 at the beginning of graceful shutdown
• WATCHDOG=1 keepalive pings at half the configured WatchdogSec interval

The bundled vector.service and hardened-vector.service unit files are updated to use Type=notify, with an optional commented out WatchdogSec directive.

See: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html

Vector configuration

No config changes required.

How did you test this PR?

• Tested manually on Linux with a systemd unit using Type=notify:
  • Verified READY=1 is sent after startup is completed
  • Verified STOPPING=1 is sent on systemctl stop
  • Verified WATCHDOG=1 pings are sent at the correct interval with WatchdogSec enabled
• Verified all notify calls are no-ops when NOTIFY_SOCKET is not set, such as:
  • Unit tests
  • systemd unit using the default Type=simple
  • Standalone binary

Before

2026-03-30T18:31:00.008911+00:00 systemd[1]: Starting vector.service - Vector...
...
2026-03-30T18:31:00.048406+00:00 systemd[1]: vector.service: Changed start-pre -> running
2026-03-30T18:31:00.048599+00:00 systemd[1]: vector.service: Job 11673 vector.service/start finished, result=done
2026-03-30T18:31:00.048886+00:00 systemd[1]: Started vector.service - Vector.
...
2026-03-30T18:31:00.069751+00:00 vector[13987]: 2026-03-30T18:31:00.068889Z  INFO vector::app: Log level is enabled. level="info"
2026-03-30T18:31:00.069751+00:00 vector[13987]: 2026-03-30T18:31:00.069647Z  INFO vector::app: Loading configs. paths=["/etc/vector/vector.yaml"]
2026-03-30T18:31:00.074214+00:00 vector[13987]: 2026-03-30T18:31:00.074159Z  INFO vector::topology::running: Running healthchecks.
2026-03-30T18:31:00.074812+00:00 vector[13987]: 2026-03-30T18:31:00.074522Z  INFO vector::topology::builder: Healthcheck passed.
2026-03-30T18:31:00.074812+00:00 vector[13987]: 2026-03-30T18:31:00.074674Z  INFO vector: Vector has started. debug="false" version="0.54.0" arch="x86_64" revision="2b8b875 2026-03-10 15:47:37.284215410"
2026-03-30T18:31:00.074812+00:00 vector[13987]: 2026-03-30T18:31:00.074692Z  INFO vector::app: API is disabled, enable by setting `api.enabled` to `true` and use commands like `vector top`.

Note that systemd shows vector as started as soon as the process has forked.

After

2026-03-30T18:27:30.884285+00:00 systemd[1]: Starting vector.service - Vector...
...
2026-03-30T18:27:30.943735+00:00 vector[13467]: 2026-03-30T18:27:30.943609Z  INFO vector::app: Log level is enabled. level="info"
2026-03-30T18:27:30.945571+00:00 vector[13467]: 2026-03-30T18:27:30.945477Z  INFO vector::app: Loading configs. paths=["/etc/vector/vector.yaml"]
2026-03-30T18:27:30.964246+00:00 vector[13467]: 2026-03-30T18:27:30.964157Z  INFO vector::topology::running: Running healthchecks.
2026-03-30T18:27:30.965250+00:00 vector[13467]: 2026-03-30T18:27:30.964605Z  INFO vector::topology::builder: Healthcheck passed.
2026-03-30T18:27:30.965250+00:00 vector[13467]: 2026-03-30T18:27:30.965080Z  INFO vector: Vector has started. debug="true" version="0.55.0" arch="x86_64" revision=""
2026-03-30T18:27:30.965368+00:00 systemd[1]: vector.service: Got notification message from PID 13467 (READY=1)
2026-03-30T18:27:30.965406+00:00 systemd[1]: vector.service: Changed start -> running
2026-03-30T18:27:30.965421+00:00 systemd[1]: vector.service: Job 11079 vector.service/start finished, result=done
2026-03-30T18:27:30.965453+00:00 systemd[1]: Started vector.service - Vector.

But now systemd shows vector as started only after vector has finished starting up.

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Changelog fragment added: changelog.d/systemd_notify.feature.md
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

• Please read our Vector contributor resources.
• Do not hesitate to use @vectordotdev/vector to reach out to us regarding this PR.
• Some CI checks run only after we manually approve them.
  • We recommend adding a pre-push hook, please see this template.
  • Alternatively, we recommend running the following locally before pushing to the remote branch:
    • make fmt
    • make check-clippy (if there are failures it's possible some of them can be fixed with make clippy-fix)
    • make test
• After a review is requested, please avoid force pushes to help us review incrementally.
  • Feel free to push as many commits as you want. They will be squashed into one before merging.
  • For example, you can run git merge origin master and git push.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run make build-licenses to regenerate the license inventory and commit the changes (if any). More details on the dd-rust-license-tool.

[github-actions]

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[newtonne]

I have read the CLA Document and I hereby sign the CLA