How backup servers work in the Balancer
In any high availability environment, you’ll always encounter backup servers which will take over traffic/services when the primary servers die or fail.
And this is exactly why we’ve added functionality into Snapt that allows the ability to mark your backend servers with “Primary” or “Backup”.
When adding servers to your group or through backend management you will notice that there is an option to set Server Type to “Primary” or “Backup”
Option 1 – Default
During an outage of your backend servers, when all your “Primary” servers are offline, Snapt will bring up your first Backup Server and serve traffic to that server.
Please note that in this configuration, only 1 Backup server is brought online even if you have more than one backup configured in the pool.
If the first backup server were to go down, then Snapt will bring up the next available Backup Server.
Option 2 – All Backups
With this option, you will be able to specify that all your Backup servers should be made Active once all your “Primary” servers have failed.
To set this option, navigate to your Group > Edit > Backup Servers > All Backup to “On”
OR
Backend Management > Edit > Backup Servers > All Backup to “On”
Option 3 – Failover to Backup Pool
With this option, we will failover to a backup pool if the production pool does not have sufficient capacity.
This involves adding an ACL that checks how many backend servers are online, and if it drops below your specified threshold, Snapt will then send the traffic to your Backup Pool
Step 1: Create your second backend (backup pool)
Balancer > Backend Management > Add a Backend
Step 2: Create ACL
Balancer > ACL Management > Add ACL
Replace value (integer) with your preferred number. With the current screenshot below, we’re matching with 2 or fewer backend servers.
Step 3: Attached to Frontend
Balancer > Frontend Management > Attach ACL
For ACL Action we’ll use “use_backend” and select the Backend you created on Step 1
For ACL 1 select the ACL you created on Step 2
Option 4 – Failover to Backup Pool with Backup Servers
With this option, we’ll failover to a backup pool if the production one does not have enough capacity, secondly, we want to use backup servers when all primary servers from the backup pool are DOWN
For this method, we’ll follow Option 3, but we’ll mark our Server Type for the Backup Servers as “Backup”
We can also toggle the “All Backup” option to “On” if we’d like to have a hybrid of Option 2 and Option 3