Health Checks

Wallaby runs as a hosted background service on each node of a cluster. The Wallaby.AspNetCore.HealthChecks package exposes a health check so you can wire a liveness probe to a Wallaby worker.

Install & register

dotnet add package Wallaby.AspNetCore.HealthChecks

builder.Services.AddHealthChecks().AddWallaby();

The package only depends on Microsoft.Extensions.Diagnostics.HealthChecks, so it also works in a plain generic host if required.

The wallaby check

Registered as wallaby (tag wallaby). It reports:

• Unhealthy - When the CDC background service has terminated (faulted out of its hosted loop).
• Healthy - In every other state: a leader streaming changes, a standby waiting to take over, or a node still starting.

The check attaches a data dictionary for diagnostics: role, faulted, lastError, startedAt, leaderSince, lastAcknowledgedLsn, lastProgressAt, lastIngestionLagSeconds, consecutiveLeaderFailures, consecutiveFanoutFailures, slotName, and one lastSinkDeliveryAt:<sink> entry per sink that has accepted a batch this session. A nonzero consecutiveFanoutFailures means the fan-out worker is stuck retrying with backoff. Live replication keeps flowing, so the node stays Healthy, but the value is worth alerting on.

A climbing consecutiveLeaderFailures means the leader is crash-looping: sessions keep dying before a single transaction is fully delivered and acknowledged (e.g. a sink permanently rejecting a batch). The counter only resets on real progress or a clean step-down — not just because a failing session ran for a while first — so it is a reliable alerting signal even when each session streams briefly before failing.

::: WARNING The data dictionary can include exception text. Don't expose a detailed /health response on a public endpoint. :::

Reading status directly

The check reads a public IWallabyStatus singleton that the core runtime maintains in memory (role, leadership, last acknowledged LSN, last ingestion lag, leader-session failures, fault). AddWallaby registers it, so you can resolve IWallabyStatus and read Current to surface CDC status in your own diagnostics.

Readiness

A richer readiness check (graded on replication lag / retained WAL) may be added later. Lag is best watched through metrics (wallaby.ingestion.lag).