This document discusses high availability configurations for load balancers, especially for small companies. It presents options for dedicated servers in a data center using hardware load balancers or virtual IP addresses. It also discusses using Elastic Load Balancing and Elastic IP addresses on AWS. Key points covered are: - Hardware load balancers can provide high availability but are an expensive solution, while virtual IP addresses require checking a load balancer's failover time. - On AWS, Elastic Load Balancing supports auto-scaling but doesn't support fixed IP addresses, while Elastic IP addresses can be associated and released like a virtual IP. - Both ELB and EIP on AWS require ongoing payment, and neither can be used within internal AWS

1. HA of Load Balancer
for Small Company
charsyam@naver.com

2. Agenda
• Why?
–DNS RoundRobin
• Dedicated Server in IDC
–Hardware L4
–Using VIP
• AWS
–Using EIP

3. Why?
• Let’s see in beginner’s point of view.
– How to distribute clients’ requests.
Using DNS RR
CLIENT
CLIENT Web Server
DB
CLIENT Web Server
CLIENT

4. Why?
• Let’s see in beginner’s point of view.
– How to distribute clients’ requests.
– But If one web server dies, half requests will fail.
– And DNS RR needs lots of propagation time.
Using DNS RR
CLIENT
CLIENT Web Server
DB
CLIENT Web Server
CLIENT

5. Load Balancer!
• LB distributes clients’ requests.
Using Load Balancer
CLIENT
CLIENT Web
LB DB
CLIENT Web
CLIENT

6. Load Balancer!
• LB distributes clients’ requests.
– If one web server dies, LB will get rid of failed server.
Using Load Balancer
CLIENT
CLIENT Web
LB DB
CLIENT Web
CLIENT

7. Load Balancer FAIL
• If LB dies, It is critical disaster.
– So we need HA of Load Balancer.
Using Load Balancer
CLIENT
CLIENT Web
LB DB
CLIENT Web
CLIENT

8. How?
• How to HA of LB
– It depends on your situation.
• Question?
– Where do you host your service?
• IDC, aws
• Let’s go to build.

9. Dedicated Server in IDC
• Using Hardware L4
– Could your hosting service support Hardware L4
– Pros
• The easiest way to manage
– Cons
• Expensive solution.
• Using VIP
– With HAProxy or Nginx

10. Hardware L4 #1
• You can choose 2 types of solution.
• Using L4 as LB
Using Hardware L4 #1
CLIENT
CLIENT Web
L4 DB
CLIENT Web
CLIENT

11. Hardware L4 #2
• Using L4 with LB
– Hardware L4 can fail, but rarely
Using Hardware L4 #2
CLIENT
CLIENT LB Web
L4 DB
CLIENT LB Web
CLIENT

12. Using VIP
• Virtual IP Address
CLIENT
1.1.1.4
Route
1.1.1.2
1.1.1.2 1.1.1.3
1.1.1.4
1.1.1.4 is VIP which is allocated 1.1.1.2

13. Using VIP
• We can give VIP to other Server.
CLIENT
1.1.1.4
Route
1.1.1.2 1.1.1.3
1.1.1.4
1.1.1.4 is VIP which is allocated 1.1.1.2

14. Software LB with Keepalived
• Virtual IP Address( HAProxy, Nginx doesn’t matter )
192.168.1.2 Web Web
LB1 LB2 192.168.1.10 192.168.1.11
192.168.1.3
Haproxy
192.168.1.4
Haproxy
Web DB
keepalived keepalived 192.168.1.12 192.168.1.100

15. Software LB with Keepalived
• But you have to check failover time.
192.168.1.2 Web Web
LB1 LB2 192.168.1.10 192.168.1.11
192.168.1.3
Haproxy
192.168.1.4
Haproxy
Web DB
keepalived keepalived 192.168.1.12 192.168.1.100
Keepalived checks each other.
And LB2 Keepalived reassign VIP
to oneself.

16. Software LB with Keepalived
• Link
– HAProxy with keepalived
• http://haproxy.1wt.eu/download/1.3/doc/architecture.txt
• http://andyleonard.com/2011/02/01/haproxy-and-keepalived-example-
configuration/
• http://aaronwalrath.wordpress.com/2011/06/28/configure-haproxy-and-
keepalived-for-load-balancing-and-reverse-proxy-on-red-
hatscientificcentos-linux-56/
– Nginx with keepalived
• http://www.cyberciti.biz/faq/handling-nginx-failover-with-keepalived/
• http://evolution.voxeo.com/wiki/kb:swloadbalancingfailover

17. AWS
• What are different from IDC
– You can’t use Hardware L4
– You can’t use multicast
– You can’t use VIP
• How?
– ELB( Elastic Load Balancer )
– EIP( Elastic IP )

18. ELB
• Auto Scaling is possible.
• ELB doesn’t support Fixed IP.
CLIENT
CLIENT EC2 Instance
ELB
CLIENT EC2 Instance
CLIENT

19. EIP
• Elastic IP Address
• We can associate and release EIP like VIP

20. Weakness of ELB,EIP
• Whenever we use it, we have to pay.
– It is external IP.
• And it is impossible to apply ELB,EIP in AWS internal
networks.

21. How to Handle in AWS?
• There is no Silver Bullet.
• DNS based Solution
– Using Dynamic DNS Server for internal Network.
– Using short TTL.

22. Thank you!