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Synopsis:
This guide contains instructions on how to set up round robin DNS. Round robin DNS with polling, is used for load balancing and fail over.
E.g.- If you have a website mirrored on three servers, round robin DNS will distribute requests evenly between those servers. 'Polls' (HTTP, PING, IMAP, etc.) are set up to test the responses at intervals, usually 60 seconds. If any of the responses fail, the record is removed from the round robin until the connection to the resource can be established again.
Prerequisites:
1. For the example below, you require three sensors which means you must have an active DNS Hosting Premier (6 sensors) account or above, with Entity Data. NB: Two sensors are provided on DNS Hosting Power, which is sufficient if you only need fail over between two servers.
How-to Steps:
In this example, you have a website mirrored on three different servers and you want to set up fail over so that if one server becomes unavailable the load will be distributed between the remaining two.
1. You need to make sure all three A records have the same name but different IP addresses:
www.yourdomain.com > 10.0.0.101
www.yourdomain.com > 10.0.0.102
www.yourdomain.com > 10.0.0.103
2. Then, you would set up polls. In DNS Zones, click 'DNS Round Robin' and then click 'Add new poll'.
3. Here is an example of what to put in the fields:
Name = Poll-1 (or any name you prefer to identify the poll)
Tested protocol = HTTP (as we are testing for webpage availability in this case)
Monitoring interval = 1 minute(s) (how often the resource is tested)
Tested resource = 10.0.0.101 (IP or name of resource you are testing for availability)
Try resource for = 10 seconds (how long the resource is tested for before being removed from, or added back in to the round robin)
4. You then need to mark the check boxes for the other two A records from your round robin, in the list at the bottom:
[x] www.yourdomain.com > 10.0.0.102
[x] www.yourdomain.com > 10.0.0.103
And then click 'Apply Changes', then 'OK'.
This will ensure that if 10.0.0.101 becomes unavailable, the load will be distributed between 10.0.0.102 & 10.0.0.103.
5. You need to repeat this process for the remaining two IP addresses. Altogether, you would set up the following:
Poll1 with 10.0.0.101 as the 'tested resource' and then select the A records for the other 2 servers using the check boxes below and click apply changes.
Poll2 with 10.0.0.102 as the 'tested resource' and then select the A records for the other 2 servers using the check boxes below and click apply changes.
Poll3 with 10.0.0.103 as the 'tested resource' and then select the A records for the other 2 servers using the check boxes below and click apply changes.
This will ensure that if any of the servers are unavailable, the request will be sent to one of the other servers.
Please also refer to the help section in DNS Manager, at the top right of the screen, for further information before submitting a ticket.
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