SecretsGrpcHubClientOptions gains a getter-only FallbackEndpoints list:
additional hub addresses tried in order when a call fails with a
transport-level RpcException. Validation fails startup on blank/relative
entries and on any duplicate of the primary or another fallback (a
duplicated endpoint silently halves the configured failover).
New FailoverSecretsHubReader composes one GrpcSecretsHubClient per
endpoint: the answering endpoint is sticky (a sweep is GetManifest + N
GetSecrets batches — without stickiness every call after a primary
outage re-pays a full CallDeadline before reaching the healthy
fallback), rotation wraps so a recovered primary is retried when the
stuck-to endpoint fails, only RpcException triggers failover
(cancellation and defects propagate untouched), and when every endpoint
fails the last RpcException is rethrown so the sweep degrades to
last-known-good exactly as today. Failover warnings name only the two
endpoint URIs and the status code — never any credential material.
DI: zero fallbacks keeps the registration graph byte-identical to 0.4.x
(single keyed channel under ChannelServiceKey, plain
GrpcSecretsHubClient); with fallbacks, one container-owned keyed channel
per endpoint (fallback i under "{ChannelServiceKey}:fallback:{i}") wired
into the failover reader. GrpcSecretsHubClient itself is unchanged.
Safe only when every listed endpoint serves the SAME store — for
ScadaBridge, the central pair over one shared SQL Server store; the
options doc and CHANGELOG carry the warning.
Claude-Session: https://claude.ai/code/session_014WNM4vjoVksyyBraTXSZE1
Joseph Doherty
0d4978953f