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Cassandra Proxy

A dual write proxy for Cassandra to aid in data migrations.

Features

This proxy handles client connections and forwards them to two Cassandra Clusters simultaneously. The idea is that writes will be delivered to both clusters thus allowing migrations without implementing dual write in the application.

Note:

  • The proxy proxies between two servers in a respective cluster. For optimal performance it is advised to run multiple proxies.
  • setting --wait to false will cause the proxy to not wait for a result from both servers but return once it gets a result from the source sever. This obviously can lead to botched migrations if the request never reaches the target server for any reason.

Quickstart

(Add steps to get up and running quickly assuming you have java and maven installed)

  1. git clone https://github.com/Azure-Samples/cassandra-proxy.git
  2. cd cassandra-proxy
  3. mvn package
  4. java -jar target/cassandra-proxy-1.0-SNAPSHOT-fat.jar source-server destination-server
  5. cqlsh -u user -p password localhost 29042

Docker

If you uncomment the jib plugin in the pom.xml mvn package will also create a (local) docker image. To use this run docker run cosmos.microsoft.com/cassandra-proxy source destination. You can push it to an adequate registry if needed on a different server.

Monitoring

The system will log through slf4j/logback and thus allow customization of logs as needed

Metrics

The system is using micrometer and provides a Prometheus compatible endpoint. Because micrometer is pluggable other metric aggregators could easily be supported if needed.

The metrics gathered are:

metric type Description
cassandraProxy.cqlOperation.proxyTime nanoseconds time spend solely for proxy processing
cassandraProxy.cqlOperation.timer nanoseconds time spend for the whole request (includes waiting for a response from both C* servers)
cassandraProxy.cqlOperation.cqlServerErrorCount counter counts the occurrence of error responses from the server and proxy
cassandraProxy.cqlOperation.cqlDifferentResultCount counter counts when the result of the same cql operation differed between the servers
cassandraProxy.clientSocket.paused nanoseconds time we need to pause requests to give the client time to catch up
cassandraProxy.serverSocket.paused nanoseconds time we need to pause requests to give Cassandra time to catch up

Some also contain tags indicating the opcode from the CQL protocol and a more readable form describing the request (e.g. Query).

The pause metrics also include a server or client address and in the case of the server a user defined identifier.

Future Plans

  • Read Reports
  • More robust TLS
  • better docs
  • ...

Migration

  1. Run the proxy
  2. Use any offline migration, e.g. Spark, sstableloader, or other.
  3. TBD: Retrieve read reports from proxy and see how close the results are

Known Issues

  • The data centers need to be named the same (which is an issue with loadbalancing clients beginning 4.0)
    • This is especially difficult for schema changes
  • Metrics are WIP - we noticed that some C* versions/implementations pad results differently
  • TLS on the backend servers doesn't do hostname validation nor client certs nor...
  • Proxy needs to run on the same host as the source Cassandra if errors and crazyness needs to be avoided

Resources

TBD