feat: added read replica option in config and extended knex to choose

backend/src/db/instance.ts

@@ -1,8 +1,34 @@
-import knex from "knex";
+import knex, { Knex } from "knex";
 
 export type TDbClient = ReturnType<typeof initDbConnection>;
-export const initDbConnection = ({ dbConnectionUri, dbRootCert }: { dbConnectionUri: string; dbRootCert?: string }) => {
-  const db = knex({
+export const initDbConnection = ({
+  dbConnectionUri,
+  dbRootCert,
+  readReplicas = []
+}: {
+  dbConnectionUri: string;
+  dbRootCert?: string;
+  readReplicas?: {
+    dbConnectionUri: string;
+    dbRootCert?: string;
+  }[];
+}) => {
+  let db: Knex;
+  let readReplicaDbs: Knex[];
+  // @ts-expect-error the querybuilder type is expected but our intension is to return  a knex instance
+  knex.QueryBuilder.extend("primaryNode", () => {
+    return db;
+  });
+
+  // @ts-expect-error the querybuilder type is expected but our intension is to return  a knex instance
+  knex.QueryBuilder.extend("replicaNode", () => {
+    if (!readReplicaDbs.length) return db;
+
+    const selectedReplica = readReplicaDbs[Math.floor(Math.random() * readReplicaDbs.length)];
+    return selectedReplica;
+  });
+
+  db = knex({
     client: "pg",
     connection: {
       connectionString: dbConnectionUri,
@@ -22,5 +48,21 @@ export const initDbConnection = ({ dbConnectionUri, dbRootCert }: { dbConnection
     }
   });
 
+  readReplicaDbs = readReplicas.map((el) => {
+    const replicaDbCertificate = el.dbRootCert || dbRootCert;
+    return knex({
+      client: "pg",
+      connection: {
+        connectionString: el.dbConnectionUri,
+        ssl: replicaDbCertificate
+          ? {
+              rejectUnauthorized: true,
+              ca: Buffer.from(replicaDbCertificate, "base64").toString("ascii")
+            }
+          : false
+      }
+    });
+  });
+
   return db;
 };