A scalable MQTT broker written in erlang
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== Fubar ==
An MQTT message broker written in erlang targeted to support internet scale

== Getting Started ==
1. Getting dependencies and building
	$ make deps
	$ make
2. Starting a broker in interactive mode
	$ make test
3. Testing
	3.1. Starting a node for client
		$ make client
	3.2. Connecting clients (in the client shell)
		1> C1 = mqtt_client:start([{client_id, <<"c1">>}]).
		2> C2 = mqtt_client:start([{client_id, <<"c2">>}]).
	3.3. Subscribing and publishing messages
		3> C1 ! mqtt:subscribe([{topics, [<<"t1">>]}]).
		4> C2 ! mqtt:publish([{topic, <<"t1">>}, {payload, <<"hello!">>}]).
	3.4. Direct messaging
		This is an extra feature not originally stated in MQTT specification.
		One client may use the other client's client id as a topic name to
		send a message directly to the client.
		5> C2 ! mqtt:publish([{topic, <<"c1">>}, {payload, <<"world!">>}]).
4. Shutting down the broker gracefully.
	(fubar@host)1> fubar:stop().
	(fubar@host)2> q().

== More Features ==
1. Adding a new broker node to existing broker cluster
	$ make test master=name@host
	Note) If you want to start more than one broker node in a computer,
	You have to use different node name and listen port as:
	$ make test master=name@host node=other mqtt_port=1884
2. Using account control
	Uncomment {auth, mqtt_account} in src/fubar.app.src to enable auth.
	Then, call mqtt_account:update/2 as:
	(fubar@host)1> mqtt_account:update(<<"romeo">>, <<"1234">>).
3. More parameters for a client
	Full list of client parameters are:
	1> C3 = mqtt_client:start([{hostname, "localhost"},
	                           {port, 1884},
	                           {username, <<"romeo">>},
	                           {password, <<"1234">>},
	                           {client_id, <<"c1">>},
	                           {keep_alive, 60},
	                           {will_topic, <<"will">>},
	                           {will_message, <<"bye-bye">>},
	                           {will_qos, at_least_once},
	                           socket_options, [...]]).
	Refer inet:setopts/2 for socket_options.
4. Starting a broker in daemon mode
	Use 'run' instead of 'test'.
	$ make run
	Note) You may not start more than one daemon in a machine.

5. Getting a daemon shell
	$ make debug
	Note) The debug shell is closely bound with the daemon.  If you exit from
	the debug shell in a normal way, the daemon will stop.  Use CTRL-D to stop
6. Broker state is preserved
	The broker restores all the state -- accounts, topics and subscriptions -
	on restart.  To clear this state, do:
	$ make reset
7. Dumping logs to text files
	SASL logs can be taken as:
	$ make dump
	SASL logs show events happened in the start-up process and events not dealt
	with by the application.
	Application logs can be taken from the shell as:
	(fubar@host)1> fubar_log:dump(trace, "trace.log").
	Or you can dump all the logs by:
	(fubar@host)1> fubar_log:dump().
	Log classes are:
	- access	% network addresses of clients and disconnect events
	- packet	% bytes sent and received by the broker
	- protocol	% mqtt messages sent and received by the broker
	- resource	% long lasting resources such as sessions and topics
	- debug		% message put for debugging purpose
	- info		% irrelevant events taken but dropped
	- warning	% abnormal conditions that are not considered critical
	- error		% irrecoverable failures
	- trace		% fubar packets marked as trace
8. Log management
	Basically, two types of logs are used in fubar.  One is error_logger and the
	other is disk_log.  Most of the runtime events use disk_log and system
	start-up, shutdown events use error_logger.  error_logger is also called
	as SASL log.  The other difference is the fact that disk_log supports
	distributed logging but SASL log doesn't, which means that you can read
	all the disk_logs created in many nodes in one place but you have to go
	to each node to read SASL log.  Also, you can open/close/redirect disk_log
	at runtime.  Refer fubar_log:open/1, close/1, out/1, out/2 for more info.
	Log configuration stored in src/fubar.app.src controls both logs.
	~         {fubar_log, [{dir, "priv/log"},
	~                      {max_bytes, 10485760},
	~                      {max_files, 10},
	~                      {classes, [{trace, standard_io}, {warning, "fubar"}]}
	~                     ]},
	- dir		% Log files are left under <dir>/<node> usually "priv/log/fubar"
	- max_bytes	% Maximum individual log file size per class
	- max_files	% Maximum number of rolling log files per class
	- classes	% Initial disk_log classes to open
	Classes take {Class, Redirect} as values.  Class is one of the log classes
	listed in section 7.  Redirect is one of none, standard_io or "prefix".
	The meaning of the redirect is as follows.
	- none			% No redirect.  Logs are left in the binary files only.
	- standard_io	% Redirect to tty.
	- "prefix"		% Redirect to daily log files with the prefix.
	          		% e.g, "prefix_2012-12-29.log.1"
	As noted before, disk_log is distributed log.  Common practice to use
	distributed log in production is to use one node for central log consumer
	and set all the other nodes as log producer.  To configure your system like
	this, start a node with 'make run mqtt=undefined' command from a computer.
	Then you have a node 'fubar@host1' without a listener.  Now start other
	nodes with 'make run master=fubar@host1' command from other computers.  You
	may turn all the log classes off in all the other nodes and control in only
	one place, the monitor node.
	You will find following files under the log directory.
	- 1, 2,..., index		% SASL logs, binary rolling files.
	- access.*,...			% disk_logs for each class, binary rolling files.
	- run_erl.log			% Broker start-up linux command (production only).
	- erlang.log.*			% Erlang shell input/output history (production only).
	- *_YYYY-MM-DD.log.*	% Daily logs, text files without size limit.
	If you have daily logs in your log directory, you have to delete them
	regularly.  They are produced if you redirect any disk_log to file by
	setting {Class, "prefix"} in src/fubar.app.src or by calling
	fubar_log:out(Class, "prefix").

9. SSL support
	9.1. Prepare a certificate authority
		$ cd priv/ssl/ca
		$ mkdir certs private
		$ chmod 700 private
		$ echo 01 > serial
		$ touch index.txt
		$ openssl req -x509 -config openssl.cnf -newkey rsa:2048 -days 365 \
			-out cacert.pem -outform PEM -subj /CN=fubar_ca/ -nodes
		$ openssl x509 -in cacert.pem -out cacert.cer -outform DER
	9.2. Create a server certificate
		$ openssl genrsa -out ../key.pem 2048
		$ openssl req -new -key ../key.pem -out ../req.pem -outform PEM \
			-subj /CN=SomeHostName/O=YourOrganizationName/ -nodes
		$ openssl ca -config openssl.cnf -in ../req.pem -out ../cert.pem
			-notext -batch -extensions server_ca_extensions
		$ openssl pkcs12 -export -in ../cert.pem -out ../keycert.p12 \
			-inkey ../key.pem -passout pass:YourPassword
		The processes in 9.1 and 9.2 are stored in batch script
		priv/ssl/ca/new-certs.sh.  So you can just,
		$ cd priv/ssl/ca
		$ ./new-certs.sh
	9.3. Testing
		Use mqtts_port command line parameter to start an SSL listener when
		starting the broker.
		$ cd ../../..
		$ make test mqtts_port=8883
		Test basic connection with openssl s_client.
		$ openssl s_client -connect localhost:8883
		If it succeeds, use {transport, ranch_ssl} option on the client side.
		$ make client
		1> ssl:start().
		2> mqtt_client:start([{port, 8883},{transport, ranch_ssl},
			{client_id, <<"ssltest">>}]).

10. Benchmarking
	You can simulate many client connections with a computer.
	First, start a client shell.
	$ make client
	mqtt_client module provides batch functions, batch_start/2,3,
	batch_restart/0,1 and batch_stop/0.  Prepare a list of client id.
	1> Id = [list_to_binary(io_lib:format("~4..0B", [N])) ||
		N <- lists:seq(1, 1000)].
	Now you can use the list to call batch_start/2,3 as:
	2> mqtt_client:batch_start(Id, [{host, "broker addr"}, clean_session]).
	It may take some time to complete the batch start operation.
	You should be able to connect more than 50k clients from a computer.
	But of course you need to do proper kernel tuning and ulimit setting to
	do that.
	Start another client for probing.  We'll use this client later to
	generate load.
	3> Probe = mqtt_client:start([{host, "broker addr"},
		{client_id, <<"probe">>}, clean_session]).
	Now, we are ready to generate load.  Let's try direct messaging.
	4> Worker = mqtt_probe:start(Probe, Id, <<"...">>, 0).
	You should find endless messages printed by the batch clients.
	The above command spawns a Worker that publishes a message <<"...">> to one
	of the Id list every 0 millisecond using the client Probe.  You may want to
	monitor the broker's cpu/memory/io performance during this benchmark.  Use
	top or sar in that case.
	You can stop the worker any time.
	5> mqtt_probe:stop(Worker).
	Let's try another type of load now.  Make all the clients subscribe to a
	common topic.
	6> [Pid ! mqtt:subscribe([{topics,<<"t1">>}]) ||
		{_, Pid} <- mqtt_client_sup:running()].
	Then, use the probe to publish messages to the common topic periodically.
	7> f(Worker).
	8> Worker = mqtt_probe:start(Probe, <<"t1">>, <<"...">>, 1000).
	And so it goes.
== Configurations ==
Initial broker configuration is read from ebin/fubar.app which is compiled
from src/fubar.app.src.  You have to edit src/fubar.app.src to make your
configuration applied whenever you restart the broker.  Or you can call
fubar:settings/2 to apply changes while the broker is running.

(fubar@host)1> fubar:settings(mqtt_protocol, {max_packet_size, 8192}).

The above sample shows changing maximum MQTT packet size to 8kB.  This change
affects all the clients connection from this point on.  Note that some change
applies immediately but others require further intervention.

Refer src/fubar.app.src for details.