Floating private IP across Availability zones

Question

Hi,

We are trying to achieve High availability for our SIP Proxy. We intend to set two SIP proxies in two availability zones in the same UK region in Active/Standby. The SIP proxies will front a cluster of Asterisk PBXes on a private network.

For the public interface to SIP clients it is straightforward we can simply use an Elastic IP for the public IP and swap it from one AZ to another. However on the private interface to the PBX cluster we are stuck. The private IPs are secondary IP addresses on the main interface currently and have to be on the subnet for that AZ so we can't just swap a network interface. We have seen some blog posts where it is suggested to use a private IP address which is outside the VPC CIDR range and add it to routing tables. However it is not possible to add this IP to any network interfaces so it can't be used to route out.

Hopefully someone knows a solution to this issue.
Thanks

tech74 · Answer

Our SIP proxy is already acting as a load balancer for the Asterisk servers. These third party load balancers don't work in this environment as they need to be SIP aware

Steve Kinsman · Answer

Can your clients using the private IPs use a domain name rather than IP address?  Then you can programmatically update the Route 53 record set for that domain, changing the A record's IP address mapping.  We've often used this approach for HA with an Auto Scaling Group with max=1, for workloads where brief outages are acceptable.

Tom Rosenfeld · Answer

See this AWS whitepaper [Real-Time Communication on AWS](https://docs.aws.amazon.com/whitepapers/latest/real-time-communication-on-aws/floating-ip-pattern-for-ha-between-activestandby-stateful-servers.html) It has a chapter on "Floating IP pattern for HA between active–standby stateful servers"

Floating private IP across Availability zones

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