1. Making Fault-Tolerance a Reality `
Erlang and the OTP
Making Fault-Tolerance a Reality `

2. Before We Begin > dialyzer --build_plt --apps stdlib kernel erts
Slides and code are at git://github.com/bernardd/OTPworkshop.git

3. Who on Earth are you? ShoreTel Sky http://shoretelsky.com
“Enterprise Grade” Hosted VoIP

4. Let's Write a Chat Server
Processes:
Main Server
Socket Listener
Client Processes

5. The OTP Supervision Trees applications gen_server gen_fsm gen_event
It's what makes Erlang's promise of fault tolerance a reality

6. application Coarse grained building blocks Start and stop individually
Reusable
e.g.: Mnesia, SNMP, Crypto

7. gen_server Basic long lived “server” process
Responds to synchronous and asynchronous requests

8. gen_fsm Framework for finite state machine process
In reality it's pretty limited and not widely used

9. gen_event Subscribe-notify system
The gen_event module is the subscriber

10. supervisor Watches processes Restarts crashed ones (if needed)
Restart strategies:
one_for_one
one_for_all
rest_for_one
simple_one_for_one

11. Supervision Trees Our OTP-ised chat server:
Main supervisor (one-for-one)
Client supervisor (simple-one -for-one)
Chat server
Connection listener
Clients
…....

12. Supervisor Specification
{ok, {{
one_for_one, % Strategy
4, % Max retries
% Max time },
[ % Children {
client_sup, % ID
{Module, Function, [ArgList]}, % Start spec MFA
permanent, % Restart type
1000, % Shutdown timeout
worker, % Child type
[Module] % Child modules
... % More children here
]}}.

13. Let's Crash Some Processes!
observer:start()

14. gen_event gen_event:start_link({local, EvtMgr})
gen_event:add_handler(EvtMgr, HandlerModule, Args)

15. Hot Code Loading
It's so cool

16. Dialyzer

17. Questions?

18. Thanks!
The End.