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Apache%20Cassandra%20is%20a%20distributed%20database%20management%20system%20designed%20to%20handle%20large%20amounts%20of%20data%20across%20many%20commodity%20servers%2C%20providing%20high%20availability%20with%20no%20single%20point%20of%20failure.%20Cassandra%20was%20developed%20at%20Facebook%20and%20released%20as%20an%20open-source%20project%20in%202008.%20It%20is%20now%20used%20by%20a%20number%20of%20organizations%2C%20including%20Netflix%2C%20eBay%2C%20and%20the%20U.S.%20Government.%0A%0AOne%20of%20the%20key%20features%20of%20Cassandra%20is%20its%20ability%20to%20scale%20horizontally%2C%20meaning%20that%20it%20can%20easily%20handle%20large%20amounts%20of%20data%20by%20simply%20adding%20more%20commodity%20servers%20to%20the%20cluster.%20This%20is%20made%20possible%20by%20Cassandra's%20distributed%20architecture%2C%20which%20allows%20it%20to%20distribute%20data%20across%20the%20cluster%20and%20automatically%20replicate%20it%20for%20fault%20tolerance.%0A%0AAnother%20important%20feature%20of%20Cassandra%20is%20its%20support%20for%20tunable%20consistency%2C%20which%20allows%20users%20to%20choose%20the%20level%20of%20consistency%20they%20need%20for%20their%20specific%20use%20case.%20This%20is%20useful%20because%20different%20applications%20may%20have%20different%20requirements%20for%20data%20consistency%2C%20and%20Cassandra%20allows%20users%20to%20fine-tune%20the%20consistency%20level%20to%20meet%20their%20needs.%0A%0AIn%20addition%20to%20its%20scalability%20and%20tunable%20consistency%2C%20Cassandra%20also%20offers%20strong%20security%20features%2C%20including%20support%20for%20encryption%20and%20authentication.%20It%20also%20has%20a%20robust%20query%20language%20called%20CQL%20(Cassandra%20Query%20Language)%20that%20is%20similar%20to%20SQL%20and%20allows%20users%20to%20easily%20retrieve%20and%20manipulate%20data%20in%20the%20database.%0A%0A%23%23%23%20Primary%20Key%0A%0AIn%20Cassandra%20primary%20key%20is%20consists%20of%20partition%20keys%20and%20clustering%20keys.%20In%20other%20words%20primary%20key%20is%20how%20you%20uniquely%20identifies%20a%20row.%0A%0AExample%2C%0A%60%60%60go%0Atype%20User%20struct%20%7B%0A%09Email%20string%0A%09Name%20string%0A%09City%20string%0A%7D%0A%60%60%60%0A%0A%60%60%60text%0APRIMARY%20KEY%20((City)%2C%20Email))%20WITH%20CLUSTERING%20ORDER%20BY%20(Email%20ASC)%0A%60%60%60%0A%0AIn%20above%20example%20%60City%60%20is%20partition%20key%20and%20%60Email%60%20is%20clustering%20key.%0A%0A**Partition%20Key**%0A%0APartition%20key%20is%20used%20to%20distribute%20data%20across%20the%20cluster.%0A%0A**Clustering%20Key**%0A%0AClustering%20key%20is%20used%20to%20sort%20data%20in%20a%20partition.%0A%0A%23%23%23%20Replication%0A%0AReplication%20factor%20in%20Cassandra%20is%20used%20to%20replicate%20data%20across%20the%20nodes%20of%20the%20cluster.%20The%20goal%20of%20data%20replication%20is%20ensuring%20high%20availability%20of%20the%20system%2C%20even%20if%20some%20node%20dies%20or%20faces%20network%20failures.%20There%20is%20a%20saying%2C%20In%20distributed%20systems%20whatever%20can%20go%20wrong%2C%20will%20go%20wrong.%20So%20you%20have%20to%20prepare%20for%20that.%0A%0A%23%23%23%20Partitioning%0A%0ABy%20partitioning%20you%20are%20splitting%20data%20across%20multiple%20servers.%20So%20over%20the%20time%20when%20the%20data%20will%20grow%2C%20you%20can%20add%20more%20servers%20to%20the%20cluster%20to%20scale%20the%20system%20and%20handle%20the%20growing%20data.%20Let's%20say%20you%20are%20handling%20terabytes%20of%20data%20then%20it%20will%20be%20difficult%20to%20handle%20them%20in%20a%20single%20server.%0A%0A!%5B%5D(https%3A%2F%2Fcdn.shopemaa.cloud%2F4f877f28-3e2a-47a4-a195-2689d1789ed3%2Fmedia%2F63b803ee-f8ba-4355-8ad5-81ea8217f93c-U2NyZWVuc2hvdCAyMDIzLTAxLTA4IGF0IDEuMDUuNDEgQU0%3D.png)%0A%0AIn%20above%20picture%20we%20have%20an%20example%20table%20with%20fields%20UserEmail%2C%20Name%20and%20City.%20In%20this%20example%20we%20are%20partitioning%20data%20based%20on%20City.%20So%20the%20hash%20function%20will%20generate%20a%20hashed%20key%20using%20the%20City%20value%20to%20map%20the%20data%20to%20a%20specific%20node%20within%20the%20cluster.%20For%20example%2C%20City%20A%20hashed%20to%2010%2C%20City%20B%20hashed%20to%2015%20and%20so%20on.%0A%0AIn%20the%20below%20picture%20we%20have%20a%20cluster%20of%204%20nodes.%20And%20each%20node%20handles%20a%20range%20of%20data.%20So%20based%20on%20our%20example%20data%20with%20hashed%20key%200-25%20will%20go%20to%20node%201.%20Hence%20City%20A%20and%20City%20B%20will%20go%20to%20node%201.%0A%0A!%5B%5D(https%3A%2F%2Fcdn.shopemaa.cloud%2F4f877f28-3e2a-47a4-a195-2689d1789ed3%2Fmedia%2Fcc5580b9-3504-412c-8021-4ff97355a68f-U2NyZWVuc2hvdCAyMDIzLTAxLTA4IGF0IDEuMzAuNDUgQU0%3D.png)%0A%0AIt%20is%20also%20important%20to%20consider%20if%20the%20hash%20function%20is%20generating%20an%20evenly%20distributed%20hashed%20key.%20Otherwise%20there%20is%20a%20chance%20that%20most%20of%20the%20data%20will%20go%20to%20some%20nodes%20and%20other%20nodes%20will%20have%20less%20data.%20So%20the%20data%20distribution%20won't%20be%20optimal.%0A%0A%23%23%23%20Consistency%0A%0AIn%20Cassandra%20you%20can%20configure%20the%20consistency%20level.%20Based%20on%20your%20requirements%20you%20can%20decide%20and%20configure%2C%20what%20kind%20of%20consistency%20you%20want.%20Also%20keep%20in%20mind%20that%20we%20achieve%20strong%20consistency%20by%20compromising%20performance.%0A%0AOverall%2C%20Apache%20Cassandra%20is%20a%20powerful%20and%20flexible%20distributed%20database%20management%20system%20that%20is%20well-suited%20for%20handling%20large%20amounts%20of%20data%20in%20a%20distributed%20environment.%20It%20is%20used%20by%20many%20organizations%20around%20the%20world%20and%20is%20a%20popular%20choice%20for%20applications%20that%20require%20high%20availability%20and%20strong%20security.%0A%0A**ScyllaDB**%20is%20a%20good%20alternative%20to%20Cassandra.%20ScyllaDB%20uses%20same%20CQL%20protocol%20as%20Cassandra.%20But%20if%20you%20are%20looking%20for%20a%20manged%20service%20then%20AWS%20DynamoDB%20is%20something%20to%20consider%20alone%20with%20ScyllaDB%20cloud.

Getting started with Apache Cassandra

What's%20up%20good%20people%20%3F%20Hope%20well.%0A%0AOk%2C%20Few%20days%20back%20was%20trying%20to%20setup%20MQTT%20cluster%20server%20and%20choose%20HAProxy%20to%20use%20as%20load%20balancer.%0A%0AThis%20is%20a%20short%20guide%20how%20I%20managed%20everything.%0A%0AI%20have%203%20server%20from%20digital%20ocean%20(vps%20service%20provider).%0A%0AAssume%20they%20are%20%3A%0A%0A1.%20lb.example.com%20(192.168.0.101)%0A2.%20node1.example.com%20(192.168.0.102)%0A3.%20node2.example.com%20(192.168.0.103)%0A%0Alb.example.com%20is%20load%20balancer%20where%20I%20setup%20HAProxy.%0A%0Anode1.example.com%20is%20first%20server%20of%20mqtt%20and%0A%0Anode2.example.com%20is%20second%20server%20of%20mqtt.%0A%0AI%20used%20emqttd%20as%20MQTT%20broker.%20%5BDownload%20link%5D(http%3A%2F%2Femqtt.io%2Fdownloads)%0A%0AAfter%20emqttd%20setup%20on%20node1%20and%20node2%20to%20enable%20clustering%20enter%20into%20node1.example.com%20change%20hostname%20to%0A%0A**node1.example.com**%0A%0Achange%20in%20**etc%2Femq.conf**%20as%20%3A%0A%0A%60%60%60bash%0Anode.name%20%3D%20emqttd%40node1.example.com%0A%60%60%60%0A%0ADo%20same%20for%20node2%20but%20here%20with%20node2.example.com%0A%0ANow%20from%20node1%20or%20node2%20execute%0A%0A%60%60%60bash%0Aemqttd_ctl%20cluster%20join%20emqttd%40node2.example.com%0A%23%20Assuming%20you%20are%20on%20node1%0A%60%60%60%0A%0Anow%20to%20check%20cluster%20status%20execute%2C%0A%0A%60%60%60bash%0Aemqttd_ctl%20cluster%20status%0A%60%60%60%0A%0AResult%20should%20be%2C%0A%0A%60%60%60bash%0A%5B%7Brunning_nodes%2C%5B'emqttd%40node1.example.com'%2C'emqttd%40node2.example.com'%5D%7D%5D%0A%60%60%60%0A%0ANow%20time%20to%20setup%20HAProxy%20for%20load%20balancing%2C%0A%0AEnter%20into%20**lb.example.com**%20and%0A%0AInstall%2C%0A%0A%60%60%60bash%0Asudo%20apt-get%20install%20haproxy%0A%60%60%60%0A%0ATo%20enable%20HAProxy%20change%20in%20**%2Fetc%2Fdefault%2Fhaproxy**%20to%0A%0A%60%60%60bash%0AENABLED%3D1%0A%60%60%60%0A%0AThen%2C%0A%0Achange%20in%20**%2Fetc%2Fhaproxy%2Fhaproxy.cfg**%0A%0A%60%60%60bash%0Adefaults%0Alog%20%20%20%20%20global%0Amode%20%20%20%20tcp%0Aoption%20%20tcplog%0A%60%60%60%0A%0AAnd%20add%0A%0A%60%60%60bash%0Afrontend%20mqtt%0A%20%20%20%20bind%200.0.0.0%3A1883%0A%20%20%20%20default_backend%20mqtt%0A%0Abackend%20mqtt%0A%20%20%20%20mode%20tcp%0A%20%20%20%20balance%20roundrobin%0A%20%20%20%20server%20node1%20node1.example.com%3A1883%20check%0A%20%20%20%20server%20node2%20node2.example.com%3A1883%20check%0A%0Afrontend%20mqtt_dashboard%0A%20%20%20%20bind%200.0.0.0%3A18083%0A%20%20%20%20default_backend%20mqtt_dashboard%0A%0Abackend%20mqtt_dashboard%0A%20%20%20%20mode%20http%0A%20%20%20%20balance%20roundrobin%0A%20%20%20%20server%20node1%20node1.example.com%3A18083%20check%0A%20%20%20%20server%20node2%20node2.example.com%3A18083%20check%0A%60%60%60%0A%0AAnd%20you%20are%20done.%0A%0ANow%20browse%20%5Bhttp%3A%2F%2Flb.example.com%3A18083%5D(http%3A%2F%2Flb.example.com%3A18083)%0A%0AMqtt%20URL%20%3A%20**tcp%3A%2F%2Flb.example.com%3A1883**%0A%0Ayou%20will%20see%20server%20are%20swapping.%0A%0AEmqttd%20dashboard%20default%0A%0A**user%20%3A%20admin%2C**%0A%0A**pass%20%3A%20public**

How to : Setup MQTT cluster with HAProxy

First%20time%20writing%20on%20Machine%20learning.%20In%20this%20post%20will%20discuss%20about%20text%20classification.%20We%20will%20use%20Naive%20Bayes%20Classifier%20for%20classification.%0A%0ALets%20start%2C%0A%0AOk%2C%20You%20may%20want%20to%20know%20what%20is%20classifier%20%3F%0A%0AWell%2C%20classifier%20classifies%20training%20data%20based%20on%20implemented%20algorithm%20as%20we%20are%20using%20Naive%20Bayes%20Classifier%20algorithm%20which%20is%20based%20on%20Bayes%20theorem.%20Naive%20Bayes%20Classifier%20works%20based%20on%20phrase%20frequency%20and%20its%20Supervised%20learning.%0A%0ALets%20assume%20Nur%20started%20using%20email%20and%20his%20relatives%2C%20teachers%2C%20friends%20are%20contacting%20via%20it.%20As%20well%20as%20he%20is%20using%20this%20email%20id%20in%20different%20social%20networks.%20As%20he%20is%20getting%20lots%20of%20email%20now%2C%20he%20want%20to%20categorize%20it%20so%20he%20can%20easily%20check%20emails%20from%20relatives%2C%20teachers%2C%20friends%20and%20others.%0A%0A!%5B%5D(http%3A%2F%2Fblog.sakib.ninja%2Fcontent%2Fimages%2F2017%2F02%2FScreen-Shot-2017-02-14-at-7.42.53-PM.png)%0A%0ANur%20has%20a%20MagicBox%20which%20is%20able%20to%20identify%20certain%20things%20based%20on%20preset%20data.%20So%20nur%20decides%20to%20take%20the%20help%20of%20magic%20box.%20So%20he%20started%20setting%20few%20key%20sentence%20and%20word%20based%20on%20which%20magic%20box%20will%20categorize%20emails.%0A%0AKey%20sentence%20and%20words%20are%20like%2C%0A%0A%5C%5BText%5C%5D%20%3D%3E%20%5C%5BLabel%5C%5D%0A%0Ayour%20aunty%20%3D%3E%20%5C%5Brelative%5C%5D%0A%0Adear%20friend%20%3D%3E%20%5C%5Bfriend%5C%5D%0A%0Afrom%20Jhalokathi%20%3D%20%5C%5Brelative%5C%5D%0A%0Ayour%20cousin%20%3D%3E%20%5C%5Brelative%5C%5D%0A%0ADear%20subscriber%20%3D%3E%20%5C%5Bsocial%5C%5D%0A%0Anew%20post%20%3D%3E%20%5C%5Bsocial%5C%5D%0A%0Anew%20homework%20%3D%3E%20%5C%5Bteacher%5C%5D%0A%0Ais%20weekend%20%3D%3E%20%5C%5Bteacher%5C%5D%0A%0Aclass%20teacher%20%5C%5Bteacher%5C%5D%0A%0AIn%20machine%20learning%20this%20are%20called%20training%20data.%0A%0ANow%20assume%20Nur%20got%20two%20email%2C%20Those%20are%2C%0A%0A**Hello%20nur%2C%20I%20am%20your%20class%20teacher%20Jessica.%20Tomorrow%20is%20weekend.%20So%20there%20is%20no%20homework.%20Enjoy%20the%20weekend.**%0A%0AAnd%0A%0A**Hello%20nur%2C%20I%20am%20Rupa%20your%20cousin.**%0A%0ANow%20lets%20check%20email%20category%20using%20Magic%20Box.%0A%0A!%5B%5D(http%3A%2F%2Fblog.sakib.ninja%2Fcontent%2Fimages%2F2017%2F02%2FScreen-Shot-2017-02-14-at-7.59.23-PM.png)%0A%0A!%5B%5D(http%3A%2F%2Fblog.sakib.ninja%2Fcontent%2Fimages%2F2017%2F02%2FScreen-Shot-2017-02-14-at-7.58.50-PM.png)%0A%0AOk%2C%20Nur%20got%20results%20from%20Magic%20Box%20and%20its%20correct.%0A%0ANurs%20Magic%20Box%20uses%20Naive%20Bayes%20Classifier%20algorithm%20to%20categorize%20data.%0A%0AIn%20supervised%20machine%20learning%20result%20accuracy%20depends%20on%20training%20data.%0A%0AUsed%20implementation%20of%20Naive%20Bayes%20Classifier%20%3A%20%5Bhttps%3A%2F%2Fgithub.com%2Fptnplanet%2FJava-Naive-Bayes-Classifier%5D(https%3A%2F%2Fgithub.com%2Fptnplanet%2FJava-Naive-Bayes-Classifier)%0A%0AExample%20%3A%0A%0A%60%60%60%0Aval%20bayesClassifier%20%3D%20BayesClassifier%3CString%2C%20String%3E()%0A%0A%2F%2F%20Learning%0Aval%20tokenizeSampleText%20%3D%20%22Sample%20Sentence%22.split(%22%20%22)%0Aval%20sampleLabel%20%3D%20%22SampleLabel%22%0AbayesClassifier.learn(sampleLabel%2C%20tokenizeSampleText)%0A%0A%2F%2F%20Classify%0Aval%20result%20%3D%20bayesClassifier.classify(%22QueryText%22.split(%22%20%22))%0Aprintln(%22Category%20%3A%20%24%7Bresult.category%7D%2C%20Probability%20%3A%20%24%7Bresult.probability%7D%22)%0A%0A%60%60%60%0A%0AMagic%20Box%20source%20code%20%3A%0A%0A%5Bhttps%3A%2F%2Fgithub.com%2Fs4kibs4mi%2Fmachine-learning-garage%5D(https%3A%2F%2Fgithub.com%2Fs4kibs4mi%2Fmachine-learning-garage)

ML : Nur & His Magic Box

First%20you%20should%20know%20what%20is%20kotlin.%0A%0AOk%2C%20Kotlin%20is%20a%20**JVM**%20based%20statically%20typed%20programming%20language%20developed%20by%20JetBrains.%0A%0ANow%20you%20may%20what%20to%20know%20whom%20are%20JetBrains%20%3F%0A%0AWell%2C%20JetBrains%20is%20the%20creator%20of%20Intellj%20Idea%2C%20PhyCharm%20%26%20few%20other%20awesome%20development%20tool.%0A%0ANote%20the%20word%20%60JVM%20based%60.%20This%20means%20kotlin%20runs%20on%20%60Java%20Virtual%20Machine%60.%0A%0ASurprised%20%3F%20If%20so%2C%20then%20you%20may%20want%20to%20know%20if%20Java%20%26%20Kotlin%20both%20runs%20on%20JVM%20then%20why%20people%20are%20so%20excited%20about%20Kotlin%20for%20Android.%0A%0AHmm%2C%20That%20is%20this%20post's%20discussion%20topic.%0A%0AI%20will%20figure%20out%20some%20points%20why%20people%20(Specially%20me)%20prefer%20Kotlin%20over%20Java.%0A%0AFew%20Short%20Note%20%3A%0A%0A-%5C%3E%20It's%20opensource.%0A%0A-%5C%3E%20Kotlin%20compiles%20to%20JVM%20bytecode%20or%20JavaScript.%0A%0A-%5C%3E%20Much%20smaller%20learning%20curve%20than%20any%20other%20jvm%20based%20language.%0A%0A-%5C%3E%20It%20imposes%20no%20runtime%20overhead.%0A%0A-%5C%3E%20Better%20IDE%20support.%0A%0A-%5C%3E%20Kotlin%20native%20to%20run%20kotlin%20application%20without%20JVM%20(not%20supported%20yet).%0A%0A**1%5C.%20I%20am%20a%20lazy%20guy**%20%3A%20As%20I%20am%20a%20very%20lazy%20I%20don't%20want%20to%20write%20unnecessary%20code.%0A%0ALike%2C%20Assume%20we%20are%20using%20a%20rest%20api%20in%20our%20app.%0A%0AHow%20we%20will%20call%20it%20from%20Java.%0A%0A%60%60%60java%0Apublic%20class%20UserApi%20%7B%0A%20%20%20%20public%20static%20Result%20callForLogin(String%20username%2C%20String%20password)%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%20Api%20call%20here%0A%20%20%20%20%7D%0A%7D%0A%0A%60%60%60%0A%0A%2F%2F%20calling...%0A%0A%60%60%60java%0AResult%20result%20%3D%20UserApi.callForLogin(%22sakib%22%2C%20%2212345%22)%3B%0A%0A%60%60%60%0A%0AHow%20we%20can%20do%20it%20in%20kotlin%20%3F%0A%0A%60%60%60kotlin%0A%2F%2F%20UserApi.kt%0A%2F%2F%20You%20don't%20have%20to%20create%20class%0A%0Afun%20callForLogin(username%3A%20String%2C%20password%3A%20String)%20%7B%0A%20%20%20%20%2F%2F%20Api%20call%20here%0A%7D%0A%0A%60%60%60%0A%0A%2F%2F%20calling...%0A%0A%60%60%60kotlin%0Aval%20result%20%3D%20callForLogin(%22sakib%22%2C%20%2212345%22)%0A%0A%60%60%60%0A%0A**2%5C.%20Extension%20function**%20%3A%20Assume%20you%20want%20to%20add%20few%20functionality%20in%20%60Integer%60%20or%20%60String%60%20class.%20What%20we%20will%20do%20in%20Java%20%3F%20You%20have%20nothing%20to%20do%20as%20String%20%26%20Integer%20is%20final%20class.%0A%0ABut%20in%20kotlin%20you%20can%20do%20it%20easily.%0A%0A%60%60%60%0Afun%20Int.str()%3A%20String%20%7B%0A%20%20%20%20when%20(this)%20%7B%0A%20%20%20%20%20%20%20%200%20-%3E%20return%20%22ZERO%22%0A%20%20%20%20%20%20%20%201%20-%3E%20return%20%22ONE%22%0A%20%20%20%20%20%20%20%202%20-%3E%20return%20%22TWO%22%0A%20%20%20%20%20%20%20%203%20-%3E%20return%20%22THREE%22%0A%20%20%20%20%20%20%20%204%20-%3E%20return%20%22FOUR%22%0A%20%20%20%20%20%20%20%205%20-%3E%20return%20%22FIVE%22%0A%20%20%20%20%20%20%20%20else%20-%3E%20return%20%22NOT%20IMPLEMENTED%22%0A%20%20%20%20%7D%0A%7D%0A%0A%60%60%60%0A%0Auses%2C%0A%0A%60%60%60%0Avar%20x%20%3D%201%0Aprintln(x.str())%20%20%20%20%2F%2F%20Output%20%3A%20ONE%0A%0A%60%60%60%0A%0A%60str()%60%20method%20is%20available%20to%20object%20of%20Int%20class.%20This%20is%20called%20extension%20function%20in%20kotlin.%0A%0A**3%5C.%20My%20App%20is%20full%20of%20Singletons**%20%3A%20How%20we%20implement%20Singleton%20pattern%20in%20Java%2C%0A%0A%60%60%60java%0Apublic%20class%20MySingleton%20%7B%0A%20%20%20%20public%20static%20MySingleton%20mySingleton%20%3D%20null%3B%0A%0A%20%20%20%20public%20static%20MySingleton%20getInstance()%7B%0A%20%20%20%20%20%20%20%20if(mySingleton%20%3D%3D%20null)%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20mySingleton%20%3D%20new%20MySingleton()%3B%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%0A%20%20%20%20private%20MySingleton()%20%7B%0A%0A%20%20%20%20%7D%0A%7D%0A%0A%60%60%60%0A%0Auses%2C%0A%0A%60%60%60java%0AMySingleton%20mySingleton%20%3D%20MySingleton.getInstance()%3B%0A%0A%60%60%60%0A%0ACool%20!%20How%20it%20will%20look%20like%20in%20kotlin%20%3F%0A%0A%60%60%60kotlin%0Aobject%20MySingleton%20%7B%0A%0A%7D%0A%0A%60%60%60%0A%0Auses%2C%0A%0A%60%60%60kotlin%0Aval%20mySingleton%20%3D%20MySingleton%0A%0A%60%60%60%0A%0AStill%20you%20hate%20Kotlin%20%3F%20Ok%2C%20Go%20scroll%20down.%0A%0A**4%5C.%20Operator%20overloading**%20%3A%20you%20can%20overload%20operators%20in%20Kotlin.%20Here%20is%20an%20example%2C%0A%0A%60%60%60kotlin%0Aoperator%20fun%20String.times(times%3A%20Int)%3A%20String%20%7B%0A%20%20%20%20val%20buffer%20%3D%20StringBuilder()%0A%20%20%20%20for%20(i%20in%201..times)%20%7B%0A%20%20%20%20%20%20%20%20buffer.append(this)%0A%20%20%20%20%20%20%20%20if%20(i%20%3C%20times)%0A%20%20%20%20%20%20%20%20%20%20%20%20buffer.append(%22%20%22)%0A%20%20%20%20%7D%0A%20%20%20%20return%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Why I perfer Kotlin over Java for Android

MQTT%20(Message%20Queue%20Telemetry%20Transport)%20is%20a%20lightweight%20messaging%20protocol%20specially%20designed%20for%20IOT%20by%20IBM.%20MQTT%20works%20on%20Publish-Subscribe%20Model.%0A%0AFacebook%20%26%20WhatsApp%20uses%20MQTT%20for%20their%20messaging%20engine.%0A%0AWell%2C%20In%20the%20tutorial%20I%20am%20going%20to%20show%20how%20you%20can%20implement%20a%20push%20notification%20service%20using%20MQTT.%20I%20am%20not%20going%20to%20implement%20complete%20service%20but%20a%20prototype%20on%20how%20it%20can%20be.%0A%0ATools%20will%20used%2C%0A%0A1.%20EMQ%20(MQTT%20Broker)%0A2.%20MongoDB%20(To%20store%20user's%20information)%0A3.%20Admin%20Dashboard%20(To%20publish%20notification)%0A4.%20Android%20App%20(Client)%0A5.%20Eclipse%20Paho%20MQTT%20client%20(Android%2C%20JavaScript)%0A%0A!%5B%5D(http%3A%2F%2Fblog.sakib.ninja%2Fcontent%2Fimages%2F2017%2F05%2FUntitled-Diagram.png)%0A%0AIts%20the%20big%20picture%2C%20how%20components%20in%20the%20system%20are%20interacting%20with%20each%20other.%0A%0A%3E%20The%20idea%20is%20user%20will%20connect%20to%20mqtt%20broker%2C%20broker%20will%20authenticate%20them%20with%20data%20in%20mongodb.%0A%3E%0A%3E%20Assume%20a%20user%20as%20system%20admin%20who%20will%20publish%20notifications%20%26%20other%20users%20will%20be%20subscribed%20to%20receive%20these%20notifications.%20Suppose%2C%20**%5Ba%40email.com%5D(mailto%3Aa%40email.com)**%20is%20a%20user%2C%20after%20authentication%20with%20the%20email%20address%20the%20user%20will%20be%20subscribed%20to%20the%20topic(%20**%5Ba%40email.com%5D(mailto%3Aa%40email.com)**)%20and%20then%20from%20admin%20dashboard%20if%20you%20publish%20a%20message%20on%20topic%20**%5Ba%40email.com%5D(mailto%3Aa%40email.com)**%20the%20user%20will%20receive%20it.%20Thats%20all.%0A%0AMongoDB%20Document%20Schema%2C%0A%0A%60%60%60%0A%7B%0A%20%20%20%20%22user_email%22%3A%20%22email%20address%20of%20user%22%2C%0A%20%20%20%20%22user_password%22%3A%20%22password%20of%20user%22%2C%0A%20%20%20%20%22type%22%3A%20%22admin%2Fuser%22%0A%7D%0A%0A%60%60%60%0A%0AAssume%20this%20is%20the%20admin%20dashboard%2C%0A%0A!%5B%5D(http%3A%2F%2Fblog.sakib.ninja%2Fcontent%2Fimages%2F2017%2F06%2FUntitled-Diagram.png)%0A%0AThere%20are%203%20buttons.%20One%20to%20**Logout**%2C%20One%20is%20to%20**Add%20User**%20and%20another%20to%20**Send%20Push**%20notifications.%0A%0AIn%20screen%20the%20push%20notification%20view%20is%20visible.%20Admin%20dashboard%20is%20connected%20to%20MQTT%20broker%20via%20Websocket.%20User%20Email%20Address%20is%20the%20topic%20where%20message%20is%20going%20to%20be%20published.%20When%20clicked%20on%20Send%20it%20will%20publish%20the%20message%20using%20Websocket.%0A%0ANow%20if%20the%20respective%20email%20address%20is%20connected%20%26%20subscribed%20to%20respective%20topic%20then%20the%20client%20will%20receive%20the%20message.%0A%0A**Note**%20%3A%20This%20is%20just%20a%20prototype%20for%20educational%20purpose%20not%20production%20ready.%20To%20use%20it%20in%20production%20system%20you%20have%20to%20implement%20security%20%26%20other%20tuning%20where%20needed.

Building custom push notification service with MQTT

World%20wide%20we%20are%20passing%20a%20critical%20time.%20Lots%20of%20people%20out%20there%20with%20no%20job%2C%20no%20money%2C%20and%20no%20food.%20Especially%20in%203rd%20world%20countries.%20The%20government%20is%20coming%20forward%20to%20help%20these%20people.%20In%20my%20country%20Bangladesh%2C%20Government%20is%20taking%20lots%20of%20initiative%20to%20cope%20up%20with%20the%20situation.%20But%20the%20people%20who%20really%20need%20the%20help%2C%20aren%E2%80%99t%20being%20benefited%2C%20because%20of%20corrupt%20middle-man%20and%20distributors.%20If%20we%20couldn%E2%80%99t%20build%20trust%20and%20transparency%20within%20the%20system%2C%20no%20matter%20how%20much%20initiative%20we%20take%20people%20won%E2%80%99t%20be%20benefited.%0A%0AI%20am%20going%20to%20write%20a%20prototype%20of%20a%20solution%20based%20on%20blockchain%20which%20would%20be%20able%20to%20keep%20the%20trust%20and%20transparency%2C%20and%20people%20will%20be%20benefited.%20If%20you%20can%E2%80%99t%20use%20technology%20for%20the%20well%20being%20of%20people%2C%20it%20doesn%E2%80%99t%20matter%20how%20strong%20technologically%20we%20are%2C%20all%20these%20things%20are%20useless.%0A%0A%23%23%23%20**The%20Idea**%0A%0A**We%20will%20develop%20a%20blockchain-based%20relief%20distribution%20system%20where%20the%20respected%20citizen%20can%20register%20with%20their%20phone%20number%20and%20NID.%20Then%20they%20will%20be%20able%20to%20request%20relief%20through%20the%20system.%20These%20requests%20will%20be%20available%20to%20the%20Govt.%20higher%20authority%20and%20Local%20Govt.%20organization%20(DC%2FUNO%2FPolice%20etc).%20Once%20the%20relief%20request%20got%20approval%20from%20the%20Govt.%20higher%20authority%2C%20the%20Local%20Govt.%20organization%20will%20distribute%20the%20relief%20to%20the%20respected%20citizen%20who%20requested%20it.%20Once%20the%20requested%20person%20received%20the%20relief%20he%2Fshe%20will%20be%20able%20to%20update%20relief%20request%20status%20to%20received.%20Hence%20we%20can%20ensure%20the%20actual%20person%20who%20is%20in%20need%20got%20the%20relief.%20The%20relief%20request%20information%20will%20be%20kept%20on%20blockchain%20and%20will%20be%20available%20publicly.%20So%20anyone%20can%20view%20how%20many%20people%20around%20the%20country%20requested%20for%20relief%20and%20how%20many%20people%20got%20it.%20In%20this%20way%20proper%20transparency%2C%20reliability%20could%20be%20maintained.**%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F2400%2F1*wafgMP4lVPnP-bcdKty21g.png)%0A%0A%23%23%23%20Why%20blockchain%3F%0A%0ABlockchain%20is%20an%20immutable%20distributed%20ledger%20were%20all%20the%20relief%20request%20data%20will%20be%20written%20and%20no%20one%20can%20alter%20these%20data.%20Anyone%20can%20have%20a%20copy%20of%20these%20data%20and%20if%20anyone%20tries%20to%20alter%20any%20of%20the%20chain%20data%2C%20then%20the%20complete%20chain%20will%20be%20in%20a%20corrupt%20state.%0A%0A%23%23%23%20How%20it%20will%20work%0A%0A**Step%201%3A**%20Citizens%20will%20register%20with%20Phone%2C%20NID%2C%20and%20other%20information.%20(Here%20Govt.%20help%20will%20be%20required%20to%20validate%20the%20NID%20information%20and%20have%20to%20ensure%20that%20one%20NID%20is%20registered%20for%20one%20user%20only).%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*R7ryPtUaSq_A4Cxw7-elZQ.png)%0A%0A**Step%202%3A**%20Citizens%20will%20login%20with%20Phone%20number%20%26%20OTP%20verification.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*J_lUm15T7NDa9rfxCGNOlw.png)%0A%0A**Step%203%3A**%20Citizens%20can%20send%20a%20new%20request%20for%20relief%20through%20the%20system.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*Y8Q8MObN53y-BHyHz09UIg.png)%0A%0A**Step%204%3A**%20Citizens%20will%20be%20able%20to%20see%20all%20of%20him%2Fher%20relief%20requests.%20And%20will%20be%20able%20to%20see%20the%20status%20of%20each%20request.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*7e3i8c9a8ezNU-fWa0nBng.png)%0A%0A**Step%205%3A**%20All%20these%20requests%20will%20be%20available%20to%20higher%20management%20authority%20and%20local%20govt.%20organisation%20(such%20as.%20DC%20office%2C%20UNO%20office%2C%20Police%2C%20etc)%20through%20a%20dashboard.%20They%20will%20be%20able%20to%20validate%2C%20see%20other%20requests%20of%20a%20specific%20user%2C%20which%20will%20help%20them%20to%20ensure%20that%20a%20single%20user%20is%20getting%20lots%20of%20relief.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*kWLkMXluckzb7UYGSbmzBg.png)%0A%0AAnd%20if%20it%20seems%20the%20requested%20user%20is%20eligible%20to%20get%20the%20relief%20then%20they%20can%20approve%20the%20request%20and%20allocate%20specific%20amount%20of%20requested%20item%20which%20will%20be%20distributed.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*OBDKxToRtOY5Li2t4NWSJA.png)%0A%0A**Step%206%3A**%20Once%20the%20request%20got%20the%20approval%20of%20higher%20management%20authority%2C%20the%20local%20govt.%20organization%20will%20distribute%20the%20relief%20to%20the%20requested%20user.%20So%20the%20request%20status%20will%20be%20delivered.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*skdD24KMHhFxLjDAdei6Zg.png)%0A%0A**Step%207%3A**%20After%20that%2C%20once%20the%20requested%20user%20got%20the%20relief%20they%20can%20update%20the%20status%20of%20the%20request%20to%20received.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*_Oj9xRdabuAARQ6jy_oiSA.png)%0A%0AHence%20we%20can%20ensure%20that%20the%20requested%20user%20got%20the%20relief%20and%20Govt.%20can%20also%20ensure%20how%20much%20relief%20they%20have%20approved%2C%20distributed%2C%20and%20received%20by%20a%20specific%20user%2Fcitizen.%0A%0A!%5B%5D(https%3A%2F%2Fcdn-images-1.medium.com%2Fmax%2F1600%2F1*ehLvblAyaQ9RjxYKyzzCQw.png)%0A%0AAll%20of%20these%20data%20will%20be%20publicly%20available%20on%20the%20blockchain%20and%20a%20public%20dashboard%20will%20be%20available%20where%20anyone%20can%20see%20how%20many%20people%20requested%20for%20relief%2C%20how%20many%20got%20approval%2C%20and%20how%20many%20got%20delivered%20in%20which%20are.

Blockchain-based relief distribution system for trust and transparency

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