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Zen

My Load Balancer written in C.

Inspiration

  • I am looking to expand my knowledge in distributed systems, one project at a time. So far I covered Sentinel, a distributed KV storage which covered consensus algorithms, distributed networking, etc.
  • I am looking to create a load balancer and database from scratch and maybe create a large-scale distributed system leveraging these components.

Topics

  • Languages: C
  • Concepts:
    • Techniques: Multi-threading, HTTP and TCP load-balancing
    • Algorithms: (Weighted) Round-Robin, Hash/Random-Balancing, Least Connections/Traffic,
    • Networks: TLS encryption
    • Other: Logging, Daemon mode

Build

Dependencies

  • gcc, make, cmake, OpenSSL (libssl-dev)
$ cmake . && make

Quickstart

Covers a bit of architecture...not that it is that verbose.

Backend servers at http://localhost:8080 and http://localhost:8081, balancing strategy (weighted)-Round-Robin

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

Simple config can be passed with -c:

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

Config is very small and self-explanatory, default path located to lib.conf:

# zen 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/zen.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 simple args, in case of config overwriting 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/zen/zen.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