Add readme

Fixes elcallio#1

README.md

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+# kraken-dynamo
+originally base on this example:
+https://docs.amazonaws.cn/en_us/amazondynamodb/latest/developerguide/Streams.KCLAdapter.Walkthrough.html
+
+Re-written to use only Amazon SDK v2 async dynamo streams interfaces, to bypass SDK v1/kinesis poor 
+handling of large number of stream shards.
+
+This project is split into two modules, since it requires a patched (forked) version of the scylla
+dynamo load balancer. Actual program is in the "syncer" module.
+
+### example of how to run it
+```
+docker run -d -p 8080:8080 -p 9042:9042 scylladb/scylla-nightly:4.4.dev-0.20201217.a60c81b61 --alternator-port 8080 --alternator-write-isolation always --experimental 1
+# wait for scylla to be ready
+
+# run the KCL example
+# (in top level dir)
+maven install
+#in "syncer" module
+maven exec:java -Dexec.args="-e http://localhost:8080 -t usertable -k 1000"
+
+# (or to build a fat jar with all dependecies built in - in top level)
+maven package
+# will generate a syncer/target/kraken-dynamo-syncer-<version>-SNAPSHOT-jar-with-dependencies
+# that can be executed with simple java -jar
+
+# after ~30sec when tables created run ycsb
+
+
+# running with local ycsb
+python2.7 ./bin/ycsb load dynamodb  -P workloads/workloada -P dynamodb.properties -p recordcount=1000 -p insertorder=uniform -p insertcount=1000 -p fieldcount=2 -p fieldlength=50 -s
+
+# running with docker ycsb [keep in mind you localhost won't work inside docker, and you need a real address of you network interface]
+echo "accessKey=" > aws_dummy
+echo "secretKey=" >> aws_dummy
+docker run -v `pwd`/aws_dummy:/YCSB/aws_dummy -w /YCSB scylladb/hydra-loaders:ycsb-jdk8-20200326 ./bin/ycsb load dynamodb  -P workloads/workloada \
+ -p dynamodb.endpoint=http://192.168.122.1:8080 -p dynamodb.primaryKey=p -p dynamodb.awsCredentialsFile=aws_dummy \
+ -p recordcount=10000 -p insertorder=uniform -p insertcount=1000 -p fieldcount=2 -p fieldlength=50 -s
+
+
+# when you want to clear it out and try again
+cqlsh> DROP KEYSPACE "alternator_streams-demo"; DROP KEYSPACE "alternator_streams-demo-dest";
+```
+
+###
+```bash
+export KCL_DOCKER_IMAGE=scylladb/hydra-loaders:kcl-jdk8-$(date +'%Y%m%d')
+docker build . -t ${KCL_DOCKER_IMAGE}
+docker push ${KCL_DOCKER_IMAGE}
+echo "${KCL_DOCKER_IMAGE}" > image
+```
+
+### TODOs
+
+* [x] - dockerize it for usage in SCT
+