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DynamoDB

  • Fully managed, highly available with replication across 3 AZs
  • NoSQL database - not a relational database
  • Scales to massive workloads, distributed database
  • Millions of requests per seconds, trillions or rows, hundreds of thousands of TB of storage
  • It is fast and consistent regarding performance (low latency retrieval of data)
  • It is integrated with IAM for security, authorization and administration
  • It enables event driven programming with DynamoDB Streams
  • It provides auto scaling capabilities at low cost

Basics

  • DynamoDB is made of tables
  • Each table has a primary key (must be decided at creation time)
  • Each table can have an infinite number of items (rows)
  • Each item has attributes which can be added over time (can be null)
  • Maximum size of an item is 400KB
  • Supported data types:
    • Scalar types: string, number binary, null
    • Document types: list, map
    • Set types: string set, number set, binary set

Provisioned Throughput

  • Table must have a provisioned throughput, we must provision read and write capacity units
  • Read Capacity Unit (RCU): throughput for reads ($0.00013 per RCU)
    • 1 RCU = 1 strongly consistent read of 4 KB per second
    • 1 RCU = 2 eventually consistent read of 4 KB per second
  • Write Capacity Unit (WCU): throughput for writes ($0.00065 per WCU)
    • 1 WCU = 1 write of 1 KB per second
  • Option to setup auto-scaling of throughput to meet demand
  • Throughput can be exceeded temporarily using burst credits
  • If there are no more burst credits, we may get a "ProvisionedThroughputException" in which case it is advised to do exponential back-off retry

DynamoDB - DAX

  • DAX = DynamoDB Accelerator
  • Seamless cache for DynamoDB, no application re-write
  • Write go through DAX to DynamoDB
  • Micro second latency for cached reads and queries
  • Solves the Hot Key problem (too many reads on one value)
  • Each cache entry has a 5 minute TTL by default
  • We can get up 10 nodes per cluster for cache
  • The cache is multi AZ (3 nodes minimum recommended for production)
  • It is secure (Encryption at rest with KMC, VPC, IAM, CloudTrail)

DynamoDB Streams

  • Changes in DynamoDB (Create, Update, Delete) can end up in a DynamoDB stream - change log of everything happened in the table
  • This stream can be read by AWS Lambda, with which we can do some integrations:
    • React to changes in real time (example: welcome email to new users)
    • Analytics
    • Create derivative tables/views
    • Insert into ElasticSearch
  • We can implement cross region replication using Stream
  • Streams has 24 hours of data retention

DynamoDB - New Features

  • Transactions
    • All or nothing type of operations
    • We can coordinate insert, update and delete operations across multiple tables
    • Include up to 10 unique items or up to 4MB of data per transaction
  • On-demand
    • No capacity planning needed (WCU/RCU) - scales automatically
    • It is 2.5x more expensive than provisioned capacity
    • Helpful for spikes and unpredictable loads or if the application has a very low throughput

Security

  • We get VPC endpoints to access DynamoDB without internet
  • IAM policies
  • Encryption at rest using AWS KMS
  • Encryption at transit is handled by SSL/TLS
  • Backup and restore
    • DynamoDB provides point in time restores (just like any RDS)
    • Backup does not have any performance impact on the tables
  • Global tables
    • Multi region, fully replicated, high performance
    • Dynamo provides active-active replication
    • In order to be able to replicate data, DynamoDB Streams should be enabled

Migration

  • We can use DMS to migrate data to DynamoDB (from Mongo, Oracle, MySQL, st3, etc.)