The Doppler Quarterly Spring 2016 | Page 11

“ We needed to migrate two mission-critical applications with zero downtime .”
Additionally , creating a test plan to account for all possibilities was difficult , as legacy applications are often not fully understood , and not all dependencies and application behaviors are known .
Infrastructure Background
Application 1 :

“ We needed to migrate two mission-critical applications with zero downtime .”

• Two Windows Servers hosting Web and Java services in a cluster configuration for high availability
• Back end apps and services
• A Citrix NetScaler load balancer used in front of the application servers
Application 2 :
• Three Linux servers hosting a Web server
• A two node DB cluster on Linux servers
• A Citrix NetScaler load balancer used in front of the application servers
Migration Options and Challenges
The migration team considered various options including installing parallel instances of applications in AWS , and using load balancers and DNS to cut over to the new instances . Very quickly we realized that it would take a considerable effort to install a parallel instance of the applications .
The challenges included licensing implications , legacy versions of products , supportability to install
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