dhruvsha256 / load-balancer

Layer 4 Load Balancer from scracth in Python

Load Balancer

• my implementation of a layer 4 load balancer with health checks in python.
• currently Round Robin server selection algorithm is supported.

Demo

• edit config.json
• run multiple servers on port defined in config.json in different terminal windows

# like this
python server.py 5001 # in one window
python server.py 5002 # in another window

• run load balancer

python loadbalancer.py PORT

• make a request to load balancer

curl localhost:PORT

• requests will be redirected to any of running backend server.
• if a server missed heartbeat of is offline, no new request will be sent to it.
• if a server came back online, new requests will be redirected to it.
• you can see asciicast

Load Balancer vs Reverse Proxy

• Load Balancer is a Reverse Proxy with additional bells and whistles.

Layer 4 vs Layer 7 load balancer

Layer 4 Load Balancer

• Cant see the data of request, only binary.
• Data may be compressed, encrypted.
• It can only see src and dest ip.
• Change dest ip to server using NAT.
• Only one tcp connection.

Layer 7 Load Balancer

• Can see the data of request and based on that redirects request.
• Like sending to server based on user id.
• Client request -> lb (can change request, add headers etc etc) -> lb make new request to server.

Load Balancing Algorithms

• Round Robin.
• Weighted Round Robin.
• Lease Connection First.
• Lease Response Time First.
• Hash Based.