Galera Load Balancer (glbd)

The Galera Load Balancer (glbd) is no longer under active development. It is provided here for historical and reference purposes only. For new deployments, we recommend using a modern, fully supported proxy such as MariaDB MaxScale.

Galera Load Balancer (glbd) is a simple, multi-threaded TCP connection balancer, optimized for database workloads.

It was inspired by pen, but unlike it, GLB focuses only on balancing generic TCP connections.

Features

Feature	Description
Server Draining	Remove servers smoothly without interrupting active connections.
High Performance	Uses Linux epoll API (2.6+).
Multithreading	Leverages multi-core CPUs for better performance.
Optional Watchdog Module	Monitors server health.
Seamless Client Integration	Uses libglb for load balancing without changing applications, by intercepting connect() calls.

Installation

GLB must be built from source. There are no pre-built packages.

git clone https://github.com/codership/glb
cd glb/
./bootstrap.sh
./configure
make
sudo make install

This installs:

• glbd (daemon) → /usr/sbin

• libglb (shared library)

Running as a Service

To run as a service:

# cp files/glbd.sh /etc/init.d/glb
# cp files/glbd.cfg /etc/sysconfig/glbd.cfg   # Red Hat / CentOS
# cp files/glbd.cfg /etc/default/glbd.cfg     # Debian / Ubuntu

Manage with:

service glb start|stop|restart|getinfo|getstats|add|remove|drain

Configuration

GLB can be configured either via command-line options or via a configuration file.

Command-Line Options {#command-line-options}

glbd --help

Configuration File (glbd.cfg)

Parameter	Description
LISTEN_ADDR	Address/port GLB listens on for client connections
DEFAULT_TARGETS	Space-separated list of backend servers
OTHER_OPTIONS	Extra GLB options (e.g. balancing policy)

Example:

# Galera Load Balancer Configuration
LISTEN_ADDR="8010"
DEFAULT_TARGETS="192.168.1.1 192.168.1.2 192.168.1.3"
OTHER_OPTIONS="--random --top 3"

Destination Selection Policies

GLB supports five policies:

Policy	Description
Least Connected(default)	Routes new connections to the server with the fewest active connections (adjusted for weight).
Round Robin	Sequentially cycles through available servers.
Single	Routes all connections to the highest-weight server until it fails or a higher-weight server is available.
Random	Distributes connections randomly among servers.
Source Tracking	Routes all connections from the same client IP to the same server (best-effort).

-T | --top option: restricts balancing to servers with the highest weight.

Runtime Management

GLB can be managed at runtime via:

• FIFO file

• Control socket (-c <addr:port>)

Commands

Command	Example	Description
Add/Modify server	echo "192.168.0.1:3307:5" | nc 127.0.0.1 4444	Add backend with weight 5
Drain server	echo "192.168.0.1:3307:0" | nc 127.0.0.1 4444	Stop new connections, keep existing
Delete server	echo "192.168.0.1:3307:-1" | nc 127.0.0.1 4444	Remove backend and close active connections
Get routing table	echo "getinfo" | nc 127.0.0.1 4444	Show backends, weight, usage, connections
Get stats	echo "getstat" | nc 127.0.0.1 4444	Show raw performance counters

Performance Statistics

Example:

echo "getstat" | nc -q 1 127.0.0.1 4444
in: 6930 out: 102728 recv: 109658 / 45 send: 109658 / 45 conns: 0 / 4 poll: 45 / 0 / 45 elapsed: 1.03428

Field	Description
in / out	Bytes received/sent via client interface
recv / send	Bytes passed and number of recv()/send() calls
conns	Created / concurrent connections
poll	Read-ready / write-ready / total poll calls
elapsed	Time since last report (seconds)

Watchdog

The watchdog module performs asynchronous health checks beyond simple TCP reachability.

Enable with:

glbd -w exec:"mysql.sh -utest -ptestpass" -t 2 3306 192.168.0.1 192.168.0.2

• Runs mysql.sh with host:port as first argument.

• Exit code 0 = healthy, non-zero = failure.

• Use -i to set check interval.

• With Galera, -D|--discover enables auto-discovery of nodes.

libglb (Shared Library)

libglb enables transparent load balancing by intercepting the connect() system call.

Basic Example

export LD_PRELOAD=/path/to/libglb.so
export GLB_OPTIONS="--random 3306 192.168.0.1 192.168.0.2 192.168.0.3"

mysql -uroot -p -h127.0.0.1 -P3306

Environment Variables

Variable	Description
GLB_WATCHDOG	Same as --watchdog option
GLB_TARGETS	Comma-separated list of backends (H:P:W)
GLB_BIND	Local bind address for intercepted connections
GLB_POLICY	Balancing policy (single, random, source)
GLB_CONTROL	Control socket for runtime commands

Operational Limits

• Limited by system open files (ulimit -n)

• With default 1024 → ~493 connections

• With 4096 (typical unprivileged user) → ~2029 connections

• Adjust in /etc/security/limits.conf if needed

See Also

• MariaDB MaxScale – recommended modern proxy

• Codership GLB on GitHub

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