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| Failover across subnets using overlay IP | ||
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clusters let you fail over IPs - and thereby, the application configured for HA - between different subnets in the same AZ or in different AZs.
The following information is required:
The overlay IP address to be used for failover
The device to which the IP should be plumbed
The directory in which the AWS CLI is installed; this input is not required if it is provided in the PATH environment variable
AWS does not allow the private IP of one subnet to be failed over to a different subnet. To overcome this limitation, provides an overlay IP, which is defined at the VPC level, so that it can be used across subnets.
The following graphic depicts a sample failover configuration across subnets within the same AZ using an overlay IP:
The sample configuration includes the following elements:
A virtual private cloud (VPC) is configured in Region A of the AWS cloud.
An application is configured for HA using an cluster that comprises two nodes, Node 1 and Node 2, which are EC2 instances.
Node 1 exists in Subnet 1 and Node 2 exists in Subnet 2.
An overlay IP is configured, which allows the private IP of a node to be failed over from one subnet to another in an AZ as part of the failover or the failback operations.
The following snippet is a service group configuration from a sample VCS configuration file (main.cf):
group appnetworkSG (
SystemList = { ip-172-34-20-109 = 0, ip-172-34-30-231 = 1 }
AutoStartList = { ip-172-34-20-109, ip-172-34-30-231 }
)
AWSIP AwsIp_Res (
OverlayIP = "172.35.1.3/32"
Device = eth0
AWSBinDir = "/usr/local/bin"
)
IP Ip_Res (
Device = eth0
Address = "172.35.1.3"
NetMask = "255.255.255.255"
)
NIC Nic_Res (
Device = eth0
)
AwsIp_Res requires Ip_Res
Ip_Res requires Nic_Res
The following graphic depicts a sample failover configuration across subnets in different AZs using an overlay IP:
The following snippet is a service group configuration from a sample VCS configuration file (main.cf):
group appnetworkSG (
SystemList = { ip-172-34-20-109 = 0, ip-172-34-30-231 = 1 }
AutoStartList = { ip-172-34-20-109, ip-172-34-30-231 }
)
AWSIP AwsIp_Res (
OverlayIP = "172.35.1.3/32"
Device = eth0
AWSBinDir = "/usr/local/bin"
)
IP Ip_Res (
Device = eth0
Address = "172.35.1.3"
NetMask = "255.255.255.255"
)
NIC Nic_Res (
Device = eth0
)
AwsIp_Res requires Ip_Res
Ip_Res requires Nic_Res