Database Flashcards
What are the DB Instance Types?
M (Multipurpose)
R (RAM / Memory)
T (Tiny / Burstable)
What are the Aurora features for automatic reliability?
Storage Auto Repair (detects failing discs)
“Survivable” cache warming (separate process to warm cache)
Crash Recovery (almost instant recovery
What are the three security levels for Aurora?
IAM
Security Groups
Database Authentification
What are the three storage types?
Magnetic, General Purpose & Prov. IOPS
When does RDS automatically fail over?
Loss of AZ
Loss of network connectivity to primary instance
Compute unit failure on primary instance
Storage failure on primary instance
How to enable Multi-AZ on RDS?
It can be created new or as a modification
What to consider for read replicas?
- Automated backup must be enabled
- Cannot be used behind an ELB
- Can be promoted to primary, will break the replication
- Up to 5 RRs (mysql/postgres)
- Up to 15 RRs for Aurora
- Multi Region for mysql, postgres & aurora
- Database snapshots cannot be made from RRs
How is the failover process for RDS structured?
Automatically, needs 60-120s (more for large DBs)
It changes the DNS endpoint
What is RDS Snapshot Copy?
Possibility to copy snapshots to any public Region
How are automatic snapshots generated?
Daily in the backup window. I/O can be reduced in that time.
It cannot overlap with the weekly maintenance window.
How to scale up in a Multi-AZ environment?
First the Standby will be upgraded, then there’s a minimal downtime when the primary is scaled
What is Sharding?
Horizontal partitions
Seperate instances that contain a subset of the whole dataset
What can be be monitored in RDS?
CPU/RAM/Disk space consumptions
Network traffic
Database connections
IOPS metrics
Dynamo DB: What is an item?
Group of attributes that can be uniquely identified from all other items
Dynamo DB: How are RCU calculated?
One read capacity: 1 strongly consistent read or 2 eventually consistent read of 4KB
Dynamo DB: How are WCU calculated?
1KB in size = 1 WCU
Dynamo DB: What is Reserved Capacity?
Reserving RCU/WCU for a fee, which reduces the cost of the IOPS
DynamoDB: How do indicies affect WCU?
Every WCU scales with the amount of indices.
1 primary: 1KB
1 primary + index: 2KB
DynamoDB: What happens when the prov. throughput is exceeded?
It fails with a 400 code.
AWS SDK have an automatic retry.
What is the benefit of a VPC endpoint?
- no need for internet of NAT
- no need for additional firewalls
- no additional costs
Redshift: What is the purpose of the leader node?
It receives the queries, parses them and develops execution plan
What is the maximum number of data copies that Amazon Aurora can lose without affecting writes?
Amazon Aurora at maximum can withstand the loss of two copies of data without affecting writes
What CloudWatch metric is used to determine needs for storage type changes?
ReadIOPS/WriteIOPS is a metric used to determine a need for storage type changes.
What are two of the available node types for Amazon ElastiCache of the current generation?
Memory Optimized & General Purpose
What needs to be done when a RDS failover occurs.
Nothing, the connection endpoint will stay the same.
What is Replication Lag?
The time it takes for the RR to include the most current data
What is the requirement for enabling Read Replicas?
Enable automated backups
Can you create an read replica of a read replica?
Yes, but here also automated backups need to be enabled for the original RR as well
How to use an existing database for testing?
Promote a read replica as master - therefore you now have two databases in parallel
How to encrypt an existing database?
Take a snapshot
Copy the snapshot in the same or different region with encryption enabled
Create a database
How to share an encrypted RDS Snapshot with another account?
- Create a custom (not the default) KMS Key and share it with the other account
- Encrypt the database with that key
Which ElastiCache engine supports Multi-AZ?
Redis
RDS: How to scale?
Increase the size. (Scaling up)
It is not possible to scale out RDS
RDS: What are the benefits of Multi-AZ?
- High availability (failover)
- Backups are taken from the standby
- Restores are taken from the standby
RDS: What happens when a Read Replica is created?
AWS takes a snapshot of the data (from the primary, o r the secondary if Multi AZ is enabled)
RDS: What are the restriction to share an encrypted RDS Snapshot?
- Cannot be encrypted with the default KMS Key
- ## Cannot be shared public
RDS: What is Aurora Serverless?
Automatically scaling database, where you are paid by the second of usage.
Very like Lambda.
Which CLI command can you use to determine which version of RDS you are using?
describe-db-instances
DynamoDB: How to use scheduled provisioning?
It is not possible to scale on a schedule, use auto-scaling instead
You need to check the OS of the instances to ensure that the latest patches are installed and that the proper security requirements are being met. What AWS service could you use to complete your task?
Check maintenance of the instances on the Amazon RDS console.
RDS: What are the two methods of backups?
point-in-time-recovery: database and transaction backup - allows to jump to a certain point in time.
Is stored for 35 days
DB Snapshots: Full database backup. Can be moved to another region and also used to create a new database
RDS: How to avoid I/O suspension on backups
Use Multi-AZ
Redshift: What happens, when a drive fails?
It is automatically replaced
Redshift: What is an Audit Log?
Stores all SQL operations, such as login attempts, queries or changes to the database
Which service can be used to migrate a database?
AWS Database Migration Service
How does DynamoDB provide HA and high performance?
HA: It automatically replicates data to multiple AZs in a region.
Performance: It generates more partitions and provisions more server capacity if the table grows or mote throughput is needed
What affects I/O?
Snapshot creation
Backups
Read Replica creation
Scaling storage
RDS: Is it possible to create a Multi-.AZ setup after database creation?
yes
RDS: What is RDS Snapshot Copy?
Possibility to copy snapshots to different regions.
Is a copy already exists only the storage delta is transferred
What is a DynamoDB Stream?
Metadata about every create, update or delete on the table
DynamoDB: What function is called for a single item or multiple items?
single: GetItem
multiple: BatchGetItem
What would you call databases in a NoSQL implementation?
In a NoSQL implementation, databases are referred to as stores, and there are four
types of stores: document, graph, key/value, and wide column.
Which type of NoSQL store is optimized for querying really large datasets?
Wide column stores
What is the (soft) limit for RDS database?
40
When would it be okay to disable automated backups?
When you are loading a large amount of data.
RDS: When must the decision to encrypt a database be made? on creation or any time?
on creation.
RDS: . What would be the best solution to
enable messages related to changes with your RDS clusters?
Amazon RDS events
Which on is asynchronous, which one is synchronous?
Read-Replica, Multi AZ
Read-Replica: asynchronous
Multi AZ: synchronous
