A presentation I made for the "Pervasive Systems" course of the "Master of Science in Engineering in Computer Science" at Sapienza Università di Roma (Sapienza University of Rome) A.Y. 2017/2018

1. M Q T T B R O K E R
Adriano Pimpini
Presentation for the Pervasive Systems course A.Y. 2017/18https://vernemq.com/

2. WHAT IS VERNEMQ?
VerneMQ is a high-performance, distributed MQTT broker,
which aims to provide high availability and scalability.
It is based on Erlang, and this enables VerneMQ to scale
horizontally and vertically by fully utilizing multicore
architectures.

3. MQTT – A QUICK RECAP
Publish/subscribe messaging protocol
For constrained devices in low-bandwidth, high-latency or unreliable networks
Built on top of TCP/IP
Quality of Service levels:
• QoS 0: At most once (Fire and forget)
• QoS 1: At least once
• QoS 2: Exactly once

4. PUBLISH/SUBSCRIBE ARCHITECTURE
GENERIC MQTT NETWORK WITH VERNEMQ

5. SETTING UP VERNEMQ
Download VerneMQ binaries or clone from git repository and build
Know where vernemq is
Get configuring!
git://github.com/erlio/vernemq
.git
$ whereis
vernemq

6. SOME VMQ FEATURES
• File based Authentication & Authorization
• Database based Authentication and Authorization
• Listeners
• Multiple Sessions per ClientId
• Session Balancing
• Cluster Support

7. FILE BASED AUTHENTICATION
/etc/vernemq/vernemq.conf is the main configuration file for VerneMQ
vmq_passwd.password_file =
/etc/vernemq/vmq.passwd
will be our password file
Add an entry to the password file:
We are then prompted to enter the
password of the user. It will be encrypted and stored in the format
usrname:password
$ vmq-passwd.password –a passwfile
username
pippo:$6$FUUkqxsyQ1HTpWvu$92sr3KrC/w2sHS[…]19mMB4U7MJvUGSMfxHQA
==
allow_anonymous=off Anonymous user access control
We want to accept only configured users. We set it on, and force
authentication

8. vmq_acl_file =
/etc/vernemq/vmq.acl
will be our access control list file
FILE BASED AUTHORIZATION
We need to set the content of vmq.acl manually.
user pippo
[topic|pattern] [|read|write]
$topic
This is the pattern for defining
user pippo’s access privileges
topic read system/log
topic s01/info
pattern write %u/#
Means the user can read the system/log
topic
User can read/write to s01/info topic
User can write to all topics under its
username
If no user is specified, the policy applies to everyone, even anonymous
users

9. LISTENERS
Listeners specify on which IP address and port VerneMQ should accept new incoming
connections.
listener.max_connections = 10000
listener.nr_of_acceptors = 10
Maximum concurrent connections per listener
Acceptors processes that accept new
connections
listener.x.name = IP:port Syntax for listener binding
listener.tcp.default = 10.0.0.130:1883
Bind the tcp «default» listener to IP
10.0.0.130 on port 1883:

10. SESSIONS AND BALANCING
VerneMQ supports multiple sessions per client ID
(note: ClientID ≠ username!)
This means that there will be many instances consuming messages directed to that
client.
VerneMQ can balance the load between instances with the same client ID and
subscription so that the consumer can work faster.
Command that activates the balanced delivery on broker
node
allow_multiple_sessions = on
queue_deliver_mode =
balance

11. STARTING A NODE
To start a node
To verify that a node is running
To stop a node
$ vernemq start
$ vernemq ping
>pong
$ vernemq stop

12. CLUSTERING
Clustering in VerneMQ is rather easy. All you need to do is:
Set a private cookie in the configuration file. It is the same on every cluster node.
Set a name for every node.
Define the behaviour in case of Netsplit (i.e. node failure)
Join a cluster!
Or, when you want to leave a cluster
distributed_cookie= vmq
nodename = VMQ@10.0.0.130
allow_register_during_netsplit = on/off
allow_publish_during_netsplit = on/off
allow_subscribe_during_netsplit = on/off
allow_unsubscribe_during_netsplit = on/off
$ vmq-admin cluster join discovery-node=<OtherClusterNode>
$ vmq-admin cluster leave node=<LeavingNode>

13. LET’S TALK
ABOUT TESTING

14. THE SETUP
Broker cluster nodes:
• 3 Cloned Lubuntu 16.04 Virtual Machines
• 1GB RAM
• 1 CPU core @1.6GHz (Physical CPU: Intel Core i5 8250U)
• Connected to network through wi-fi & bridged network adapter mode
Clients:
• 1 Lubuntu 16.04 Virtual Machine
• 15 GB RAM
• 8 CPU cores @3.4GHz (Physical CPU: Intel Core i7 3770)
• Connected to network through ethernet & bridged network adapter mode
• Language: Python, Library: paho.mqtt

15. STRESS PROCESS & MEASUREMENTS
• Tested both in 3 node cluster, and single node
• Client machine spawns clients, either publishers or subscribers, one thread for each.
• Publishers publish on one of 4 random topics
• Subscribers subscribe to one of 4 random topics
• Publishers publish 5 messages per second, with 64B payload (timestamp + padding)
• Each publisher posts 100 messages and then exits
• Each subscriber waits for 200 messages and then exits
• Upon connecting or receiving a message, clients calculate the delay
• QoS in [0,1,2]; Publisher count in [20,50,100,200]; Subscriber count in [20,50,100,200]

16. 20-50 PUBLISHERS
3 Node cluster Single node
all times are in milliseconds

17. > 100 PUBLISHERS
3 Node cluster Single node
all times are in milliseconds

18. THANKS FOR YOUR ATTENTION
https://www.linkedin.com/in/adriano-pimpini/
https://github.com/BathtubRacer
Adriano Pimpini
Presentation for the Pervasive Systems course A.Y. 2017/18