Service Redundancy and Traffic Balancing Using Anycast
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Anycast is a method of load balancing and high availability that uses dynamic routing protocols to direct client traffic to the optimal server that shares a common IP address. Each service is assigned an IP address that is configured on the loopback interface of multiple servers. Routers then determine the best server to terminate connections based on routing metrics. This allows traffic to be load balanced across servers and for connections to failover to alternate sites when primary servers fail.
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Service Redundancy and Traffic Balancing Using Anycast
- 1. Service Redundancy and Traffic Balancing Using Anycast Sean Jain Ellis [email_address] Twitter @bandarji
- 2. Traditional Load Balancer Function Balances connections between servers Routes requests to healthy systems Handles site failure
- 3. What is Anycast? Anycast is a method by which dynamic routing protocols are used to direct traffic to the best candidate server or servers within a group of potential destinations, all sharing the same address. Benefits High availability Load balancing Consistent configuration Dispersed deployment
- 4. Really, what is Anycast? Each service assigned an address Same address applied to all servers on loopback Servers advertise host route to loopback address Servers become routers, integrating with infrastructure Use zebra or quagga software daemons Ethernet interface becomes gateway for upstream routers Regardless of location Refer client connections to service address Routers determine server to terminate connections
- 5. Anycast Addressing All servers share logical address 172.17.13.10.
- 6. Routers As Load Balancers Traffic directed to destination with least cost When two or more destinations are equal Select gateways by round robin algorithm Maintain connection table, ensuring server affinity When low cost destinations disappear Select gateway(s) to destination of equal, higher cost Listen for returning low cost routes Why not? The hardware is already present
- 7. 油
- 8. What You Need Routing protocol daemon zebra or quagga Tool to monitor service monit, netcat, curl Coordination from network team Routing protocol parameters SNMP access Console (administrative) access too much to ask?
- 9. Server Configuration First: define logical addressing scheme Determine routing protocol Assign an address for service Configure loopback interface with service address Configure routing protocol on server
- 10. Server Configuration in Detail Example is for CentOS host using quagga from EPEL /etc/sysconfig/network-scripts/ifcfg-lo:[0-x] /etc/quagga/zebra.conf /etc/quagga/ospfd.conf
- 11. Sample /etc/quagga/zebra.conf hostname ServerA interface lo:0 油 ip address 172.17.13.10/32 interface eth0 油 ip address 172.17.13.40/27
- 12. Sample /etc/quagga/ospfd.conf hostname ServerA interface eth0 油 ip ospf authentication message-digest 油 ip ospf message-digest-key 1 md5 apasswd 油 ip ospf priority 0 油 ip ospf hello-interval 1 油 ip ospf dead-interval 4 router ospf 油 ospf router-id 172.17.12.40 油 area 94.40.30.0 authentication message-digest 油 network 172.17.13.10/32 area 94.40.30.0 油 network 172.17.12.32/27 area 94.40.30.0
- 13. Routing Must Be Per-Flow JUNOS set policy-options policy-statement ecmp then load-balance per-packet set routing-options forwarding-table export ecmp edit forwarding-options hash-key family inet 油 set layer-3 油 set layer-4 cisco IOS int gi0/0/0 油 ip load-sharing per-destination router ospf 1 油 maximum-paths 8 ip cef accounting load-balance-hash
- 14. Standby Host Failure of the server(s) on Network One causes routing to switch to server(s) on Network Two. Network One could be a single system with server in Network Two serving as a standby host, if per-flow routing is not an option.
- 15. Failure Recovery OSPF hello packets One second interval Dead timer of four seconds Faster? Use bidirectional forwarding detection (BFD)
- 16. OSPF vs BGP vi vs emacs Go with whatever network folks offer However! BGP allows for server-side policies to control traffic OSPF traffic controls are configured per router interface
- 17. Thank You Sean Jain Ellis [email_address] Twitter @bandarji
Editor's Notes
- #14: show route table inet 172.17.13.10 show route forwarding-table family inet destination 172.17.13.10 # show ip cef 172.17.13.10 internal # show ip cef 172.17.13.10 interface # show ip cef # show cef interface gix/x/x