fix(legacy_openedx): keep the code location loadable when Vault is down

[blarghmatey]

What are the relevant tickets?

Sentry: DAGSTER-F

Description (What does it do?)

Part of a set of PRs working through the Sentry backlog from #2518.

This issue logged only one event, which badly understates it: mechanism: excepthook, handled: no, on the dagster-user-code-...-legacy-openedx pod. It is not a step failure — it is the gRPC server for the whole code location failing to start.

_job_default_config returns a default run config so the launchpad is pre-populated for ad-hoc runs, and is written to degrade gracefully when Vault is unreachable at load time. On that degraded path it returned {}:

if not vault_authenticated:
    return {}

But config={} does not mean "no default". Dagster treats any mapping as a default run config and validates it against the job's schema, so an empty one fails:

DagsterInvalidConfigError: Error in config when building job 'residential_edx_course_pipeline':
  Missing required config entries ['ops', 'resources'] at the root.

That validation runs inside build_caching_repository_data_from_list → job.partitions_def → _resolve_configs, i.e. while the repository is being constructed. So the fallback meant to keep the location alive was the thing killing it — and it takes down all three jobs and all three schedules, not just the residential one named in the message.

Returning None skips default-config validation entirely and leaves the launchpad unpopulated, which is the degraded behaviour the function was written to provide.

How can this be tested?

Reproduced directly, with Vault pointed at a closed port so authenticate_vault fails fast:

cd dg_projects/legacy_openedx
VAULT_ADDR=http://127.0.0.1:1 VAULT_ADDRESS=http://127.0.0.1:1 DAGSTER_ENVIRONMENT=qa \
  uv run python -c "import legacy_openedx.definitions as d; d.defs.get_repository_def()"

• Before: DagsterInvalidConfigError: ... missing required fields or contains invalid entries
• After: repository OK: 3 jobs

Note the failure does not reproduce on plain import — it needs the repository construction step, which is what the gRPC server does at startup.

Both cases are covered by the new legacy_openedx_tests/test_definitions.py (this code location had no tests before):

cd dg_projects/legacy_openedx && uv run pytest legacy_openedx_tests/ -q
# 2 passed

pre-commit run --files <changed> is clean.

Additional Context

Worth confirming after deploy that the legacy_openedx location is actually up in production — the single Sentry event suggests it crashed once rather than crash-looping, which would mean it came back when Vault recovered and this is a latent trap rather than a current outage. The mitxonline_edx_course_pipeline run in DAGSTER-E four minutes earlier indicates the location was healthy immediately before.

[Copilot]

Pull request overview

Keeps the legacy_openedx Dagster code location loadable when Vault is unavailable.

Changes:

• Returns None instead of an invalid empty default configuration.
• Adds regression tests for degraded repository loading.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
legacy_openedx/definitions.py	Corrects graceful default-config fallback behavior.
legacy_openedx_tests/test_definitions.py	Tests repository loading without Vault.

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