##Raft
A raft cluster contains several servers which allows the system to tolerate failure(for 5 servers, it will be 2). This template/pkg is implementing this algorithm. In this, one leader will be selected among the servers.
#Implementation Details -Key-Value + Raft + leveldb -On startup Key-Value Map will be constructed from Logs saved in leveldb
#Extension -if request comes to follower,redirecting it to leader. ------->completed
-use of zmq/http(redirect will be simpler) instead of relying on simple tcp client-server. ------->completed
-automate test for Key-Value. ------->completed.
#Dependencies:- LevelDB:- github.com/syndtr/goleveldb/leveldb ZMQ:- github.com/pebbe/zmq4
#Usage
go get github.com/mgkanani/cluster
go get github.com/mgkanani/raft
go install github.com/mgkanani/raft ->raft implementation code
go install github.com/mgkanani/raft/KeyValue ->KeyValue Server code
go install github.com/mgkanani/raft/KeyValue/client -> client for KeyValue.
go install github.com/mgkanani/raft/leveldb_check -> This is used in testing of KeyValue also.
go get github.com/mgkanani/raft/RaftMain
go install github.com/mgkanani/raft/RaftMain ->This is used in during testing of raft leader election code check.
go test github.com/mgkanani/raft
To test KeyValue go into KeyValue Directory and execute commands in below order.
go install
go test
./test_script.sh -> Output in all line must be same.
-Tests are performed on 3-different machines(From 7 servers 2,2,3 servers on respective machines) for testing the working of Raft.
-go test performs testing of raft by killing each process one by one after every 15-sec. This will be performed 3 times.
-2 clients sending 200 requests sending simultaneously, 7-servers were running on single host. Leader was killed manually[Cntr+c] when it reached to only 3 servers, there was no leader, then one by one server started. Then Leveldb data checked and found identical.
to see all logs and what is happening during execution,
modify RaftMain/main.go file,line-37 update to true instead of false
modify raft_test.go,line-19, do same as above.
modify KeyValue/KeyValue_server.go line-25/26, do same as above.
to change data which sent by client and to change the KeyValue sever's ipaddr:port modify:-
KeyValue/client/client.go file, line num 25 for change data.
KeyValue/client/client.go file, line num 30 for ipaddr:port.
What is tested during testing or how testing is performed on servers for leader election(what is logic
inside raft_test.go):-
-All servers are started
-at every 5-sec 1-server will go down
-all servers exactly 3-times goes down during testing.
-at every 1.5sec who is Leader is checked and checked whether there are more than one Leader.
If there is more than one Leader is found , then test will return panic.
##Documentation reference:-
###Modify config.json
-To add more servers with different port and pids.
-Pids must be in strictly order means 1,2,3,4 but not 1,2,4,7.
-The order 1,4,3,2 will work perfectly.
###Modify KeyValue/KeyValue.json -To add more servers with different port and pids.
-Pids must be in strictly order means 1,2,3,4 but not 1,2,4,7.
-The order 1,4,3,2 will work perfectly.
-make sure this file is used by front-end KeyValue servers. This server parameters is used by client to connect to server.
###Modifying raft_test.go -Make sure that "total_servers" variable at line 17in this file must match with total numbers of servers in config.json file.
#Default configurations:-
Total Servers :- 7
ipaddr:127.0.0.1
ports :-12345,12346,12347,12348,12349,... ,12351
Pids:-1,2,3,4,5,6,7
ports :-45001,45002,...,45007 ->This is for Key-value servers.
#Experiments:-
-Tested on multiple virtual machines during leader election.
-Tested on network partition problem.
-Latest manual test is performed for 2-client simultaneously sending 200 requests and 7-servers were there.
One by one leader is killed, everytime new leader elected in less than 1 or 2 sec till the numbers of healthy servers was 4.
After some time one by one server started and at last their leveldb content were checked and they found identical.
#References for basics of ZeroMQ and implemention
use of offline documentation of go-language that is using below commands :-
to find path of offline documentation:- godoc dfdsgdg this package will not available and it will tell the path of godoc is looking for.
to find available packages:- ls /usr/lib/go/src/pkg , now observe packages and find approapriate pkg that is math/rand.
now use:-godoc math/rand
[https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf]( -- for reading raft paper as).
http://stackoverflow.com/questions/8270816/converting-go-struct-to-json
[https://groups.google.com/forum/#!msg/golang-dev/oZdV_ISjobo/N-vfSnrcqhcJ]
[http://golang.org/pkg/time/#Timer.Stop]
[http://stackoverflow.com/questions/13812121/how-to-clear-a-map-in-go]
[http://stackoverflow.com/questions/1841443/iterating-over-all-the-keys-of-a-golang-map]
[http://stackoverflow.com/questions/19965795/go-golang-write-log-to-file]
[http://www.sunzhongkui.me/rpc-communication-in-go-language/]
[http://play.golang.org/p/5LIA41Iqfp] -> to discard all log data ( this is done only for raft_test.go file.)
[http://stackoverflow.com/questions/21532113/golang-converting-string-to-int64]
[https://github.com/golang-samples/http] -> post directory
#Mistakes(very silly but consumes much time) during coding which takes hours to find and resolve.
Making Request and Reply's data as private and using marshal and Unmarshal function which returns null data.
During coding, made mistake while copying the same logic reside in same file and only some of part need to modify. These type of logical bug for which we are certainly sure that we have made correctly are found.