routing - Akka messaging mechanisms by example -

i have fair amount of apache camel (routing/mediation/orchestation engine; lightweight esb) experience , racking brain trying understand difference between akka:

• dispatchers (dispatcher, pinneddispatcher, callingthreaddispatcher)
• routers
• pools
• groups
• event buses

according docs:

dispatchers are:

...is makes akka actors “tick”, engine of machine speak.

but doesn't explain dispatcher or it's relationship actor is.

routers are:

messages can sent via router efficiently route them destination actors, known routees. router can used inside or outside of actor, , can manage routees yourselves or use self contained router actor configuration capabilities. sounds awful lot dispatcher.

pools are:

[a type of] router [that] creates routees child actors , removes them router if terminate.

groups are:

[a type of] actor [where routees] created externally router , router sends messages specified path using actor selection, without watching termination.

event buses are:

...a way send messages groups of actors

this sounds dispatchers , routers.

so main concerns are:

• what difference between dispatchers, routers , event buses, , when use each?
• when use pool vs group?

a dispatcher thread-pool. akka uses dispatcher multiple things (like enqueueing messages in right mailbox or pick message actor mailbox , process it). every time 1 of these actions need performed thread thread-pool selected , used it. akka comes default default-dispatcher config can find here in reference.conf searching default-dispatcher. using default-dispatcher can define different dispatcher ensure have reserved thread-pool other purposes (for example netty threads when using akka-remote or akka-cluster).

a router in akka actor uses kind of routing logic route messages list of routees. there many types of router depending on logic: broadcast, balancing, roundrobin... can find of them in akka docs. routees of router can pool or group. 1 of popular use cases of routers vertically scale app means maximize use of cpu available in system (using multiple threads @ same time).

a pool means routees being created on-demand given type. example may want randompool of myfancyactor 3 instances. akka create 3 actors of myfancyactor , fourth 1 actual router. every time router actor gets message forwarding message 1 of 3 myfancyactor actors. pool takes care of restarting actors , watch lifecycle ensure have n number of instances running.

a group means routees being created before defining router. once defining router need pass list of routees actor created. group not monitor lifecycle of actors , need yourself.

event buses channels can subscribe particular type of message actor. if there message of particular type, actor it. used akka internals subscribing deadletters when message unable reach destination or events regarding formation of cluster (in akka-cluster). use aware of events happening in actorsystem.