llb

(L)ittle(L)oad(B)alancer, a dead simple event-driven load-balancer. Supports Linux (and arguably OSX) through epoll and poll/select (kqueue on BSD-like) as fallback, it uses an event-loop library borrowed from Sol.

Written out of boredom/learning purpose (50/50) during self-isolation. Sure thing there will be bugs and plenty of corner cases to be addressed.

Features:

• Logging
• Configuration file on disk
• Basic healthcheck for backends
• TLS encryption (to be refined)
• Daemon mode
• Multithread event-loop
• HTTP and TCP load-balancing
• Round-robin, weighted round-robin, hash-balancing, random-balancing, leastconn, leasttraffic
• Pretty small (~2000 sloc) and little dependencies (openssl)

Next:

• Improvements on all previous points

Build

Dependencies

• gcc
• make
• cmake
• OpenSSL (libssl-dev)

$ cmake . && make

Quickstart

Backend servers at http://localhost:8080 and http://localhost:8081, balancing strategy WEIGHTED-ROUND-ROBIN

$ ./llb -v -b http://localhost:8080:2,http://localhost:8081:4 -l weighted-round-robin

A simple configuration can be passed in with -c flag:

$ ./llb -c path/to/llb.conf

As of now the configuration is very small and self-explanatory, default path is located to /etc/llb/llb.conf:

# llb configuration file, uncomment and edit desired configuration

# accepts http | tcp
mode http

# Load-balancing settings

# Frontends are the endpoint exposed as entry point for connecting clients
frontends 127.0.0.1:8789,127.0.0.1:8790,127.0.0.1:8791

# Backends is a pool of server to load-balance requests from clients
backends 127.0.0.1:6090,127.0.0.1:6090,127.0.0.1:6090

# Set round robin as balancing algorithm
# Other options available can be
# random-balancing | hash-balancing | leastconn | leasttraffic | weighted-round-robin
load_balancing round-robin

# Logging configuration

# Could be either DEBUG, INFO/INFORMATION, WARNING, ERROR
log_level DEBUG

log_path /tmp/llb.log

# TCP backlog, size of the complete connection queue
tcp_backlog 128

# TLS certs

#cafile certs/ca.crt
#certfile certs/alaptop.crt
#keyfile certs/alaptop.key

# TLS supported versions
#tls_protocols tlsv1,tlsv1_1,tlsv1_2,tlsv1_3

Executable accepts some simple arguments, in case of a configuration file specified every setting is overridden by it.

• -h print an usage help
• -v enable verbose debug messages
• -d run in daemon mode
• -c <path/to/conf> specify a configuration path, defaults to /etc/llb/llb.conf
• -l <load-balancing-algorithm> specify a load-balancing algorithm to be used. Choices are round-robin, hash, random, leastconn, leasttraffic and weighted-round-robin
• -m <mode> choose the run mode between tcp and http. Defaults to http
• -b <host:port:weight>,<host:port:weight>.. add backend machines with a weight associated, it will be ignored for load-balancing algorithms other than weighted-round-robin