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---
title: 15 - RDS
course: ["aws solutions architect"]
---
# Relational Database Services (RDS)
- RDS is a managed database service from AWS
- It uses SQL and supports the following databases:
1. Postgres
2. MySQL
3. MariaDB
4. Oracle
5. Microsoft SQL server
6. IBM DB2
7. Aurora (AWS proprietary service)
## Why use a managed service?
AWS manages the whole service for you, including deployment of databases onto infrastructure. Because it's managed, you don't have access to the underlying infra, so you can't SSH into the DB servers.
Advantages of this:
- Automated provisioning, OS patches
- Backups
- Monitoring dashboards
- Scaling (horizontal and vertical)
- Multi AZ (recovery)
- Read replicas (performance)
## Storage Auto Scaling
AWS can scale DB stores automatically depending on usage. For e.g when you are running out of DB space.
You have to set a **Maximum Storage Threshold**.
> Auto scaling is good for apps with unpredictable DB operations## Storage Auto Scaling
## Read Replicas VS Multi AZ
### Read Replicas
Read replicas are DB replicas of the main DB that allow for more read operations (scalability).
They work by replicating the main DB and then allowing read operations to those replicas.
The data between the main DB and replica DBs is _eventually consistent_, meaning that they will eventually have identical data, but there is a chance a read operation to a replica will receive back outdated data.
Replicas can also be promoted to their own DB.
#### Network Costs for replicas
There are network costs associated with replicas. If you replicate across a different AZ, a fee is incurred, else it's free.
### Multi AZ
Multi AZ RDS are DB instances that are on standby should something go wrong with the master DB.
This helps increase availability
> Multi AZ RDS is good for database availability
There is just one DNS name needed and if there is network loss, instance of storage failure, read and write operations will be passed to the instance on standby:
**There is no downtime associated when creating Multi AZ - you just modify the DB**
> Important to know that you can also use read replicas for Disaster Recovery (DS)
## RDS Custom
While it's been mentioned that RDS is a fully managed service, with two databases you do get OS access and can SSH into the instances:
- Orcale
- Microsoft SQL server
For these two DBs you can:
- Configure settings
- Install patchesEnable features
- Access EC2 instance using SSH
> RDS is a managed services, except for Oracle and MS SQL, which allow customisation and EC2 access
## Amazon Aurora
This is Amazon's proprietary database offering, it's not open source. It:
- Aurora works with bothPostgres and MySql.
- Has 5x better perf than MySQL and 3x the perf of Postgres
- Storage automatically grows in 10GB increments, up to 128TB
- Can have 15 read replicas
- Failover is instantaneous
### Aurora availability and read scaling
Aurora created 6 copies of data across 3 AZs (diagram).
The storage is self healing and auto expanding.
One instance takes writes (the master) and the data is replicated across the instances, which can be used for read operations.
## Aurora Cluster
Aurora has a:
1. Shared volume
2. 1 master writer - one endpoint
3. 5 readers - one endpoint that scale automatically
## Advanced - Aurora replicas and auto scaling
If read endpoints receive much more traffic then the read replicas will autoscale:
## Avanced - replicas and custom endpoints
By default, replicas share the same endpoint, but you can specify a custom endpoint should some of your replicas be unique, for example the DBs are larger or more powerful:
## Advanced - Aurora serverless
Serverless option from AWS that:
- automatically scales depending on usage
- no storage planning needed
- pay per second pricing model
## Advanced - global availability
For global availability you can:
1. Create Aurora cross region availability using read replicas
2. Use an Aurora global database (recommended):
The global database has:
- 1 primary region
- up to 5 additional read only regions
- 16 read replicas in the regions
- helps decrease latency globally
- replication takes less than 1s
> In the exam when "cross region replication < 1s" is mentioned, it's referring to Aurora Global
## Advanced - Aurora Machine Learning
SQL integration with other AWS ML tools: SageMaker and Comprehend. It basically takes data from your Aurora tables and uses them to power ML tools. The data will be routed through Aurora:
## RDS Backups
There are two ways to backup:
1. Automated Backups: daily full backups, can restore from any point up to 5 min before backup (so any time in the past up until 5min ago). 1-35 days retention
2. Manual DB Snapshots: manually triggered and retention as long as you want
> To save money, instead of stopping a DB (you will still pay) you can create a snapshot and restore from there in the future
## Aurora backups
It's similar, with automated backups and manual DB snapshots. Automated backups cannot be turned off!
## Restoring operations
Two options:
1. Restoring automatically from backup/snapshot. This will create a new DB.
2. Restore MYSQL / Aurora from S3. Involves creating a backup on S3 and then restoring from there. For Aurora you have to use Percona XtraBackup for this.
## Aurora DB cloning
Creates new Aurora cluster from an existing one. You can do this to run DB testing, for example.
When the new cluster is created and new write operations are made to it, new storage is allocated only to the new DB cluster.
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