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EIT_Network's avatar
Icon for Altostratus rankAltostratus
Dec 22, 2019

Active-Active Data Center

Dear Experts,


We are working on data center migration. Having 02 data Centers, few applications are active on DC-1 and some on DC-2. We are planning to have total 04 pairs of load balancer (2 pair in each data center , 01 pair in active-passive HA for MZ applications and 01 pair in active-passive HA for DMZ applications).


Load Balancer will be in Active-Active state (in both DC prospects). We are stucked / confused with GTM designing. below are the requirement where we are seeking suggestion.


1- GTM should redirect the end user traffic to respective DC where specific application is active. For eg : If application-1 is active on DC-2 then GTM should redirect the traffic to DC-2 (we beleive that Public DNS where CNAME entry (based on listeners IP.. has to be done is working with ROUND-ROBIN load balancing method only).

2- What are the other pre-requisite for above design.





2 Replies

  • Hamish's avatar
    Icon for Cirrocumulus rankCirrocumulus

    High level pre-reqs are simple


    1. Both DC's available from you client networks
    2. LTM and GTM
    3. Whoever is designing and implementing this must know how your apps work (It never goes well if this step is skipped, but sadly I find it often is)


    That doesn't tell you a great deal though. And I'm not sure how much detail you need or what exactly you're stuck on.


    1. What GTM needs is to be authoritative for whatever domain your'e using (I favour a subdomain like which has your application FQDN in it. And use a CNAME in your service domain).
    2. Secondly your GTM needs to be able to talk to your LTM's using the 3dns service. Your LTM's then report the status of the VS's up to GTM so GTM can use that information to decide where to resolve the queries to.
    3. Decide what algorithms you're going to use to dispatch at the GTM level.
    4. Implement it and test


    Note that GTM doesn't perform redirects. It performs DNS resolution. Your client asks their local DNS to resolve a name ( Using CNAMES as above your normal DNS resolves that to which is queried from the GTM server. GTM then looks at the request and matches it to a wideIP and the wide runs it via the chosen algorithms and out pops an IP (One of the VS's associated with the wideIP). The IP for that VS is then returned to the client. The client opens a TCP connection and (eventually) makes the query (HTTP/whatever)