HTTP Liveness Probe Stopgap Fix

.changeset/warm-coins-wave.md

@@ -0,0 +1,5 @@
+---
+'@powersync/service-core': patch
+---
+
+Minor improvement to the HTTP liveness probe. The liveness probe will return an HTTP `200` response code when running in the `API` mode. Any HTTP response in the `API` mode indicates the service is running. When running in the `UNIFIED` mode the HTTP response code is `200` if the last `touched_at` timestamp value is less than 10 seconds ago - this indicates the replication worker is running.

packages/service-core/src/routes/endpoints/probes.ts

@@ -25,11 +25,27 @@ export const startupCheck = routeDefinition({
 export const livenessCheck = routeDefinition({
   path: ProbeRoutes.LIVENESS,
   method: router.HTTPMethod.GET,
-  handler: async () => {
+  handler: async (params) => {
     const state = container.probes.state();
 
+    /**
+     * The HTTP probes currently only function in the API and UNIFIED
+     * modes.
+     *
+     * For the API mode, we don't really touch the state, but any response from
+     * the request indicates the service is alive.
+     *
+     * For the UNIFIED mode we update the touched_at time while the Replicator engine is running.
+     * If the replication engine is present and the timeDifference from the last
+     * touched_at is large, we report that the service is not live.
+     *
+     * This is only an incremental improvement. In future these values should be configurable.
+     */
+
+    const isAPIOnly = !params.context.service_context.replicationEngine;
     const timeDifference = Date.now() - state.touched_at.getTime();
-    const status = timeDifference < 10000 ? 200 : 400;
+
+    const status = isAPIOnly ? 200 : timeDifference < 10000 ? 200 : 400;
 
     return new router.RouterResponse({
       status,

packages/service-core/test/src/routes/probes.integration.test.ts

@@ -1,10 +1,10 @@
-import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
-import Fastify, { FastifyInstance } from 'fastify';
 import { container } from '@powersync/lib-services-framework';
-import * as auth from '../../../src/routes/auth.js';
-import * as system from '../../../src/system/system-index.js';
+import Fastify, { FastifyInstance } from 'fastify';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { configureFastifyServer } from '../../../src/index.js';
+import * as auth from '../../../src/routes/auth.js';
 import { ProbeRoutes } from '../../../src/routes/endpoints/probes.js';
+import * as system from '../../../src/system/system-index.js';
 
 vi.mock('@powersync/lib-services-framework', async () => {
   const actual = (await vi.importActual('@powersync/lib-services-framework')) as any;
@@ -25,7 +25,7 @@ describe('Probe Routes Integration', () => {
 
   beforeEach(async () => {
     app = Fastify();
-    mockSystem = { routerEngine: {} } as system.ServiceContext;
+    mockSystem = { routerEngine: {}, replicationEngine: {} } as system.ServiceContext;
     await configureFastifyServer(app, { service_context: mockSystem });
     await app.ready();
   });

packages/service-core/test/src/routes/probes.test.ts

@@ -1,6 +1,6 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { container } from '@powersync/lib-services-framework';
-import { startupCheck, livenessCheck, readinessCheck } from '../../../src/routes/endpoints/probes.js';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { livenessCheck, readinessCheck, startupCheck } from '../../../src/routes/endpoints/probes.js';
 
 // Mock the container
 vi.mock('@powersync/lib-services-framework', () => ({
@@ -83,6 +83,7 @@ describe('Probe Routes', () => {
   });
 
   describe('livenessCheck', () => {
+    const mockedContext = { context: { service_context: { replicationEngine: {} } } } as any;
     it('has the correct route definitions', () => {
       expect(livenessCheck.path).toBe('/probes/liveness');
       expect(livenessCheck.method).toBe('GET');
@@ -97,7 +98,7 @@ describe('Probe Routes', () => {
 
       vi.mocked(container.probes.state).mockReturnValue(mockState);
 
-      const response = await livenessCheck.handler();
+      const response = await livenessCheck.handler(mockedContext);
 
       expect(response.status).toBe(200);
       expect(response.data).toEqual(mockState);
@@ -112,7 +113,7 @@ describe('Probe Routes', () => {
 
       vi.mocked(container.probes.state).mockReturnValue(mockState);
 
-      const response = await livenessCheck.handler();
+      const response = await livenessCheck.handler(mockedContext);
 
       expect(response.status).toBe(400);
       expect(response.data).toEqual(mockState);