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https://github.com/instaclustr/cassandra-everywhere-strategy

An EverywhereStrategy implementation for Apache Cassandra. Useful for performing DSE Cassandra to Apache Cassandra migrations.
https://github.com/instaclustr/cassandra-everywhere-strategy

apache-cassandra bootstrap cassandra cluster datastax dse dse-cassandra everywhere migration netapp-public replication strategy topology

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An EverywhereStrategy implementation for Apache Cassandra. Useful for performing DSE Cassandra to Apache Cassandra migrations.

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README 

        
# Instaclustr Everywhere Strategy - Migrate from DSE to Apache Cassandra



Website: https://www.instaclustr.com/



Documentation: https://www.instaclustr.com/support/documentation/



[![Bintray Badge](https://img.shields.io/bintray/v/instaclustr/debian/instaclustr-everywhere-strategy.svg)](https://bintray.com/instaclustr/debian/instaclustr-everywhere-strategy)



An `EverywhereStrategy` implementation for Apache Cassandra.



This is useful for performing DSE Cassandra → Apache Cassandra migrations.



The remainder of this README refers to _DSE Cassandra_ as simply _DSE_, and _Apache Cassandra_ as _Cassandra_.



Simply install the JAR into the classpath on all Cassandra nodes. The JAR contains an implementation of `EverywhereStrategy` that

is compatible with Cassandra.



## Installation



### Cassandra Package Installs



We offer a packaged version of `instaclustr-everywhere-strategy` for systems where Cassandra has been installed via the official Apache.org Debian or RPM package.



This package will automatically install `instaclustr-everywhere-strategy` into an appropriate location for the Cassandra package install

(i.e. `$CASSANDRA_HOME/lib`, which at present is `/usr/share/cassandra/lib`).



_Note_: These packages have a hard dependency for a `cassandra` package.

If Cassandra hasn't been installed via your distributions package manager, installing `instaclustr-everywhere-strategy`

may force the Cassandra package to be installed. This may conflict with a tarball install.

See [Cassandra Tarball Installs](#cassandra-tarball-installs) below on how to install `instaclustr-everywhere-strategy`

for tarball installs of Cassandra.



#### Debian-Based Distributions



(Debian, Ubuntu, et al.)



1. Add the `instaclustr/debian` repository.



       echo "deb https://dl.bintray.com/instaclustr/debian stable main" > \

           /etc/apt/sources.list.d/instaclustr.sources.list

    

2. Run `apt-get update` to fetch the contents of the new package repository.



3. Run `apt-get install instaclustr-everywhere-stratgey` to install the package.



#### RPM-Based Distributions



(RHEL, Fedora, CentOS, et al.)



1. Add the `instaclustr/rpm` repository.



       wget -O - https://bintray.com/instaclustr/rpm/rpm | \

           sudo tee /etc/yum.repos.d/instaclustr.repo



2. Run `dnf install instaclustr-everywhere-strategy` to install the package.



    Hint: For YUM-based distributions the command is `yum install instaclustr-everywhere-strategy`.



### Cassandra Tarball Installs



1. Download the latest `instaclustr-everywhere-strategy` JAR from the [releases](https://github.com/instaclustr/everywhere-strategy/releases) page.



2. Install the `instaclustr-everywhere-strategy` JAR into the Cassandra classpath.



    Typically the best location is `$CASSANDRA_HOME/lib`.



3. Restart Cassandra.



## Testing



Some automated tests leveraging [Cassandra Cluster Manager](https://github.com/riptano/ccm) (CCM) exist in the

[`test/`](test/) directory.



The basic gist of testing is as follows:



1. Create a new keyspace using `EverywhereStrategy`:



       CREATE KEYSPACE example USING replication = {'class': 'EverywhereStrategy'};



    The strategy is installed correctly if the keyspace is created successfully.



1. Create a table under the new keyspace, and insert some data:



       CREATE TABLE example.demo (a text PRIMARY KEY);

       INSERT INTO example.demo (a) VALUES ('a');

       INSERT INTO example.demo (a) VALUES ('b');

       INSERT INTO example.demo (a) VALUES ('c');

       INSERT INTO example.demo (a) VALUES ('d');



    The strategy is functioning correctly if the data is replicated to all nodes.

    

1. Run `nodetool flush` on every node.



1. Run `nodetool compact` on every node.



1. Run `sstabledump` on the table SSTables from each node.



1. Compare the JSON output from each node and confirm that the data in each dump is identical.



See [DSE → Cassandra Migration Test Results](test/dse-migrate-test-results.md) for the results of running the

DSE → Cassandra end-to-end tests.



## Motivation



DSE uses an internal `EverywhereStrategy` implementation for various `dse_*` keyspaces.

When joining a Cassandra node to a DSE cluster these keyspaces will cause `ClassNotFound` exceptions to be thrown on the Cassandra node.

These exceptions result in a schema disagreement. 



In the `system.log` for a Cassandra node:



    ERROR [InternalResponseStage:1] MigrationTask.java:95 - Configuration exception merging remote schema

    org.apache.cassandra.exceptions.ConfigurationException: Unable to find replication strategy class 'org.apache.cassandra.locator.EverywhereStrategy'

        



and `nodetool describecluster`:



    Cluster Information:

    	Name: test-cluster

    	Snitch: org.apache.cassandra.locator.GossipingPropertyFileSnitch

    	DynamicEndPointSnitch: enabled

    	Partitioner: org.apache.cassandra.dht.Murmur3Partitioner

    	Schema versions:

    		850859e7-fcca-3516-9d8c-e9a9a205c974: [127.0.0.1, 127.0.0.2, 127.0.0.3]

    

    		e84b6a60-24cf-30ca-9b58-452d92911703: [127.0.1.1, 127.0.1.2, 127.0.1.3]

    		

In the output above, IPs `127.0.0.*` are DSE nodes, `127.0.1.*` are Cassandra nodes.



One common solution is to `ALTER` the `dse_*` keyspaces to use `NetworkTopologyStrategy` before joining Cassandra nodes to the cluster.

While this works, it's also dangerous.

DSE nodes reset the replication strategy back to `EverywhereStrategy` on startup.

As a result, if any DSE nodes restart while Cassandra nodes are present in the cluster then schema disagreement will again occur. 



## Implementation



Our `EverywhereStrategy` implementation extends `NetworkTopologyStrategy`.

This is required because various core components inside Cassandra

(e.g. [`ConsistencyLevel`](https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/db/ConsistencyLevel.java))

perform `instanceof NetworkTopologyStrategy` checks when they need to be data center aware.



Yet, `NetworkTopologyStrategy` hasn't been designed to be extendable.

A number of its fields are private final immutable, including `datacenters`, which is the DC→RF mapping.

So we resort to reflection to fix this. Yuck! But, it works…



## Version Compatibility



| Cassandra Version | Status |

| --- | --- |

| 4.x | Supported |

| 3.11.x | Supported |

| 3.0.x | Supported |

| 2.2.x | Supported |

| 2.1.x | Supported |

| 2.0.x | Supported |



For 2.1.x and 2.0.x versions, you can use version 2.2.x, it is compatible.



## License



This project is licensed under the Apache License, version 2.0. See [LICENSE](LICENSE) for details.



## Instaclustr Support



Please see our [Open Source Project Status](https://www.instaclustr.com/support/documentation/announcements/instaclustr-open-source-project-status/) page for details on Instaclustr's support status of this project.