6 - Cloud Apps and Load Balancing Flashcards
Three tier architecture for cloud app
Load balancing tier (spread)
App tier (process and respond)
Data tier (cache and handle db reqs)
Load balancing aims
Maximise throughput
Minimise response times
Avoid overload
Load balancing definition
Balance traffic across a group of devices
SLB
Server Load Balancer
SLBs are the _____ between servers and network
bridge
They understand higher layer protocols (and net protocols)
Benefit of SLB: Scalability
Capacity
Capacity is far greater than single server
Benefit of SLB: Availability
Health of real servers and apps monitored
Benefit of SLB: Manageability
Servers can be taken offline without downtime
Benefit of SLB: Security
Load balancers protect server farm from malicious users
Benefit of SLB: Quality of Service
Users can be provided service classes based on info in request packets
Stateless vs Stateful Load Balancing
Stateless - don’t track individual session
Stateful - track
Stateless Load Balancing Hashes
Use info in the IP packet: source IP, dest IP, source port and dest port
1: md5 packet header
2: mod that by n*# of paths
Stateful Load Balancing session tracking
Use a session table
Stateful Load Balancing Least Connections
Sends new requests to the server with least number of concurrent connections
Stateful Load Balancing Weight Distribution
Assign based on relative capacity of each server (weight)
Must be used with another message
