We set up a VerneMQ 3 nodes cluster (https://vernemq.com/docs/clustering/).
The problem is I didn’t find any example on how to connect the clients to the whole cluster.
E.g. for a single VerneMQ instance the client connection (in python) is:
client.connect("xxx.xxx.xxx.xxx", 1883, 60)
where "xxx.xxx.xxx.xxx" is the address of the single instance.
In case of cluster is there a way to specify the address of the whole cluster, instead of pointing a single node?
With my client written using Paho MQTT client library, I ended up in using the following extension of Client class:
import random
from paho.mqtt.client import *
class ClusterClient(Client):
"""A subclass of paho.mqtt.Client that supports connecting to a cluster of
mqtt brokers. connect() and connect_async() additionally accept a list
of hostnames or host/port tuples:
connect("host1")
connect(["host1", "host2", "host3"]) # use default port 1883
connect(["host1", ("host2", 8883), ("host3", 8883)])
Hosts to connect to are chosen randomly. If a host disappears the client
automatically connects to another host from the list.
"""
def __init__(self, client_id="", clean_session=True, userdata=None,
protocol=MQTTv311, transport="tcp"):
super().__init__(client_id, clean_session, userdata, protocol, transport)
self._hosts = []
def connect_async(self, host, port=1883, keepalive=60, bind_address=""):
if isinstance(host, (list, tuple)):
self._hosts = [(t, 1883) if isinstance(t, str) else t for t in host]
else:
self._hosts = [(host, port)]
for host, port in self._hosts:
if host is None or len(host) == 0:
raise ValueError('Invalid host.')
if port <= 0:
raise ValueError('Invalid port number.')
host, port = random.choice(self._hosts)
super().connect_async(host, port, keepalive, bind_address)
def reconnect(self):
hosts = self._hosts[:]
random.shuffle(hosts)
while True:
self._host, self._port = hosts.pop(0)
try:
return super().reconnect()
except socket.error:
if not hosts:
raise
There is no such thing as the "specific address of the whole cluster". (for VerneMQ and for any other clustered server software).
If you need a single point of contact, you need a load balancer in front of the cluster. You can then use different load balancing strategies.
VerneMQ works well with HAProxy for instance and supports the proxy protocol.
Hope this helps.
