aws intro to dynamodb

DynamoDB is a NoSQL database that stores and retrieves data without having to define its structure/schema upfront. This is an alternative to relational databases that are rigid in structure.

General information

• Fast and flexible
  • Great for applications that need consistent, single-digit millisecond
  latency at any scale
• Fully managed
  • Supports key-value data models.
  • Supported document formats are JSON, HTML, XML
• Use cases
  • Great fit for mobile, web, gaming, IOT, and ad-tech.

Serverless

DynamoDB is a serverless database that can be configured to automatically scale. This is a popular choice for developers and architects that are already designing serverless applications.

Out of the box the DynamoDB offering integrates well with Lambda functions.

DynamoDB Features

• Performance - SSD storage
• Resilience - Data is spread across 3 geographically distinct data centers
• Consistency - Eventually consistent reads (default), strongly consistent reads, and ACID transactions

Consistency models

DynamoDB offers different data consistency models for different use cases.

Eventually consistent reads

Consistency across all copies of data is usually reached within a second.

If you read data that you changed 1 second ago, then the DB should return your recently changed data. This is best for read performance.

Strongly consistent reads

A strongly consistent read always reflects all successful writes. Writes are reflected across all 3 locations at once. This is best for read consistency.

ACID transactions

These are called DynamoDB Transactions and provide the ability to perform ACID transactions (Atomic, Consistent, Isolated, Durable). This enables the ability to read or write across multiple tables, in multiple transactions, in an all-or-nothing fashion.

Essentially meaning that you can perform the transaction and if it fails then the outcome will not occur.

Primary keys

• Primary keys are used to store and retrieve data
• Two types of keys:
  • Partition key
    • A unique attribute to the table (customer ID)
    • Partition keys input to an internal hash function that determines the partition
    (or physical location) of the data on the disk
    • This is why no 2 items have the same partition key, they can't have the same
    location in physical space on the disk
  • Composite key (partition key + sort key)
    • Combination of a partition key and a sort key
    • The unique combination required for a primary key means that we could
    have the same partition key used but by having different sort keys we have uniqueness

Restricting user access with IAM

User access can be restricted with a condition to an IAM policy to allow access to items only if the partition key value matches some unique ID.

Example configuration for user access control:

"Condition": {
    "ForAllValues:StringEquals": {
        "dynamodb:LeadingKeys": [
            "${www.mygame.com:user_id}" -> parition key must match user_id to restrict access
        ]
    }
}

Exam tips

• DynamoDB is a low latency NoSQL database
• Data models are either key-value or document formats (JSON, HTML, XML)
• Consistency models are eventually, strongly, or DynamoDB (ACID) transactions
• Features - consists of tables, items, and attributes
• 2 types of primary key - partition key, composite key (partition key + sort key)
  • Partition keys should be unique identifiers
  • Sort keys would be things like time stamps or dates to have a uniquely identifying
  primary key