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OTP in Server Farms

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Hal Snyder
hal@vailsys.com

Michael Bruening
mike@vailsys.com

Martin Logan
martin@vailsys.com

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what this talk is about


	why use Erlang and OTP

	features of the present OTP platform

	unsolved problems

	conclusions

	fun projects

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why use Erlang and OTP


	Vail Systems

	typical resources on our network

	why OTP appeals to us

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Vail Systems


	computer telephony applications service provider

	voice over IP (SIP)

	custom IVR and VoiceXML

	2 sites, 3 million calls / day


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typical resources on our network


	proxy for remote database queries (SQL and other)

	outbound call routing

	telephony resource allocation

	call detail monitoring and spooling

	VoiceXML initial page selection

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why OTP appeals to us

	distributed, protocol is written and debugged

	rapid development

	concurrent programming model without threads

	mnesia

	behaviours

	administrivia

	change in mindset

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features of the present platform

	build system

	configurable parameters

	resource discovery

	logging

	monitoring

	interaction with non-OTP systems

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build system

	CVS

	release contains all modules

	development and production environments

	boilerplate for .app and .rel

	support *BSD, Linux, Solaris

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configurable parameters

now less painful than the dentist!

	static configuration = pain
		config files
		environment variables
		command line arguments
		restart servers on every config change

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	dynamic config - central or distributed & replicated = mnesia
		all that's needed is static bootstrap info
		single & unified data format
		optionally notify clients of changes automatically
		one simple web interface to config database


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resource discovery


	network must know all producers and consumers of each resource

	automatic registration and deregistration of hosts

	two tables: produce & consume. "I have" & "I want"

	our "chicken-and-egg" problem "resolved" by DNS SRV

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logging


	purpose is diagnostic

	like syslog, one line of cleartext per record

	file rotation compatible with "smart" tail program
		name of most recent log file does not change

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		vl_syslog_h.erl

		vl_elwrap_h.erl

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monitoring

	is subsystem available?

	how much work is it doing?

	interface with non-OTP systems i.e RRD

	SNMP too bulky

	use HTTP(inets, yaws) to export useful information

	RRD for trends

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interaction with non-OTP systems

	C++, custom TCP - SIP IVR API

	custom UDP - simple non-SQL queries

	HTTP - configuration and stats

	SMTP - mail out alerts

	ODBCserver - Oracle proxy

	filesystem - OTP writes some log files

	jinterface (new) - 3rd party Java apps

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unsolved problems


	resume mnesia replication after network partition

	dynamic application mix

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conclusions


	shallow learning curve

	easily adapted to server farm environment 
		build system
		interfaces to rest of the platform
		mnesia replication planning
		resource discovery

	reusable code. when on its best "behaviour" beats OO!

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wishlist

	dynamic application mix (OTP emulates OS)

	more flexible mnesia recovery from partitioning

	command line interface (like inets for telnet)

	replicated history of counters (RRD on mnesia)

	spread the word!

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fun projects

when we get the time ...

	SIP agents

	LDAP on mnesia

	mnesia.pm

	bring back IPv6 OTP transport

	i18n