dynlbd.py

simple DNS load balancer written in python.

configuration

The program read its configuration from a YAML configuration file /etc/dynlbd.conf

the configuration structure is the following:

option: value
FQDNpoolname:
   IPaddress:
      - module

FQDNpoolname is a valid DNS FQDN which identifies a series of A records for that specific pool, for example:

login.mydomain.org has two A records in the DNS:

login.mydomain.org has address 192.168.122.151
login.mydomain.org has address 192.168.122.150

we define those in the configuration file:

login.mydomain.org:
   192.168.122.150:
       - all
   192.168.122.151:
       - all

the program will check for the hosts in the config file to be in a healthy status. All the hosts are running Prometheus node_exporter and checks are made by inquiring the hosts node_Exporter directly. If they aren't healthy, the specific IP address belonging to the unhealthy host will be removed by the DNS using a rfc2136 query.

The same host will be added later to the DNS record A pool whenever in healthy status

The available modules for health check are:

- cpu 	// check for cpu usage
- mem   // check for memory usage
- load  // check for load averages
- all   // all of the above modules
- net   // check for network usage

cpu

if the cpu usage is more than 90% the host is marked as BAD

mem

if the free memory percent is lower than 5% the host is marked as BAD

load

if one minute load average is greater then the number of cores on the system the host is marked as BAD

net

if RX or TX bandwidth his above 80% the node is marked as BAD

the "net" module tag needs to reference the interface name stats to be gathered on the remote host:

login.mydomain.org:
   192.168.122.150:
       - net.enp0f0s0

The ICMP ping module is always run by default and only if the host answers to ICMP echo queries it will be probed for subsequent health checks.

To run just a ICMP probe do not add any module option. For example:

login.mydomain.org:
   192.168.122.150:
   192.168.122.151:
       - all

host 192.168.122.150 will just have a ICMP probe.

IPv6 is supported, in that case for Link Local IPv6 a "%" will need to be appended to the IPv6 address. For example:

bastion.mydomain.org:
   fe80::2245:fa:febc:2008%virbr0:
       - cpu
   192.168.122.180:
       - all

Usage

usage: dynlbd.py [-h] [-cf CONFIG_FILE] [-pm PING_METHOD]
                 [-d | -f | -k KUBELOG]

./dynlbd.py

optional arguments:
  -h, --help            show this help message and exit
  -cf CONFIG_FILE, --config-file CONFIG_FILE
  -pm PING_METHOD, --ping-method PING_METHOD
                        OS|internal
  -d, --Daemon          run as a Daemon
  -f, --foreground      run in foreground, NO Daemon
  -k KUBELOG, --kubelog KUBELOG
                        log file path for kubernetes mode

Build

several python modules need to be installed with "pip" prior to run dynlbd.py

a custom module to create sysV shmem is provided as C code. to build the so library:

gcc -fPIC -shared -o shm.so shm.c

Testing

dynlbd.py has been tested runnning python3.9