Reg. custom sinks in Flink

classic Classic list List threaded Threaded
5 messages Options
Reply | Threaded
Open this post in threaded view
|

Reg. custom sinks in Flink

Meghashyam Sandeep V
Hi there,

I have a flink streaming app where my source is Kafka and a custom sink to
Cassandra(I can't use standard C* sink that comes with flink as I have
customized auth to C*). I'm currently have the following:

messageStream
        .rebalance()

        .map( s-> {

    return mapper.readValue(s, JsonNode.class);)

        .filter(//filter some messages)

        .map(

         (MapFunction<JsonNode, String>) message -> {

         getDbSession.execute("QUERY_TO_EXEC")

         })

private static Session getDbSession() {
    if(dbSession == null && store!=null) {
        dbSession = getSession();
    }

    return dbSession;
}

1. Is this the right way to add a custom sink? As you can see, I have
dbSession as a class variable here and I'm storing its state.

2. This setup works fine in a standalone flink (java -jar MyJar.jar).
When I run using flink with YARN on EMR I get a NPE at the session
which is kind of weird.


Thanks
Reply | Threaded
Open this post in threaded view
|

Re: Reg. custom sinks in Flink

Shannon Carey
You haven't really added a sink in Flink terminology, you're just performing a side effect within a map operator. So while it may work, if you want to add a sink proper you need have an object that extends SinkFunction or RichSinkFunction. The method call on the stream should be ".addSink(…)".

Also, the dbSession isn't really Flink state as it will not vary based on the position in or content in the stream. It's a necessary helper object, yes, but you don't need Flink to checkpoint it.

You can still use the sinks provided with flink-connector-cassandra and customize the cluster building by passing your own ClusterBuilder into the constructor.

-Shannon

From: Meghashyam Sandeep V <[hidden email]<mailto:[hidden email]>>
Date: Friday, December 9, 2016 at 12:26 PM
To: <[hidden email]<mailto:[hidden email]>>, <[hidden email]<mailto:[hidden email]>>
Subject: Reg. custom sinks in Flink

Hi there,

I have a flink streaming app where my source is Kafka and a custom sink to Cassandra(I can't use standard C* sink that comes with flink as I have customized auth to C*). I'm currently have the following:


messageStream
        .rebalance()

        .map( s-> {

    return mapper.readValue(s, JsonNode.class);)

        .filter(//filter some messages)

        .map(

         (MapFunction<JsonNode, String>) message -> {

         getDbSession.execute("QUERY_TO_EXEC")

         })

private static Session getDbSession() {
    if(dbSession == null && store!=null) {
        dbSession = getSession();
    }

    return dbSession;
}

1. Is this the right way to add a custom sink? As you can see, I have dbSession as a class variable here and I'm storing its state.

2. This setup works fine in a standalone flink (java -jar MyJar.jar). When I run using flink with YARN on EMR I get a NPE at the session which is kind of weird.


Thanks
Reply | Threaded
Open this post in threaded view
|

Re: Reg. custom sinks in Flink

Meghashyam Sandeep V
Thanks a lot for the quick reply Shannon.

1. I will create a class that extends SinkFunction and write my connection
logic there. My only question here is- will a dbSession be created for each
message/partition which might affect the performance? Thats the reason why
I added this line to create a connection once and use it along the
datastream. if(dbSession == null && store!=null) { dbSession =
getSession();}

2. I couldn't use flink-connector-cassandra as I have SSL enabled for my C*
cluster and I couldn't get it work with all my SSL
config(truststore,keystore etc) added to cluster building. I didn't find a
proper example with SSL enabled flink-connector-cassandra


Thanks




On Fri, Dec 9, 2016 at 10:54 AM, Shannon Carey <[hidden email]> wrote:

> You haven't really added a sink in Flink terminology, you're just
> performing a side effect within a map operator. So while it may work, if
> you want to add a sink proper you need have an object that extends
> SinkFunction or RichSinkFunction. The method call on the stream should be
> ".addSink(…)".
>
> Also, the dbSession isn't really Flink state as it will not vary based on
> the position in or content in the stream. It's a necessary helper object,
> yes, but you don't need Flink to checkpoint it.
>
> You can still use the sinks provided with flink-connector-cassandra and
> customize the cluster building by passing your own ClusterBuilder into the
> constructor.
>
> -Shannon
>
> From: Meghashyam Sandeep V <[hidden email]>
> Date: Friday, December 9, 2016 at 12:26 PM
> To: <[hidden email]>, <[hidden email]>
> Subject: Reg. custom sinks in Flink
>
> Hi there,
>
> I have a flink streaming app where my source is Kafka and a custom sink to
> Cassandra(I can't use standard C* sink that comes with flink as I have
> customized auth to C*). I'm currently have the following:
>
> messageStream
>         .rebalance()
>
>         .map( s-> {
>
>     return mapper.readValue(s, JsonNode.class);)
>
>         .filter(//filter some messages)
>
>         .map(
>
>          (MapFunction<JsonNode, String>) message -> {
>
>          getDbSession.execute("QUERY_TO_EXEC")
>
>          })
>
> private static Session getDbSession() {
>     if(dbSession == null && store!=null) {
>         dbSession = getSession();
>     }
>
>     return dbSession;
> }
>
> 1. Is this the right way to add a custom sink? As you can see, I have dbSession as a class variable here and I'm storing its state.
>
> 2. This setup works fine in a standalone flink (java -jar MyJar.jar). When I run using flink with YARN on EMR I get a NPE at the session which is kind of weird.
>
>
> Thanks
>
>
Reply | Threaded
Open this post in threaded view
|

Re: Reg. custom sinks in Flink

Till Rohrmann
Hi Meghashyam,

   1.

   You can perform initializations in the open method of the
   RichSinkFunction interface. The open method will be called once for
   every sub task when initializing it. If you want to share the resource
   across multiple sub tasks running in the same JVM you can also store the
   dbSession in a class variable.
   2.

   The Flink community is currently working on adding security support
   including ssl encryption to Flink. So maybe in the future you can use
   Flink’s Cassandra sink again.

Cheers,
Till


On Fri, Dec 9, 2016 at 8:05 PM, Meghashyam Sandeep V <
[hidden email]> wrote:

> Thanks a lot for the quick reply Shannon.
>
> 1. I will create a class that extends SinkFunction and write my connection
> logic there. My only question here is- will a dbSession be created for each
> message/partition which might affect the performance? Thats the reason why
> I added this line to create a connection once and use it along the
> datastream. if(dbSession == null && store!=null) { dbSession =
> getSession();}
>
> 2. I couldn't use flink-connector-cassandra as I have SSL enabled for my
> C* cluster and I couldn't get it work with all my SSL
> config(truststore,keystore etc) added to cluster building. I didn't find a
> proper example with SSL enabled flink-connector-cassandra
>
>
> Thanks
>
>
>
>
> On Fri, Dec 9, 2016 at 10:54 AM, Shannon Carey <[hidden email]> wrote:
>
>> You haven't really added a sink in Flink terminology, you're just
>> performing a side effect within a map operator. So while it may work, if
>> you want to add a sink proper you need have an object that extends
>> SinkFunction or RichSinkFunction. The method call on the stream should be
>> ".addSink(…)".
>>
>> Also, the dbSession isn't really Flink state as it will not vary based on
>> the position in or content in the stream. It's a necessary helper object,
>> yes, but you don't need Flink to checkpoint it.
>>
>> You can still use the sinks provided with flink-connector-cassandra and
>> customize the cluster building by passing your own ClusterBuilder into the
>> constructor.
>>
>> -Shannon
>>
>> From: Meghashyam Sandeep V <[hidden email]>
>> Date: Friday, December 9, 2016 at 12:26 PM
>> To: <[hidden email]>, <[hidden email]>
>> Subject: Reg. custom sinks in Flink
>>
>> Hi there,
>>
>> I have a flink streaming app where my source is Kafka and a custom sink
>> to Cassandra(I can't use standard C* sink that comes with flink as I have
>> customized auth to C*). I'm currently have the following:
>>
>> messageStream
>>         .rebalance()
>>
>>         .map( s-> {
>>
>>     return mapper.readValue(s, JsonNode.class);)
>>
>>         .filter(//filter some messages)
>>
>>         .map(
>>
>>          (MapFunction<JsonNode, String>) message -> {
>>
>>          getDbSession.execute("QUERY_TO_EXEC")
>>
>>          })
>>
>> private static Session getDbSession() {
>>     if(dbSession == null && store!=null) {
>>         dbSession = getSession();
>>     }
>>
>>     return dbSession;
>> }
>>
>> 1. Is this the right way to add a custom sink? As you can see, I have dbSession as a class variable here and I'm storing its state.
>>
>> 2. This setup works fine in a standalone flink (java -jar MyJar.jar). When I run using flink with YARN on EMR I get a NPE at the session which is kind of weird.
>>
>>
>> Thanks
>>
>>
>
Reply | Threaded
Open this post in threaded view
|

Re: Reg. custom sinks in Flink

Meghashyam Sandeep V
Hi Till,

Thanks for the information.

1. What do you mean by 'subtask', is it every partition or every message in
the stream?

2. I tried using CassandraSink with a Pojo. Is there a way to specify TTL
as I can't use a query when I have a datastream with Pojo?

CassandraSink.addSink(messageStream)
         .setClusterBuilder(new ClusterBuilder() {
             @Override
             protected Cluster buildCluster(Cluster.Builder builder) {
                 return buildCassandraCluster();
             }
         })
         .build();


Thanks,


On Mon, Dec 12, 2016 at 3:17 AM, Till Rohrmann <[hidden email]> wrote:

> Hi Meghashyam,
>
>    1.
>
>    You can perform initializations in the open method of the
>    RichSinkFunction interface. The open method will be called once for
>    every sub task when initializing it. If you want to share the resource
>    across multiple sub tasks running in the same JVM you can also store the
>    dbSession in a class variable.
>    2.
>
>    The Flink community is currently working on adding security support
>    including ssl encryption to Flink. So maybe in the future you can use
>    Flink’s Cassandra sink again.
>
> Cheers,
> Till
> ​
>
> On Fri, Dec 9, 2016 at 8:05 PM, Meghashyam Sandeep V <
> [hidden email]> wrote:
>
>> Thanks a lot for the quick reply Shannon.
>>
>> 1. I will create a class that extends SinkFunction and write my
>> connection logic there. My only question here is- will a dbSession be
>> created for each message/partition which might affect the performance?
>> Thats the reason why I added this line to create a connection once and use
>> it along the datastream. if(dbSession == null && store!=null) { dbSession
>> = getSession();}
>>
>> 2. I couldn't use flink-connector-cassandra as I have SSL enabled for my
>> C* cluster and I couldn't get it work with all my SSL
>> config(truststore,keystore etc) added to cluster building. I didn't find a
>> proper example with SSL enabled flink-connector-cassandra
>>
>>
>> Thanks
>>
>>
>>
>>
>> On Fri, Dec 9, 2016 at 10:54 AM, Shannon Carey <[hidden email]>
>> wrote:
>>
>>> You haven't really added a sink in Flink terminology, you're just
>>> performing a side effect within a map operator. So while it may work, if
>>> you want to add a sink proper you need have an object that extends
>>> SinkFunction or RichSinkFunction. The method call on the stream should be
>>> ".addSink(…)".
>>>
>>> Also, the dbSession isn't really Flink state as it will not vary based
>>> on the position in or content in the stream. It's a necessary helper
>>> object, yes, but you don't need Flink to checkpoint it.
>>>
>>> You can still use the sinks provided with flink-connector-cassandra and
>>> customize the cluster building by passing your own ClusterBuilder into the
>>> constructor.
>>>
>>> -Shannon
>>>
>>> From: Meghashyam Sandeep V <[hidden email]>
>>> Date: Friday, December 9, 2016 at 12:26 PM
>>> To: <[hidden email]>, <[hidden email]>
>>> Subject: Reg. custom sinks in Flink
>>>
>>> Hi there,
>>>
>>> I have a flink streaming app where my source is Kafka and a custom sink
>>> to Cassandra(I can't use standard C* sink that comes with flink as I have
>>> customized auth to C*). I'm currently have the following:
>>>
>>> messageStream
>>>         .rebalance()
>>>
>>>         .map( s-> {
>>>
>>>     return mapper.readValue(s, JsonNode.class);)
>>>
>>>         .filter(//filter some messages)
>>>
>>>         .map(
>>>
>>>          (MapFunction<JsonNode, String>) message -> {
>>>
>>>          getDbSession.execute("QUERY_TO_EXEC")
>>>
>>>          })
>>>
>>> private static Session getDbSession() {
>>>     if(dbSession == null && store!=null) {
>>>         dbSession = getSession();
>>>     }
>>>
>>>     return dbSession;
>>> }
>>>
>>> 1. Is this the right way to add a custom sink? As you can see, I have dbSession as a class variable here and I'm storing its state.
>>>
>>> 2. This setup works fine in a standalone flink (java -jar MyJar.jar). When I run using flink with YARN on EMR I get a NPE at the session which is kind of weird.
>>>
>>>
>>> Thanks
>>>
>>>
>>
>