RxJS: important link for rxjs.

1. https://blog.kwintenp.com/how-share()-can-reduce-network-requests/
2. https://coryrylan.com/blog/angular-multiple-http-requests-with-rxjs
3. https://www.learnrxjs.io/operators/multicasting/share.html
4. https://coryrylan.com/blog/angular-multiple-http-requests-with-rxjs
5. http://plnkr.co/edit/L2eHKy2mZg4oTwxL6PMy?p=preview (important)
6. https://www.learnrxjs.io/operators/combination/combineall.html (tutorial)
7.  

Amazon RDS:

Amazon Relational Database Service (Amazon RDS) is a web service that makes it easier to set up, operate, and scale a relational database in the cloud. It provides cost-efficient, resizable capacity for an industry-standard relational database and manages common database administration tasks.

Amazon Aurora

Amazon Aurora (Aurora) is a fully managed, MySQL-compatible, relational database engine that combines the speed and reliability of high-end commercial databases with the simplicity and cost-effectiveness of open-source databases. It delivers up to five times the performance of MySQL without requiring changes to most of your existing applications.

Amazon Aurora is a drop-in replacement for MySQL. The code, tools and applications you use today with your existing MySQL databases can be used with Amazon Aurora.

When you create an Amazon Aurora instance, you create a DB cluster. A DB cluster consists of one or more instances, and a cluster volume that manages the data for those instances. An Aurora cluster volume is a virtual database storage volume that spans multiple Availability Zones, with each Availability Zone having a copy of the cluster data. Two types of instances make up an Aurora DB cluster:

• Primary instance: Supports read-write workloads, and performs all of the data modifications to the cluster volume. Each Aurora DB cluster has one primary instance.
• Aurora Replica: Supports only read operations. Each DB cluster can have up to 15 Aurora Replicas in addition to the primary instance, which supports both read and write workloads. Multiple Aurora Replicas distribute the read workload, and by locating Aurora Replicas in separate Availability Zones you can also increase database availability.

The following diagram illustrates the relationship between the Amazon Aurora cluster volume and the primary and Aurora Replicas in the Aurora DB cluster.

Merits:

1. It delivers up to five times the throughput of standard MySQL running on the same hardware.
2. Amazon Aurora joins MySQL, Oracle, Microsoft SQL Server, and PostgreSQL as the fifth database engine available to customers through Amazon RDS. Amazon RDS handles time-consuming tasks such as provisioning, patching, backup, recovery, failure detection, and repair.
3. You pay a simple monthly charge for each Amazon Aurora database instance you use. There are no upfront costs or long-term commitments.
4. Amazon Aurora's storage is fault-tolerant and self-healing.
5. Disk failures are repaired in the background without loss of database availability.
6. Amazon Aurora scales storage automatically, growing storage and rebalancing I/Os to provide consistent performance without the need for over-provisioning. For example, you can start with a database of 10GB and have it automatically grow up to 64TB without requiring availability disruptions to resize or restripe data.
7. Amazon Aurora is a drop-in replacement for MySQL. The code, tools and applications you use today with your existing MySQL databases can be used with Amazon Aurora .

Aurora Endpoints:

An endpoint is made up of a domain name and a port separated by a colon, for example: mydbcluster.cluster-123456789012.us-east-1.rds.amazonaws.com:3306. Choose the best endpoint for your scenario from the following.

• Cluster endpoint : Each Aurora DB cluster has a cluster endpoint that you can connect to. The cluster endpoint connects you to the primary instance for the DB cluster. You can perform both read and write operations using the cluster endpoint.

The primary instance also has its own unique endpoint. The difference between these two endpoints is that the cluster endpoint will always point to the current primary instance. In other words, if the primary instance fails, then the cluster endpoint will point to the new primary instance. If the primary instance fails, you will need to re-establish your connection.

• Reader endpoint: Each Aurora DB cluster has a reader endpoint that you can use to connect to one of the Aurora Replicas in your DB cluster. The reader endpoint for a DB cluster load-balances connections across the Aurora Replicas that are available in a DB cluster.
• Instance endpoint: The primary instance and Aurora Replicas in a DB cluster all have an instance endpoint, which is a unique endpoint that you can use to connect directly to the specific instance. Instance endpoints don't include cluster- in the identifier. For example, the cluster endpoint might be mydbcluster.cluster-123456789012.us-east-1.rds.amazonaws.com:3306, and the instance endpoint for the primary instance might be mydbcluster-primary.123456789012.us-east-1.rds.amazonaws.com:3306.

Amazon Aurora Storage:

Aurora data is stored in the cluster volume, which is a single, virtual volume that utilizes solid state disk (SSD) drives. A cluster volume consists of copies of the data across multiple Availability Zones in a single region. Because the data is automatically replicated across Availability Zones, your data is highly durable with less possibility of data loss. This replication also ensures that your database is more available during a failover because the data copies already exist in the other Availability Zones and continue to serve data requests to the instances in your DB cluster.

Aurora cluster volumes automatically grow as the amount of data in your database increases. An Aurora cluster volume can grow to a maximum size of 64 terabytes (TB). Table size is limited to the size of the cluster volume. That is, the maximum table size for a table in an Aurora DB cluster is 64 TB. Even though an Aurora cluster volume can grow to up to 64 TB, you are only charged for the space that you use in an Aurora cluster volume.

Comparison of Amazon Aurora and Amazon RDS for MySQL :

• Amazon RDS for MySQL:
  

1. Supports up to 5 Read Replicas
2. Read Replicas can be manually promoted to the master DB instance with potential data loss
3. Supports MySQL versions 5.5, 5.6, and 5.7.
4. Available in all AWS regions.
5. Supports both MyISAM and InnoDB.

• Amazon Aurora:
  

1. Supports up to 15 Aurora Replicas
2. Aurora Replicas are automatic failover targets with no data loss.
3. Supports only MySQL version 5.6.
4. Aurora DB clusters can only be created in the some specific regions
5. Supports only InnoDB.

Ref:

• https://aws.amazon.com/rds/aurora/details/
• http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Welcome.html
• http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Overview.html