feat(mongoose): force secondaryPreferred if no secondaries in cluster

- Trigger early load of mongoose before any other import and implicit
  load of mongoose model
- Add a global schema plugin that inspects schema for read preference
  - if `secondary`, check the cluster using mongoose connection
  - if cluster without secondaries, force read pref to be
    `secondaryPreferred`

replacements/src/app/loaders/mongoose.ts

@@ -4,6 +4,38 @@ import mongoose, { Connection } from 'mongoose'
 import config from '../config/config'
 import { createLoggerWithLabel } from '../config/logger'
 
+// Invoke this at module load time
+mongoose.plugin((schema) => {
+  if (schema.get('read') === 'secondary') {
+    // Inspect cluster topology from client
+    const client = mongoose.connection.getClient()
+    const {
+      description: { servers, type },
+      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+      // @ts-ignore
+    } = client.topology
+
+    if (
+      type === 'ReplicaSetWithPrimary' &&
+      !servers
+        .values()
+        .some(({ type }: { type: string }) => type === 'RSSecondary')
+    ) {
+      // There are no secondary nodes in ReplicaSetWithPrimary cluster.
+      // Queries with `secondary` read preferences will fail, so rewrite
+      // those to be `secondaryPreferred`.
+      logger.warn({
+        message: 'Forcing secondary read preference to secondaryPreferred.',
+        meta: {
+          action: 'schema',
+        },
+      })
+
+      schema.set('read', 'secondaryPreferred')
+    }
+  }
+})
+
 const logger = createLoggerWithLabel(module)
 
 export default async (): Promise<Connection> => {
@@ -90,30 +122,6 @@ export default async (): Promise<Connection> => {
     })
   })
 
-  // Seed db with initial agency if we have none
-  if (
-    process.env.INIT_AGENCY_DOMAIN &&
-    process.env.INIT_AGENCY_SHORTNAME &&
-    process.env.INIT_AGENCY_FULLNAME
-  ) {
-    const Agency = mongoose.model('Agency')
-    const agencyCount = await Agency.count()
-    if (agencyCount === 0) {
-      await mongoose.connection.collection(Agency.collection.name).updateOne(
-        { shortName: process.env.INIT_AGENCY_SHORTNAME },
-        {
-          $setOnInsert: {
-            shortName: process.env.INIT_AGENCY_SHORTNAME,
-            fullName: process.env.INIT_AGENCY_FULLNAME,
-            emailDomain: [process.env.INIT_AGENCY_DOMAIN],
-            logo: '/logo192.png',
-          },
-        },
-        { upsert: true },
-      )
-    }
-  }
-
   // Seed the db with govtech agency if using the mocked db
   if (usingMockedDb) {
     const Agency = mongoose.model('Agency')

replacements/src/app/server.ts

@@ -0,0 +1,27 @@
+import './loaders/datadog-tracer'
+import './loaders/mongoose'
+
+import config from './config/config'
+import { createLoggerWithLabel } from './config/logger'
+import loadApp from './loaders'
+
+const logger = createLoggerWithLabel(module)
+
+const initServer = async () => {
+  const app = await loadApp()
+
+  // Configure aws-sdk based on environment
+  // sdk is later used to upload images to S3
+  await config.configureAws()
+
+  app.listen(config.port)
+
+  logger.info({
+    message: `[${config.nodeEnv}] Connected to port ${config.port}`,
+    meta: {
+      action: 'initServer',
+    },
+  })
+}
+
+void initServer()