Databases on AWS

Databases on AWS

• RDS ( MySQL, PostgreSQL, SQL Server, MariaDB, Aurora)
• DynamoDB - Non relational DB (important for developer exam)
• Redshift  - Data warehousing system - 
• ElastiCache - Cloud in-memory DB (important for developer / architect exam)

RDBMS

RDBMS Types

• MS-SQL Server
• Oracle
• MySQL
• PostgreSQL
• Aurora
• MariaDB

NoSQL DBs

Document Oriented

• CouchDB
• MongoDB
• Dynamo DB

Collection = Table, Document = Row, Keys-Value Pairs = Fields

Data Warehousing

OLTP (pulls out specific / narrow record set) vs OLAP – (pulls in large number of records). It used different architecture and infrastructure layer. Differ in terms of queries run on top of data. OLAP is more about aggregation.

ElastiCache

In memory cache in cloud.

• Memcached
• Redis

Exam – Improve database performance – e.g. top 10 deals of the day.

Database Migration Service

Migrate production database to AWS. AWS manages all complexities of migration process. Source database remains fully operational. Both homogenous (Oracle to Oracle) as well as heterogeneous migrations are supported (Oracle to Aurora or Microsoft SQL). Can also be used for continuous data replication with high availability

AWS Schema migration tool makes heterogeneous database - migrations - easy by automatically converting the source database schema and a majority of the custom code, including views, stored procedures, and functions, to a format compatible with the target database. Any code that cannot be automatically converted is clearly marked so that it can be manually converted.

RDS – Back Ups, Multi AZs & Read Replicas

OLTP systems.

Backups

• Automated Backups – full daily snapshot & will also store transaction logs.
• Enabled by default. Stored in S3. Free backup storage in S3 upto the RDS Instance size.
• You can define backup window. Choose wisely.
• Backups are deleted when the RDS Instance is deleted.

Snapshots

• Done manually. They are stored even after you delete the instance.
• You can copy snapshots across regions.
• You can publish the snapshot to make it publically available.
• Restoring Backups/ Snapshots – The restored version will be a new RDS instance with new end point.
• You can check the instance size to restore.
• You cannot restore to existing instance

Encryption

• Encryption at rest is supported for MySQL, SQL Server, Oracle and PostgreSQL & MariaDB.
• Managed by AWS KMS.
• Cannot encrypt an already present instance. To encrypt, create new instance with encryption enabled and then migrate your data to it.

Multi-AZ Deployment

• A standby copy is created in another AZ. AWS handles replication and auto-failover
• AWS can automatically failover RDS instance to another instance.
• In case of failover, No need to change connection string.
• This can be used for DR purpose only. This option has to be selected at instance creation time. This option is not useful for improving performance / scaling.

Read Replica Databases.

• Read-replica – async data transfer to another RDS instance. You can actually read from these instances, unlike Multi-AZ deployments. You can also have read replicas of read-replicas up to 5 copies. (Watch out as async causes latency)-
• Read-replicas can be used for Dev/Test environments, run certain workloads only against them and not against direct production deployment – Intensive workloads.
• MySQL , MariaDB, PostgreSQL only for read-replicas , no Oracle & SQL Server
• You cannot have read-replicas that have multi-AZ. However, you can create read replicas of Multi AZ source databases.
• Read replicas can be of a different size than source DB.
• Each read-replica will have its own DNS end point
• Automatic backups must be turned on in order to deploy a read replica
• Read Replicas can be promoted to be their own databases. This breaks replication. E.g. Dev/Test can be connected to the replica by first promoting it as DB itself.
• Read Replicas can be done in a second region for MySQL and MariaDB – no PostgreSQL.
• Application re-architecture is required to make use of Read replicas
• Read replicas are not used for DR. they are used for performance scaling only.

DynamoDB

• Fast and flexible NoSQL database
• Consistent, single digit millisecond latency.
• Fully managed DB – supports both document based & Key-value data models.
• Great fit for mobile, IoT, web, gaming etc. applications.
• Stored on SSDs
• Stored on 3 geographically distinct DCs (not AZs). Built in redundancy
• Consistency

1. Eventual consistent reads - Consistency reached up to 1 second (default)
2. Strongly Consistent reads - Consistency reached after writes to all copies are completed. <1 second

Select type based on application needs

• Pricing – Write Capacity Units and Read Capacity Units ($/hr.). Also Storage cost per month. You provision capacity in units/second. It can scale on the fly. Provisioned capacity.
• Dynamo DB – Expensive for Writes. Cheap for Reads. Important point v/s RDS.
• You can dynamically add columns – without the need to update other rows with the column data. As this is no RDBMS.
• Reserved capacity is available for DynamoDB as well.

RDS v/s DynamoDB

• Use DynamoDB for Push button scaling. With RDS – to scale horizontally a new instance has to be created.
• DynamoDB is cheap for writes and expensive for reads.
• Observe workload characteristics and decide
• Use RDS if data requires joins and relationships.
• In RDBMS database structure cannot be dynamically altered. With DynamoDB you can.

Redshift

Petabyte scale DW solution in cloud. Used for OLAP – sum of various columns and joining the data.

Configurations

• Single Node – 160 GB. Used by Small and Medium Size businesses.
• Multi-Node – Leader Node (handles all incoming connections & receives queries) & compute Node (store data and perform queries and computations – up to 128 Compute Nodes)

Performance

• Redshift is 10 times faster than usual OLAP systems.
• It uses Columnar Data Store. Columnar data is stored sequentially on storage system. Hence low I/O required – improving performance.
• Advanced Compression (easier to do it via Columns instead of via Rows – which have different data types). Columns have similar type of data. Doesn’t use indexes and views – hence less storage required.
• Based on data, appropriate data compression scheme is used.
• Allows for massive parallel processing

Pricing

• Based on Compute Node hours (compute node only – no leader node).
• Backup and Data Transfer (only within VPC)

Security

• Transit encrypted via SSL,
• At rest using AES-256 encryption
• Can use your own HSM or default AWSK Key management.

Availability

Not Multi-AZs. Can restore snapshots

Exam Tips – Database warehousing service, cheap, faster. Best seller AWS Service. Speed achieved due to columnar storage. And Data stored sequentially on disk – hence faster.

ElastiCache

• Easy to deploy, operate and scale an in-memory cache in the cloud.
• Improve performance by avoiding repeated calls to DB.
• Improve latency and throughput for read-heavy applications.
• Can be used for compute intensive data

Memcached

• All Memcached tooling can be easily ported over.

Redis

• Supports Master / Slave replication and multi-AZ deployment to get redundancy.

Exam Tips

• ElastiCache is used if DB is primarily read-heavy and not frequently changing
• Use Redshift – if application is slow due to constant OLAP transactions on top of OLTP focused DB.

Aurora

• Bespoke Database Engine.
• It is MySQL compatible.
• However you can’t download and install on your workstation.

Performance

5 times better performance than MySQL. At a fraction of cost as compared to Oracle.

Scaling

• Outset 10 Gb Storage, auto increment of storage
• No Push button scaling – unlike DynamoDB

Fault Tolerance

• Maintains 2 copies of your data in at least 3 availability zones. This is for the Data only not for the instances that runs the Database.
• 2 copies lost – no impact on write availability.
• 3 copies lost – no impact on read availability.
• Storage is self-healing.

Replicas

• MySQL Read Replica can be created from the Aurora source DB.(up to 5 of them)
• Aurora Replicas – up to 15 of them. If leader crashes, the replica with the highest tiers becomes the leader. While creating replicas, remember to assign different tier levels.
• Cluster Endpoint vs Individual Endpoint

No Free Tier usage available. Also available only in select regions. Takes slightly longer to provision

Exam Tips

• Why you can’t connect to DB Server from DMZ. Check the security group – if it is removed or added
• Have separate groups for EC2 Instance and RDS Instance.
• Multi-AZ for Disaster Recovery only. Not for performance improvement. For performance improvement use, multiple read-replicas
• Dynamo DB v/s RDS

If you want push button scaling, without any downtown, you will always want to use DynamoDB.

With RDS scaling is not so easy, you have to use a bigger instance or add read replicas (manual process).

• If you are using Amazon RDS Provisioned IOPS storage with a MySQL or Oracle database engine, what is the maximum size RDS volume you can have by default? – 6TB
• What data transfer charge is incurred when replicating data from your primary RDS instance to your secondary RDS instance? - There is no charge associated with this action.
• When you have deployed an RDS database into multiple availability zones, can you use the secondary database as an independent read node? – No
• RDS automatically creates RDS Security Group w/ TCP port # 3306 enabled. 
• In VPC Security Group, the answer would be YES because you will have manually specify access to port & protocol.

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• AWS Cloud #Databases provides a broad selection of purpose-built databases for any enterprise.
•  AWS databases support all database management tasks, such as server provisioning, patching, configuration, and backups.
•  AWS provides various databases to supports relational and non-relational databased requirements to the clients.

Types of Database Services:

• Relational Database
• Key–Value Database
• In Memory Database

Relational Database

In relational database data is stored in a tabular format. It uses SQL to run queries to perform operations such as insertion, updating, deletion, and more. AWS provides following relational database services.

•  Amazon RDS

Amazon Relational Database Service is a collection of managed services that makes it simple to set up, operate, and scale databases in the cloud.

It provides six database engines to choose and that includes Amazon Aurora, PostgreSQL, MySQL, MariaDB, Oracle Database, and SQL Server.

•  Amazon Redshift

Amazon Redshift uses SQL to analyze structured and semi-structured data across data warehouses, operational databases, and data lakes, using AWS-designed hardware and machine learning to deliver the best price performance at any scale.

•  Amazon Aurora

Amazon Aurora provides built-in security, continuous backups, serverless compute, up to 15 read replicas, automated multi-Region replication, and integrations with other AWS services.

 Key Value Database

 key-value database is a type of non-relational database that uses a simple key-value method to store data. A key-value database stores data as a collection of key-value pairs in which a key serves as a unique identifier.

•  Amazon DynamoDB

Amazon DynamoDB is a fully managed, serverless, key-value NoSQL database designed to run high-performance applications at any scale.

DynamoDB offers built-in security, continuous backups, automated multi-Region replication, in-memory caching, and data import and export tools.

 In Memory Database

In-memory databases are purpose-built databases that rely primarily on memory for data storage, in contrast to databases that store data on disk or SSDs.

•  Amazon ElastiCache

Amazon ElastiCache is a fully managed, in-memory caching service supporting flexible, real-time use cases.

It accelerates application and database performance, or as a primary data store for like session stores, gaming, streaming, and analytics.