AWS Community Day 2022 Gautam Singh Getting Frugal with DynamoDB

1. Being frugal with DynamoDB
Gautam Singh | @singhkgautam

2. The Backstory
• Lead the migrations of DynamoDB tables from
On-Demand to Provisioned Capacity mode for
one of the biggest retailer in North America
• The goal was to save cost
• Individual Tables Containing an excess of 1
billions items (+1 TB)
• Over 100K items added every day
• Used by multiple microservices servicing million
plus users

3. Reference Architecture
Producer
Producer
Producer
Consumer
Consumer
Consumer
Microservices
Microservices
Microservices
Microservices
Microservices

4. Let’s cover the basics

5. Unit of measure for R/W Capacity
• 1 RRU/RCU ≡ 1 strongly consistent or 2 eventually
consistency read of an item up to 4KB
• 2 RRU/RCU ≡ 1 transactional read of item up to 4KB
• 1 WRU/WCU ≡ 1 write for item up to 1 KB
• 2 WRU/WCU ≡ 1 transactional write for item up to 1
KB

6. On-Demand Capacity Mode
• Pay Per Request pricing
• Only pay for what you use
• Capable of serving thousands of requests /second
• Single digit millis SLA
• Low utilization ratio

7. When to use On-Demand mode
• Un-Predictable or unknow traffic.
• Mission critical application demanding single
digit millis response time
• Your organization is still using manual
provisioning methods or in initial stage of
DevOps maturity level

8. Provisioned Capacity Mode
• Configure your provision RW capacity
• Pay for the provisioned capacity
• Can be used with auto scaling
• Predictable cost

9. When to use Provisioned mode
• Predictable application traffic.
• Traffic is consistent or ramps gradually.
• You can forecast capacity requirements to
control costs.
• High utilization ratio
• Can tolerate throttling
• Cost gain justifies the additional overhead
• Your organization is in advance stage of DevOps
maturity level

10. How Scaling Works

11. Demo

12. So how we did it?

13. Before you begin
• Is it worth the hassle?
• Average/Median RW rates
• Peak RW rates
• Promotional or seasonal peaks
• Most accessed partition key
• Hot partitions
• Response time SLA
• Acceptable error rate

14. Before you begin

15. Is it worth the hassle?

16. Understand Traffic Pattern
Consumed Write Capacity
Consumed Read Capacity

17. Cost Analysis

18. On-Demand Pricing
Write Request Units (WRU) $1.25 per million
Read Request Units (RRU) $0.25 per million
Consumed WRU per minutes 500
Consumer RRU per minutes 1000
Consumed WRU per month 500 X 60 X 24 X 30 = 21.6 million
Cost for WRU per month 21.6 X $1.25 = $27.00
Consumed RRU per month 1000 X 60 X 24 X 30 = 43.2 million
Cost for RRU per month 43.2 X $0.25 = $10.8
Total Cost per month $27.00 + $10.8 = $37.80

19. Provisioned Pricing
Write Capacity Units (WCU) $0.00065 / WCU per hour
Read Capacity Units (RCU) $0.00013 / RCU per hour
Min WCU 10
Max WCU 125
Min RCU 25
Max RCU 300
Avg WCU Consumed .8 X 10 + .2 X 62.5 = 20.5
Cost for WRU per month 20.5 X 24 X 30 X $0.00065 =
$9.594
Avg RCU Consumed .6 X 25 + 0.4 X 150 = 75
Cost for RCU per month 75 X 24 X 30 X $0.0003 = 7.02
Total Cost per month $9.594 + 7.02 = $16.614

20. Capacity Planning

21. Gather Historical Data
• Traffic pattern
• Average/Median RW rates
• Peak RW rates
• Promotional or seasonal peaks
• Most accessed partition key
• Hot partitions
• Response time SLA
• Acceptable error rate

22. Fine tuning the Capacity
Metrics

23. Scaling Gotchas and Limitation

24. Application Tuning

25. Monitoring & Alerting

26. Handling Cloud Watch Alerts

27. Automation

28. Optimization Hacks
• Upfront planning for your seasonal peak load
• Use On-Demand mode for Non-Prod environment
• Schedule your scaling event
• Switch between On-Demand and Provisioned
Mode with ease

29. Questions?