This document discusses different approaches to managing multiple data centers for high availability and resilience. It describes four approaches: 1) Active/passive where only one data center is active, 2) Active/active application tiers with active/passive database, 3) Mostly active/active application and database tiers, and 4) Full active/active across all tiers. It also discusses challenges like concurrent logins and the need for global server load balancers to intelligently route traffic between data centers.

1. Ashwinee Kumar
Nov 2015
Data Center
Ecommerce Series – Part 4

2. Data Center
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3. Data Center
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• Two or more data centers helps to ensure availability by providing resiliency
against
• natural disasters
• human errors
• upstream outages
• software problems cut.

4. Challenges with multi Data Center model
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1. Concurrent user login leading to data corruption – two family member
logging in
2. Logic for routing traffic to either one of the multiple DC’s
a) DNS server can have multiple records one for each DC
b) Intelligent system called GSLB
c) CDN that offers GSLB

5. Data Center Approach 1 – Active/Passive
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Only one Data Center (Application and DB tier) is active
a) DC failure will lead to lengthy downtime as passive DC has to be
brought grounds up
b) Low cost of ownership

6. Data Center Approach 2 – Active/Active Application Tiers,
Active/Passive Database Tiers
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Two or more data centers fully built up and operating independently, with only
the database being active/passive.
a) Negligible recovery time
b) Higher cost of ownership
c) Delay in DB writes in one of the DC

7. Data Center Approach 3 – Active/Active Application Tiers,
Mostly Active/Active Database Tiers
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Two or more data centers fully built up and operating independently
a) Negligible recovery time
b) High cost of ownership
c) Additional logic to handle real time DB sync

8. Data Center Approach 4 – Full Active/Active
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Two or more data centers fully built up and operating independently, with only
the database being active/passive.
a) Negligible switch over time
b) High cost of ownership
c) Additional logic to allocate DC to user who has already logged in

9. GSLB
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10. GSLB – Global Server Load Balancer
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1. Directing customers to the closest data center best able to service their
requests
2. Making the concurrent login problem much less likely to occur
3. You can personalize the experience for customers.
4. You may need to restrict certain functionality based on the physical
location of a customer.
5. You can roll out functionality slowly - city by city for instance
6. Health checking of key components of application