adding Cassandra as sink in Flink error : All host(s) tried for query failed - cassandra

Question

I was following up with an example at https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/connectors/cassandra.html to connect Cassandra as sink in Flink
My code for is shown below
public class writeToCassandra {
private static final String CREATE_KEYSPACE_QUERY = "CREATE KEYSPACE test WITH replication= {'class':'SimpleStrategy', 'replication_factor':1};";
private static final String createTable = "CREATE TABLE test.cassandraData(id varchar, heart_rate varchar, PRIMARY KEY(id));" ;
private final static Collection<String> collection = new ArrayList<>(50);
static {
for (int i = 1; i <= 50; ++i) {
collection.add("element " + i);
}
}
public static void main(String[] args) throws Exception {
//setting the env variable to local
StreamExecutionEnvironment envrionment = StreamExecutionEnvironment.createLocalEnvironment(1);
DataStream<Tuple2<String, String>> dataStream = envrionment
.fromCollection(collection)
.map(new MapFunction<String, Tuple2<String, String>>() {
final String mapped = " mapped ";
String[] splitted;
#Override
public Tuple2<String, String> map(String s) throws Exception {
splitted = s.split("\\s+");
return Tuple2.of(
UUID.randomUUID().toString(),
splitted[0] + mapped + splitted[1]
);
}
});
CassandraSink.addSink(dataStream)
.setQuery("INSERT INTO test.cassandraData(id,heart_rate) values (?,?);")
.setHost("127.0.0.1")
.build();
envrionment.execute();
} //main
} //writeToCassandra
I am getting the following error
Caused by: com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: /127.0.0.1:9042 (com.datastax.driver.core.exceptions.TransportException: [/127.0.0.1] Cannot connect))
at com.datastax.driver.core.ControlConnection.reconnectInternal(ControlConnection.java:231)

Answer 1

Not sure if this is always required, but the way that I set up my CassandraSink is like this:
CassandraSink
.addSink(dataStream)
.setClusterBuilder(new ClusterBuilder() {
#Override
protected Cluster buildCluster(Cluster.Builder builder) {
return Cluster.builder()
.addContactPoints(myListOfCassandraUrlsString.split(","))
.withPort(portNumber)
.build();
}
})
.build();
I have annotated POJOs that are returned by the dataStream so I don't need the query, but you would just include ".setQuery(...)" after the ".addSink(...)" line.

Answer 2

The exception simply indicates that the example program cannot reach the C* database.
flink-cassandra-connector offers streaming API to connect to designated C* database. Thus, you need to have a C* instance running.
Each streaming job is pushed/serialized to the node that Task Manager runs at. In your example, you assume C* is running on the same node as the TM node. An alternative is to change the C* address from 127.0.0.1 to a public address.