RDS

Amazon RDS Overview

• RDS : Relational Database Service
• is a managed service :
  • automated provisioning, OS patching
  • continuous backups and restore to specific timestamp
  • monitoring database
  • read replicas for improved read performance
  • multi AZ setup for Disaster Recovery
  • maintenance windows for upgrades
  • scaling capability (vertical and horizontal)
  • storage backed up by EBS
• but can't ssh into instances

RDS - Storage Auto Scaling

• helps to increase storge on RDS DB instance dyanamically
• when rds detects you are running out of free database storage, it scales automatically
• set maximum storage threshold
  • automatically modify storage if
    • free storage is less than 10% of allocated storage
    • low-storage lasts at least 5 mins
    • 6 hrs have passed since last modification
• useful for applications with unpredictable workloads

RDS Read Replicas for read scalability

• Up to 15 Read Replicas
• Within AZ, Cross AZ, or Cross Region
• Replication is ASYNC, so reads are eventually consistent
• Replicas can be promoted to their own DB
• Applications must update the connection string to leverage read replicas

• Read replicas are used for SELECT (= read) only kind of statements

RDS Read Replicas - Network Cost

• In AWS there's a network cost when data goes from one AZ to another
• For RDS Read Replicas within the same region, you don't pay that fee

RDS Multi AZ (Disaster Recovery)

• SYNC replication
• One DNS name - automatic app failover to standby
• Increase availability
• Failover in case of loss of AZ, loss of network, instance or stroage failure
• No manual intervention in apps
• Not used for scaling 

RDS - From Single-AZ to Multi-AZ

• Zero downtime operation ( no need to stop the DB )
• A snapshot is taken
• A new DB is restored from the snapshot in a new AZ
• Synchronization is established between the two databases 

RDS Custom

• Access to the underlying database and OS so you can
  • Configure settings
  • Install patches
  • Enable native features
  • Access the underlying EC2 Instance using SSH or SSM (AWS에서 인프라를 보고 제어하기 위해 사용할 수 있는 AWS 서비스)
  • De-active Automation Mode to perform customization, better to take a DB snapshot before

RDS Backups

• Automated backups :
  • Daily full backup of database
  • Transaction logs are backed-up by RDS every 5 mins
  • 1 to 35 days of retention, set 0 to disable automated backups
• Manual DB Snapshots
  • Manually triggered by the user
  • Retention of backup for as long as you want

Amazon Aurora

• proprietary technology from AWS
• Postgre and MySQL, supported as Aurora DB
• AWS cloud optimized, 5 x performance improvement over MySQL on RDS and 3 x performance improvement of Postgre on RDS
• automatically grows in increments of 10GB, up to 128 TB
• can have up to 15 replicas and the replication process is faster than MySQL
• Failover in Aurora is instantaneous, High Availability native
• costs more than RDS about 20%, but more efficient

Aurora High Availability and Read Scaling

• 6 copies of data cross 3 ZA
  • one aurora instance takes writes(master)
• automated failover for master in less than 30 seconds
• Master + up to 15 Aurora Read Replicas serve reads
• Support for Cross Region Replication

Features of Aurora

• Automatic fail-over
• Backup and Recovery
• Isolation and security
• Industry compliance
• Push-button scaling
• Automated Patching with Zero Downtime
• Advanced Monitoring
• Routine Maintenance
• Backtrack : restore data at any point of time without using backups

Aurora - Custom Endpoints

• define a subset of Aurora Instance as a custom endpoint
  • run analytical queries on specific replicas
• the reader endpoint is generally not used after defining Custom Endpoints

Aurora  Serverless

• Automated database instantiation and autoscaling based on actual usage
• Good fro infrequent, intermittent or unpredictable workloads
• No capacity planning needed
• Pay per second, can be more cost-effective'

Global Aurora

• Aurora Cross Region Read Replicas:
  • Useful for disaster recovery
  • Simple to put in place
• Aurora Global Database :
  • 1 Primary Region (read/write)
  • Up to 5 secondary (read-only) regions, replication lag is less than 1 second
  • Up to 16 Read Replicas per secondary region
  • Helps for decreasing latency
  • Promoting another region(for disaster recovery) has an RTO of < 1 min
  • Typical cross-region replication takes less than 1 second

Aurora Machine Learning

• Enables to add ML-based predictions to application via SQL
  • fraud detection, ads targeting, sentiment analysis, product recommendations

Aurora Backups

• Automated backups
  • 1 to 35 days
  • point-in-time recovery in that timeframe
• Manual DB snapshots
  • Manually triggered by the user
  • Retention of backup for as long as you want'

 

RDS & Aurora Restore options

• Restoring a RDS / Aurora backup or a snopshot creates a new database
• Restoring MySQL RDS database from S3
• Restoring MySQL Aurora cluster from S

Aurora Database Cloning

• create a new Aurora DB Cluster from an existing one
• faster than snapshot & restore
• uses copy-on-write protocol
• very fast & cost-effective
• useful to create a "staging" db from a "production" db without impacting the production db

RDS & Aurora Security

• At-rest encryption
• In-flight encryption
• IAM Authentication
• Security Groups
• No SSH available
• Audit Logs can be enabled

Amazon RDS Proxy

• Fully managed database proxy for RDS
• Allows apps to ppol and share DB connections established with the database
• Improving database efficiency by reducing the stress on database resource(CPU, RAM) and minimize open connections (and timeouts)
• Serverless, autoscaling, highly available (multi-AZ)
• Reduced RDS & Aurora failover time by up 66%
• Supports RDS and Aurora
• No code chages required for most app
• Enforce IAM Authentication for DB, and securely store credentials in AWS Secrets Manager
• RDS Proxy is never publicly accessible (MUST be accessed from VPC)

ElastiCache 

• to get managed Redis or Memcached
• helps reduce load off of databases for ead intensive workloads
• helps make your application stateless
• aws takes care of OS maintenance / patching, optimizations, setup, configuration, monitoring, failure recovery and backups
• using ElastiCache involves heavy application code changes

ElastiCache  Solution Architecture - DB Cache

• Applications queries ElastiCache, if not available, get from RDS and store in ElastiCache
• Helps relieve load in RDS
• Cache must have and invalidation strategy to make sure only the most current data is used in there 

ElastiCache  Solution Architecture - User Session Store

• User logs into any of the application
• The application writes the session data into ElastiCache
• The user hits another instance of our application
• The instance retrieves the data and the user is already logged in

ElastiCache  - Redis vs Memcached

• Redis
  • Multi AZ with Auto-Failover
  • Read Replicas to scale reads and have high availability
  • Data Durability using AOF persistence
  • Backup and restore features
  • Supprots Sets and Sorted Sets
• Memcached
  • Multi-node for partitioning of data
  • No high availability
  • Non persistent
  • No backup and restore
  • Multi-threaded architecture

ElastiCache  - Cache Security

• ElastiCache supports IAM Authentication for Redis
• IAM polices on ElastiCache are only used for AWS API-level security
• Redis AUTH
  • set pw/token when you create a Redis Cluster
  • an extral level of security for your cache
  • support SSL in flight encryption 
• Memcached
  • Supports SASL-based authentication(advanced)

Patterns for ElastiCache

• Lazy Loading
• Write Through
• Wession Store 

ElastiCache - Redis Use Case

• Gaming Leaderboards are computationally complex
• Redis Sorted sets guarantee both uniqueness and element ordering
• Each time a new element added, it's ranked in real time, then added in correct order