For external dependencies that are additive (e.g., mirrors/archives) rather than required for correctness, prefer fail-open behavior: log errors and continue operating using the primary source of truth. Reserve fail-fast for dependencies that are hard requirements for correctness or API functionality.

Practical rules:

• Classify each dependency/feature as either:
  • Critical (correctness-gating): if unavailable at startup or runtime, fail fast (or reject requests) to avoid silently incorrect behavior.
  • Additive (mirror/archive/log sink): if unavailable, continue core writes/operations; record the error for observability.
• Ensure the primary store remains the source of truth (e.g., DB-only audit logging still works).
• At startup and during batch flushes:
  • Catch connection/unreachability errors.
  • Log + emit metrics.
  • Do not block startup or request handling.
• Document the policy difference explicitly so teams don’t “standardize” into the wrong behavior.

Example (non-blocking additive sink):

onStartup():
  try:
    objectStoreClient = connect(config.objectStorage)
    archivalEnabled = true
  catch err:
    log.error("object storage unreachable; continuing database-only", err)
    archivalEnabled = false

writeAuditEvent(event):
  dbWrite(event) // must always succeed for correctness

flushBatch(batch):
  if not archivalEnabled: return
  try:
    objectStore.put(renderKey(batch), gzip(jsonl(batch)))
  catch err:
    log.error("archival upload failed; audit DB write already committed", err)
    // do not fail request handling