Design: How Does LoadBalancer Work?
Similar Posts:
- Typical Features/Considerations
| Name | Summary |
|---|---|
| Route traffic | LoadBalancer Algorithms |
| L3/L4 LoadBalancer vs L7 LoadBalancer | link |
| Redundant Load Balancers | Load balancer active/passive |
| Health checks | Load balancers should only forward traffic to “healthy” backend servers |
| Sticky session | |
| SSL termination | |
| Service throttling | |
| Predictive analytics | Smart load balancers can help to determine traffic bottlenecks |
Q: How LoadBalancer route requests?
Typical algorithms:
| Name | Summary |
|---|---|
| Round robin | |
| Weighted round robin | Servers with higher weights get more connections |
| Least Connection | |
| Least Response Time | |
| Least Bandwidth | |
| IP Hash | Caculate IP hashing, then decide a server |
Commonly used algorithms for HAProxy(link):
- roundrobin: Round Robin selects servers in turns. This is the default algorithm.
- leastconn: Selects the server with the least number of connections–it is recommended for longer sessions. Servers in the same backend are also rotated in a round-robin fashion.
- source: This selects which server to use based on a hash of the source IP i.e. your user’s IP address. This is one method to ensure that a user will connect to the same server.
Q: What are the pros/cons of different algorithms? And typical use cases of each?
A: TODO
Q: L3/L4 LoadBalancer vs L7 LoadBalancer
- L3/L4 Load Balancer: traffic is routed by IP address and port. L3 is network layer (IP). L4 is session layer (TCP).
- L7 Load Balancer: traffic is routed by what is inside the HTTP protocol. L7 is application layer (HTTP).
Q: What are sticky sessions?
Some applications require that a user continues to connect to the same backend server. This persistence is achieved through sticky sessions, using the appsession parameter in the backend that requires it.
Q: How the Readiness Probe is done for backend services?
Often, session tracking is accomplished via a consistent hashing function.
Q: How loadbalancer enable/enable one specific backend server, per health check?
A: TODO
Q: Elastic IP vs loadbalancer?
A: TODO
Q: For the failure of loadbalancer, would people add more than one redundant load balancer?
A: TODO
Q: Consistent hashing in load balancing?
A:
Configuration example in HAProxy or in the ALOHA Load-Balancer: link
balance source hash-type consistent