Introduction to egearmand an Erlang implementation of the Gearman server

1. egearmand: an erlang
gearman daemon

2. • OTP compliant distributed application
• Full support of the Gearman binary
protocol
• Support of the Gearman administrative
protocol
• Focus on reliability and scalability

3. Concurrency
• Each erlang process can be executed
concurrently in any available core
• Concurrent processing of requests

4. supervisor
WorkersReg FunctionsReg JobsQueue Connections
WorkerProx
WorkerProx
WorkerProx WorkerProx
WorkerProx
WorkerProx
WorkerProx
WorkerProx
yy WorkerProx
WorkerProx
yy
yy
WorkerProxy yy
ClientProxy
y y

5. Job Queues
• Queues stored in Erlang’s distributed
database Mnesia
• Optional persistence support
• Replication: read nodes (in-memory) and
write nodes (fallback, disk copies) can be
declared

6. configuration.erl
%% @doc
%% Specifies if the Gearman queues should be
%% persistent between servers restarts.
-spec(persistent_queues() -> true | false) .
persistent_queues() -> false .
%% @doc
%% If using persitent job queues, nodes where
%% to store disc copies.
-spec(backup_gearmand_nodes() -> [node()]) .
backup_gearmand_nodes() ->
[node()] .

7. mnesia (disc copy)
egearmand
mnesia (memory)
Erlang node
Erlang node
mnesia (disc copy)
Erlang node

8. mnesia (disc copy)
Erlang node
mnesia (disc copy)
Erlang node

9. egearmand
mnesia (disc copy)
Erlang node
mnesia (disc copy)
Erlang node

10. Clustering
• A set of nodes running egearmand acting as
a single gearman server

11. Clustering
egearmand (slave) gearman worker
egearmand (master)
Erlang node
Erlang node
egearmand (slave) gearman client
Erlang node

12. Failover
• worker failover
• erlang process failover
• erlang node failover

13. Worker Failover
• tasks being executed can be re-scheduled in
the queue
• specified in configuration

14. configuration.erl
%% @doc
%% What to do if a worker fails while executing a task.
%% If the value is set to reeschedule the task will be
%% queued again.
%% If the value is set to none, it will be discarded.
-spec(on_worker_failure() -> reeschedule | none) .
on_worker_failure() ->
reeschedule .

15. Erlang Processes
Failover
• OTP application
• Supervisor restarts failing processes

16. Erlang Nodes Failover
• Distributed OTP application
• Handles node crashes
• Application re-started in another node
(take over)
• Slave nodes not affected

17. Extensions
• Extensions support
• Bridge between erlang processes and
gearman worker/clients
• Extensions hooked in the request
dispatcher
• Associated to certain function names
• RabbitMQ extension included

18. /egearmand/rabbitmq/declare
rabbitmq /egearmand/rabbitmq/publish
extension gearman client
rabbitmq egearmand
gearman worker
Erlang node /egearmand/rabbitmq/consume

19. rabbitmq_extension.erl
%% @doc
%% We state which messages are we interested to process
-spec(connection_hook_for(atom()) -> boolean()) .
connection_hook_for(Msg) ->
log:debug(["Checking hook for", Msg]),
case Msg of
{submit_job, ["/egearmand/rabbitmq/declare", _Unique, _Options]} -> true ;
{submit_job, ["/egearmand/rabbitmq/publish", _Unique, _Options]} -> true ;
{submit_job, ["/egearmand/rabbitmq/consume", _Unique, _Options]} -> true ;
_Other -> false
end .
%% @doc
%% We state which messages are we interested to process
-spec(entry_point(atom(), socket()) -> boolean()) .
entry_point(Msg, Socket) ->
log:debug(["Entry point of the extensions", Msg, Socket]),
case Msg of
{submit_job, ["/egearmand/rabbitmq/declare", _Unique, Options]} ->
process_queue_creation(Options, Socket) ;
{submit_job, ["/egearmand/rabbitmq/publish", _Unique, Options]} ->
process_queue_publish(Options, Socket) ;
{submit_job, ["/egearmand/rabbitmq/consume", _Unique, Options]} ->
process_queue_consume(Options, Socket) ;
_Other ->
false
end .

20. Gotchas
• Early stage of development
• Untested performance
• Local connections (process/node) lost in
the event of a failure restart
• Difficult configuration (needs recompiling)
• Not release or boot script

21. git clone git://github.com/antoniogarrote/egearmand-server.git