AWS, BIG DATA, JAVA

Amazon Aurora allows creating up 15 read replicas in a region. Read replicas share the source storage. Storage scales automatically into 10GB increments up to 64 TB. There is option for Global Database which allows single database to span across multiple regions.  It uses storage based replication. By default Aurora database is replicated six ways across three AZs. It can handle loss of two copies without affecting writes and three copies without affecting reads. Aurora also has a backtrack feature, it can go back to point in time without restore from a backup. 

For every domain which you want to manage, you need to create a hosted zone. Within Hosted zone , you can configure various record sets which specify how traffic within that domain will be routed. There are various types of records.  Typically A record points to an IP address or is an alias to another endpoint or record within same hosted zone.    CNAME record is slightly different. CNAME can point to another  domain or sub-domain ( not IP address ) . You can not create  CNAME for zone -apex (or  hosted zone itself).  A CNAME record can redirect DNS queries to any DNS record. A few important differences between CNAME and aliases are listed on below link. https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/resource-record-sets-choosing-alias-non-alias.html

1. How to get the list of all the tables , views and stored procedures etc from a  Teradata database. select TableKind , TableName from DBC.TABLES where DatabaseName='db_name' TableKind  can be T, O, Q, P, V ....

HTTP/2.0 modifies  how data is formatted and transported between client and server, in doing so , it encapsulates all this  additional complexity in a new framing layer both on the client and server side.  So  applications built on previous versions of protocol continue to work except with added benefits of being faster and with some new capabilities at their disposal  like request prioritization , flow control and server push. 

It is two way ( full-duplex - in both direction at same time ) communication protocol between server & client using long running TCP connection.  Client  & server both  can send messages to one another in asynchronous manner.  The messages are sent with very little overhead and hence results in very low latency. Websockets remove the need for long polling in the HTTP based applications needing real time updates from server.  Long-polling is done so that client application does not have to keep polling/requesting  server for updates as it results in  frequent HTTP connection overheads.  So client makes a request and server waits as long as it can, until either there is update for client or it times out. This is called long polling.  How websockets work ? 

Kinesis Data Analytics can use standard SQL queries to process kinesis data streams and can ingest data from Kinesis Data Streams and kinesis Firehose.  Kinesis Firehose can be used for running SQL queries. ( Udemy ). DynamoDB has two pricing models; on-demand ( unpredictable traffic ) and provisioned (predictable). With API Gateway, you can maintain multiple versions and multiple stages of each version of an API. Access Policy vs. ACL IAM Policy vs. Password Policy You can not assign deny rules to a security group. ALB only features: - Path Based Routing - Host Based Routing - HTTP Method Based Routing - HTTP Header Based Routing -Query String Parameter Based Routing -Source IP Address-CIDR Based Routing -Native HTTP/2  NLB  only features: -Static IP -Elastic IP -Source IP Preservation ( at some places it talks that all ALB , GLB also support this )  CLB only features -Custom security policies SNI , secure listener Amazon Cognito lets ...

Here are few differences mentioned on one of  Udemy Practice Test: Redis stores data persistently but not memcached.  Redis supports multi-AZ with read replicas in another AZ in same region. You can have a fully automated, fault tolerant ElastiCache-Redis implementation by enabling both cluster mode and multi-AZ failover Memcached engine does not support Multi-AZ failover or replication. References: https://digitalcloud.training/certification-training/aws-solutions-architect-associate/database/amazon-elasticache/