dns alias

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Using aliases for datacenter dependencies

Scenario:

  • You have at least two datacenters running the same application and both datacenters are simultaneously active (business continuity)
  • Your application is mapped on a well-defined hostname (ie. www.myapplication.com)
  • On the first datacenter www.myapplication.com is running on IP a.b.c.d. One the second datacenter www.myapplication.com is running on IP x.y.z.t
  • You need to monitor your application health using IP addresses that are different from a.b.c.d and x.y.z.t

Solution:

  • Use GSLB.me in round robin balancing mode
  • Define one geohost that will be pointed by www.myapplication.com via a DNS CNAME record
  • Create two targets, one for each datacenter and define their aliases. Targets will be healthcheck-monitored using their IP addresses but GSLB.me will resolve the geohost name using the aliases.
  • Assign the relevant checks to each target
  • Configure the CNAME record on the primary DNS server that handles the domain myapplication.com

How to configure it:

  1. Register on GSLB.me and log on
  2. Select under which one of the available domains (gslb.us, gslb.info, …) you want to create your geohost. You can choose the domain you prefer, this is purely a “cosmetic” choice. Let’s choose mywebsite.gslb.eu
  3. Create your geohost: a geohost is the FQDN (Fully Qualified Domain Name) that your authoritative DNS will use as a CNAME for your application hostname (ie. www.myapplication.com). Select “Round robin” as your balancing algorithm. This will enable active-active distribution of incoming traffic towards your datacenters
  4. Define the first target: the target’s IP address is a.b.c.d and we are setting its alias IP address
  5. Select checks to be performed on the first target
  6. Define the second target: the target’s IP address is x.y.z.t and we are setting its alias IP address
  7. Select checks to be performed on the second target
  8. Configure your authoritative DNS to use a CNAME record to have www.myapplication.com point to mywebsite.gslb.eu
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    Slide1
    Go to http://go.gslb.me and logon. If you still don't have an account you can register and then logon.
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    Slide2
    Once logged in, let's create a sample geohost named mywebsite.gslb.eu. We can choose any top level domain among those shown on the left hand side of the GSLB.me interface.
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    Slide3
    Let's right click on the domain we choose in order to create a new geohost.
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    Slide4
    Next, we need to configure the geohost name (it will be prepended to the zone we selected in the previous step), set it to enable and select your balancing algorithm. We can configure DNS replies and TTL from here. When done, let's click on "Save" to save changes
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    Slide5
    After clicking on "Save" changes are committed and confirmation is displayed at the bottom of the screen.
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    Slide6
    After creating the geohost, we need to add targets: a target is the IP address of our application at each datacenter we are going to load balance. Let's right click on the geohost name and add the target from the popup menu that appears.
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    Slide7
    Let's now configure the IP address of our target, which is the IP address our application runs on the given datacenter. The alias IP address can be set here. This will enable GSLB.me to perform health-check monitoring using the target IP address and resolving DNS queries using the alias IP address. Checks schedule time can be set and the list of healthchecks to be performed is also configured here. Once done let's save the changes.
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    Slide8
    After clicking on "Save" changes are committed and confirmation is displayed at the bottom of the screen.
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    Slide9
    Let's now create our second geohost.
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    Slide10
    Let's now configure the IP address of our second target, which is the IP address our application runs on on the given datacenter. The alias IP address can be set here. This will enable GSLB.me to perform health-check monitoring using the target IP address and resolving DNS queries using the alias IP address. Checks schedule time can be set and the list of healthchecks to be performed is also config
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    Slide11
    After clicking on "Save" changes are committed and confirmation is displayed at the bottom of the screen.
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    Slide12
    Now we completed our geohost and targets configuration. We need to commit this setup to make it active. To do so, let's right click on the geohost name on the left hand side of the screen and commit the changes.
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    Slide13
    After committing changes a confirmation popup is displayed at the bottom of the screen.
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    Slide14
    We can now open the map to display our targets' geographical position and availability. Let's right click on the geohost name and open the map.
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    Slide15
    The map shows our targets positions and current availability. It is automatically refreshed every 5 seconds.
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    Slide16
    We can now open the status window to see the status of all geohosts and their targets. Let's right click on the geohost name and open the window.
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    Slide17
    The status window shows the health of our geohosts and targets. It is automatically refreshed every 5 seconds.
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    Slide18
    Let's now right click on the geohost name again to show the DNS entry we need to add to our authoritative DNS for the "myapplication.com" domain in this example.
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    Slide19
    In our example we will need to add to the "myapplication.com" DNS zone the entry "www.myapplication.com. 600 IN CNAME mywebsite.gslb.eu". This enables GSLB.me-based load balancing for your www.myapplication.com fully qualified domain name.
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