...
Azure offers many load balancing solutions , and these products could be used as a load balancer options. These options are not directly supported by ESRI and the EGIS team would be responsible for supporting these options (with the help of our Microsoft colleagues).
Traffic manager
Azure traffic manager is a simple DNS switch that can route to a pool of public addresses. The priority and distribution of network traffic can be defined in many ways. A traffic manager is crucial in the implementation of disaster recovery and will be in place in our production instance.
...
Comparing uptimes of each approach
Service | % Uptime | Minutes down/30days |
|---|---|---|
VM | 99.9% | 43.83 |
App Gateway | 99.95% | 21.92 |
Load Balancer | 99.99% | 4.38 |
Traffic Manager | 99.99% | 4.38 |
-- | -- | -- |
Paired VMs [1] | 99.95% | 21.92 |
...
Uptime percentages were converted to downtimes using the table found on Wikipedia's page on high availability
Calculating an overall SLA
If we treat each tier independently, which is a worst-case assumption, we can calculate an overall system uptime by multiplying each component uptime ref . Downtime per month is calculated using http://www.slatools.com/sla-uptime-calculator. This yields an estimated overall uptime as follows:
TM | IIS LB | WEB | POR | GIS | DS | Overall Uptime | Overall downtime/month |
|---|---|---|---|---|---|---|---|
99.99% | 99.90% | 99.95% | 99.95% | 99.95% | *99.99%90% | 99.78%64% | 95min155.5min |
TM | Azure LB | WEB | POR | GIS | DS | Overall Uptime | Overall downtime/month |
|---|---|---|---|---|---|---|---|
99.99% | 99.99% | 99.95% | 99.95% | 99.99%95% | *99.90% | 99.87%56min73% | 117min |
* Since our DS0 machine currently hosts the file share used by paired portal and gis machines, we can’t consider it a load balanced resource
Case study
We've recently deployed a production-style instance in Bill's sandbox, TC-Sandbox-BXUeGIS-RG. This instance has a virtual machine load balancer in front of the two web machines, and also has a traffic manager and load balancer configured.
VM load balancer: https://tstweb.tcgis.ca/portal/home/
Azure load balancer: https://tst-tm.tcgis.ca/portal/home/
Open question
Given a Treasury Board preference to consider cloud-first, but ESRI's lack of specific support for 3rd party load balancers, which option do we choose? What do we need to do to feel comfortable with using an Azure load balancer?
...