Added Portal database backup documentation

docs/PORTAL_BACKUP.md

@@ -0,0 +1,28 @@
+# Portal Backup
+
+## Database
+
+> How is the Portal backend database backed up?
+
+Portal database has 2 tiers backup setup.
+
+### Tier 1
+- Short-term; fine-grain database backup using [RDS automated backup](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ManagingAutomatedBackups.html) service.
+- 7 days point-in-time (PIT) retention.
+
+### Tier 2
+- Longer-term; RDS database instance backup using [AWS Backup](https://docs.aws.amazon.com/prescriptive-guidance/latest/backup-recovery/aws-backup.html) service.
+- Backup weekly snapshot and keeping it for 6 weeks retention.
+
+### Recovery Point Objective
+
+By a combination of 2 tier backup setup, we can effectively restore database to any _point-in-time_ within past 7 days. After day 7, we can restore the database to its weekly state; upto past 6 weeks. (See [RPO](https://www.google.com/search?q=recovery+point+objective)). By leveraging multiple backup services, it systematically increases backup redundancy.
+
+### Encryption
+
+- RDS automated backups are encrypted and, database instance is deletion protected.
+- AWS Backup Vault is encrypted with KMS.
+
+### Operation
+
+- Database maintenance and restore operations (DBA tasks) are carried out by trained person. (See [PORTAL_RELEASE.md](PORTAL_RELEASE.md))