Tutorials and stories from Relay, the DDD / CQRS / event-sourcing framework for .NET.https://relay.nuvoralabs.dev/https://relay.nuvoralabs.dev/articles/authorization/https://relay.nuvoralabs.dev/articles/authorization/Authorization in Relay is declared on the message, not the endpoint.https://relay.nuvoralabs.dev/articles/automated-blue-green-rebuilds/https://relay.nuvoralabs.dev/articles/automated-blue-green-rebuilds/Article 008 gave you the shadow (blue/green) rebuild: a projection implements IRebuildableProjection, IProjectionRebuildManager builds a fresh shadow read model from history while the live one keeps serving, and once the shadow has caught up an operator calls SwapAsync to atomically promote it.https://relay.nuvoralabs.dev/articles/caching-queries/https://relay.nuvoralabs.dev/articles/caching-queries/A read model (article 007) already makes queries fast — a single indexed SELECT.https://relay.nuvoralabs.dev/articles/concurrency-and-snapshots/https://relay.nuvoralabs.dev/articles/concurrency-and-snapshots/Article 005's event sourcing works beautifully for a fresh account with three events. Production breaks that idyll two ways.https://relay.nuvoralabs.dev/articles/crypto-shredding-right-to-erasure/https://relay.nuvoralabs.dev/articles/crypto-shredding-right-to-erasure/An event-sourced system has a property its operators love and its compliance officers fear: the log is immutable and never deletes.https://relay.nuvoralabs.dev/articles/distributed-coordination/https://relay.nuvoralabs.dev/articles/distributed-coordination/You scale a service by running more copies of it — but now those copies can step on each other: two instances run the same nightly job, or both try to advance the same projection, or process the same key out of order.https://relay.nuvoralabs.dev/articles/domain-events/https://relay.nuvoralabs.dev/articles/domain-events/In article 002 the Order aggregate raised domain events, but they just sat in a list — nothing reacted to them. This article closes that loop.https://relay.nuvoralabs.dev/articles/errors-and-http/https://relay.nuvoralabs.dev/articles/errors-and-http/A handler's job is to express what went wrong in business terms — "this payment was not found," "the amount exceeds the limit," "the card was declined" — not to know that those map to HTTP 404, 422, and 402.https://relay.nuvoralabs.dev/articles/event-archiving-and-compaction/https://relay.nuvoralabs.dev/articles/event-archiving-and-compaction/An event store is append-only: events are never updated and never deleted, which is exactly what makes it a trustworthy source of truth.https://relay.nuvoralabs.dev/articles/event-sourcing-basics/https://relay.nuvoralabs.dev/articles/event-sourcing-basics/Every sample so far stored state: the current product, the current order, the current balance.https://relay.nuvoralabs.dev/articles/fenced-leadership-and-membership/https://relay.nuvoralabs.dev/articles/fenced-leadership-and-membership/Article 023 elects a leader the simple way: a connection-bound ILeaderElector holds a PostgreSQL advisory lock for as long as its connection lives, and the database drops that lock when the process dies.https://relay.nuvoralabs.dev/articles/first-aggregate/https://relay.nuvoralabs.dev/articles/first-aggregate/In article 001 the Product was a plain record and the "store" was a dictionary.https://relay.nuvoralabs.dev/articles/getting-started/https://relay.nuvoralabs.dev/articles/getting-started/Relay is a framework for building .NET services around CQRS (Command Query Responsibility Segregation) and an in-process mediator.https://relay.nuvoralabs.dev/articles/inbox/https://relay.nuvoralabs.dev/articles/inbox/The outbox guarantees at-least-once delivery — which means the same message can arrive twice (a broker redelivery, an outbox re-publish after a crash).https://relay.nuvoralabs.dev/articles/inline-and-multistream-projections/https://relay.nuvoralabs.dev/articles/inline-and-multistream-projections/Article 007 built the standard read side: a projection runs in a background host, catches up from a checkpoint after each command commits, and is eventually consistent.https://relay.nuvoralabs.dev/articles/intra-projection-sharding/https://relay.nuvoralabs.dev/articles/intra-projection-sharding/Article 008 makes a deliberate promise: a projection has exactly one active worker.https://relay.nuvoralabs.dev/articles/messaging-and-transports/https://relay.nuvoralabs.dev/articles/messaging-and-transports/The outbox stages events; a transport carries them.https://relay.nuvoralabs.dev/articles/multi-tenancy/https://relay.nuvoralabs.dev/articles/multi-tenancy/A multi-tenant service serves many customers (tenants) from shared infrastructure while guaranteeing that one tenant can never see another's data.https://relay.nuvoralabs.dev/articles/observability/https://relay.nuvoralabs.dev/articles/observability/You cannot operate what you cannot see. Relay is instrumented with OpenTelemetry-native primitives out of the box — no wrappers, no proprietary format.https://relay.nuvoralabs.dev/articles/operational-event-queries/https://relay.nuvoralabs.dev/articles/operational-event-queries/The event store is an append-only log, and article 005 is emphatic about the rule that follows from that: never query the event store for reads.https://relay.nuvoralabs.dev/articles/outbox/https://relay.nuvoralabs.dev/articles/outbox/A command often needs to do two things: change its own state (save the order) and tell other services about it (publish OrderPlaced).https://relay.nuvoralabs.dev/articles/persistent-named-subscriptions/https://relay.nuvoralabs.dev/articles/persistent-named-subscriptions/A projection (article 007) is a catch-up reader: it walks the global event log forward, updates a read model, and remembers how far it got so a restart resumes instead of reprocessing two years of history.https://relay.nuvoralabs.dev/articles/pessimistic-aggregate-locking/https://relay.nuvoralabs.dev/articles/pessimistic-aggregate-locking/Article 006 established Relay's default for concurrent writes to an event-sourced aggregate: optimistic concurrency.https://relay.nuvoralabs.dev/articles/projection-operations/https://relay.nuvoralabs.dev/articles/projection-operations/Article 007's projection host works while every event is well-behaved. Production guarantees two things that break that assumption.https://relay.nuvoralabs.dev/articles/projections/https://relay.nuvoralabs.dev/articles/projections/Event sourcing stores what happened, which is perfect for the write side and useless for the read side.https://relay.nuvoralabs.dev/articles/recurring-jobs/https://relay.nuvoralabs.dev/articles/recurring-jobs/Article 018 scheduled one-shot future work. This article covers the recurring case — "every night at 2am," "every Monday," "every 15 minutes" — and the job as the unit of recurring/background work.https://relay.nuvoralabs.dev/articles/reference-architecture/https://relay.nuvoralabs.dev/articles/reference-architecture/The previous twenty-four articles each isolated one capability.https://relay.nuvoralabs.dev/articles/reliable-messaging/https://relay.nuvoralabs.dev/articles/reliable-messaging/The previous three articles built the pieces; this one assembles them into the complete, reliable, cross-service flow:https://relay.nuvoralabs.dev/articles/resiliency/https://relay.nuvoralabs.dev/articles/resiliency/Distributed systems fail in partial, transient ways: a database blips, a downstream API times out, a queue backs up.https://relay.nuvoralabs.dev/articles/rich-event-metadata/https://relay.nuvoralabs.dev/articles/rich-event-metadata/Every event Relay appends already carries a little metadata: the CommandName that produced it and a Timestamp.https://relay.nuvoralabs.dev/articles/routing-slips/https://relay.nuvoralabs.dev/articles/routing-slips/A distributed process books a flight, a hotel, and a car across three services. The flight and hotel succeed; the car fails.https://relay.nuvoralabs.dev/articles/sagas/https://relay.nuvoralabs.dev/articles/sagas/A command changes one aggregate; reliable messaging lets services react to each other.https://relay.nuvoralabs.dev/articles/scheduling/https://relay.nuvoralabs.dev/articles/scheduling/Some work shouldn't happen now — it should happen later: send a reminder in 30 minutes, expire an unpaid order in an hour, retry a failed call after a backoff.https://relay.nuvoralabs.dev/articles/schema-evolution/https://relay.nuvoralabs.dev/articles/schema-evolution/In an event-sourced system the events are the database, and unlike rows you can never UPDATE them — history is immutable.https://relay.nuvoralabs.dev/articles/standalone-courier-activities/https://relay.nuvoralabs.dev/articles/standalone-courier-activities/017 showed compensation inside a saga: forward legs record undo-commands onto a durable itinerary, and a failure replays them in reverse as reliable, scheduled commands.https://relay.nuvoralabs.dev/articles/state-machine-sagas/https://relay.nuvoralabs.dev/articles/state-machine-sagas/Article 015 authored a saga imperatively — handler methods that mutate state and call RequestTimeout/Complete.https://relay.nuvoralabs.dev/articles/time-travel-and-live-aggregation/https://relay.nuvoralabs.dev/articles/time-travel-and-live-aggregation/Event sourcing stores the sequence of events that produced an aggregate's state, and the write side rebuilds the current state by replaying that sequence (article 005).https://relay.nuvoralabs.dev/stories/how-a-tiny-team-shipped-like-a-big-one/https://relay.nuvoralabs.dev/stories/how-a-tiny-team-shipped-like-a-big-one/The payoff: five people, big-system guarantees, no army requiredhttps://relay.nuvoralabs.dev/stories/the-2am-page-nobody-could-read/https://relay.nuvoralabs.dev/stories/the-2am-page-nobody-could-read/Something's broken, the dashboard is green, and nobody can find the requesthttps://relay.nuvoralabs.dev/stories/the-500-that-leaked-the-stack-trace/https://relay.nuvoralabs.dev/stories/the-500-that-leaked-the-stack-trace/Inconsistent errors, leaked internals, and a partner who couldn't integratehttps://relay.nuvoralabs.dev/stories/the-account-that-went-negative/https://relay.nuvoralabs.dev/stories/the-account-that-went-negative/The "impossible" balance, because the rules lived in the UI, not the modelhttps://relay.nuvoralabs.dev/stories/the-auth-check-everyone-forgot/https://relay.nuvoralabs.dev/stories/the-auth-check-everyone-forgot/An endpoint shipped wide open, and the code review didn't catch ithttps://relay.nuvoralabs.dev/stories/the-black-friday-that-melted/https://relay.nuvoralabs.dev/stories/the-black-friday-that-melted/One slow dependency took down everything, then the retries finished the jobhttps://relay.nuvoralabs.dev/stories/the-case-of-the-missing-4000/https://relay.nuvoralabs.dev/stories/the-case-of-the-missing-4000/A balance is wrong and nobody can say why — there's no historyhttps://relay.nuvoralabs.dev/stories/the-customer-view-that-was-always-a-bit-wrong/https://relay.nuvoralabs.dev/stories/the-customer-view-that-was-always-a-bit-wrong/Stale-after-write reads and an incoherent multi-source dashboardhttps://relay.nuvoralabs.dev/stories/the-customer-who-asked-to-be-forgotten/https://relay.nuvoralabs.dev/stories/the-customer-who-asked-to-be-forgotten/An immutable log met the legal right to be erasedhttps://relay.nuvoralabs.dev/stories/the-email-that-sent-itself-five-times/https://relay.nuvoralabs.dev/stories/the-email-that-sent-itself-five-times/One event, delivered twice, charged the customer twicehttps://relay.nuvoralabs.dev/stories/the-field-we-forgot-to-add/https://relay.nuvoralabs.dev/stories/the-field-we-forgot-to-add/New code couldn't read three years of old, immutable eventshttps://relay.nuvoralabs.dev/stories/the-five-things-that-should-happen-when-money-moves/https://relay.nuvoralabs.dev/stories/the-five-things-that-should-happen-when-money-moves/One action did five jobs inline; a broken email stopped a deposithttps://relay.nuvoralabs.dev/stories/the-fraud-team-who-showed-up-late/https://relay.nuvoralabs.dev/stories/the-fraud-team-who-showed-up-late/A new consumer needed all of history, then live — without losing its placehttps://relay.nuvoralabs.dev/stories/the-log-that-ate-the-storage-budget/https://relay.nuvoralabs.dev/stories/the-log-that-ate-the-storage-budget/Keeping everything forever became the biggest line itemhttps://relay.nuvoralabs.dev/stories/the-nightly-job-that-quietly-stopped/https://relay.nuvoralabs.dev/stories/the-nightly-job-that-quietly-stopped/A cron job on one box died silently and lost two weeks of bookshttps://relay.nuvoralabs.dev/stories/the-onboarding-that-got-lost-in-if-statements/https://relay.nuvoralabs.dev/stories/the-onboarding-that-got-lost-in-if-statements/A workflow modeled as flag-soup, with impossible states in productionhttps://relay.nuvoralabs.dev/stories/the-order-that-got-stuck-forever/https://relay.nuvoralabs.dev/stories/the-order-that-got-stuck-forever/A five-step process died on step three and left money in limbohttps://relay.nuvoralabs.dev/stories/the-partner-who-spoke-a-different-language/https://relay.nuvoralabs.dev/stories/the-partner-who-spoke-a-different-language/Every new partner ran a different message brokerhttps://relay.nuvoralabs.dev/stories/the-payment-that-published-but-never-happened/https://relay.nuvoralabs.dev/stories/the-payment-that-published-but-never-happened/The database saved it but the message never sent — or vice versahttps://relay.nuvoralabs.dev/stories/the-payout-that-ran-twice/https://relay.nuvoralabs.dev/stories/the-payout-that-ran-twice/Redundancy without coordination paid every venue six timeshttps://relay.nuvoralabs.dev/stories/the-read-model-that-lied/https://relay.nuvoralabs.dev/stories/the-read-model-that-lied/A fixed bug's wrong numbers were stuck in the dashboard foreverhttps://relay.nuvoralabs.dev/stories/the-reminder-that-arrived-a-day-late/https://relay.nuvoralabs.dev/stories/the-reminder-that-arrived-a-day-late/A scan-and-send loop sent duplicates, gaps, and 3 a.m. emailshttps://relay.nuvoralabs.dev/stories/the-spreadsheet-that-ran-the-warehouse/https://relay.nuvoralabs.dev/stories/the-spreadsheet-that-ran-the-warehouse/Every feature takes longer than the last; the code has turned to souphttps://relay.nuvoralabs.dev/stories/the-tenant-who-saw-someone-elses-data/https://relay.nuvoralabs.dev/stories/the-tenant-who-saw-someone-elses-data/One forgotten WHERE clause became a customer-facing breachhttps://relay.nuvoralabs.dev/stories/the-ticket-page-that-hugged-the-database-to-death/https://relay.nuvoralabs.dev/stories/the-ticket-page-that-hugged-the-database-to-death/Going viral became an outage; lookers crowded out buyershttps://relay.nuvoralabs.dev/stories/the-transaction-feed-that-fell-behind/https://relay.nuvoralabs.dev/stories/the-transaction-feed-that-fell-behind/One sequential projection couldn't keep up on paydayhttps://relay.nuvoralabs.dev/stories/the-transfer-that-needed-undoing/https://relay.nuvoralabs.dev/stories/the-transfer-that-needed-undoing/A folder of one-off "undo money" scripts, none of them auditablehttps://relay.nuvoralabs.dev/stories/the-two-people-who-bought-the-last-seat/https://relay.nuvoralabs.dev/stories/the-two-people-who-bought-the-last-seat/Two buyers, one seat, a race condition in correct-looking codehttps://relay.nuvoralabs.dev/stories/what-did-my-balance-say-last-tuesday/https://relay.nuvoralabs.dev/stories/what-did-my-balance-say-last-tuesday/The payoff: customer, regulator, and lawyer all ask about the past — and get answershttps://relay.nuvoralabs.dev/stories/who-did-this-and-when/https://relay.nuvoralabs.dev/stories/who-did-this-and-when/The payoff: 5,000 mystery refunds, answered precisely from the log