Just want to chime in here that it would be fantastic to have a way to DI
in Flink. Ideally the injected services themselves don't get serialized at
all since they're just singletons in our case. E.g. we have an API client
that looks up data from our API and caches it for all the functions that
need it.
On Tue, Nov 3, 2020 at 12:32 AM Arvid Heise <ar...@ververica.com> wrote:
> Hi Santhosh,
>
> Flink does not support automatic DI on task level and there is no
> immediate plan as of now to support it out-of-the-box. In general, there
> are quite a few implications of using automatic DI in a distributed
> setting. For example, how is a singleton supposed to work? Nevertheless,
> Flink's job startup got overhauled in the last and the upcoming release, so
> it might be easier to support DI frameworks in the near future.
>
> What I usually recommend is to use automatic DI while creating the
> DataStream application and then switch to manual DI on task manager level
> (most folks confuse DI with automatic DI, but DI is a general pattern that
> is independent of any framework).
>
> Here is an example. Suppose you want to use ServiceA in some asyncIO call.
>
> DataStream<Integer> inputStream = env.addSource(...);
> AsyncFunction<Integer, String> function = new ExternalLookupFunction();
> AsyncDataStream.unorderedWait(inputStream, function, 1,
> TimeUnit.SECONDS).print();
>
> class ExternalLookupFunction extends AsyncFunction<Integer, String> {
> @Autowired
> ServiceA service; // <-- will be injected wherever the DataStream graph
> is created
>
> @Override
> public void asyncInvoke(Integer input, ResultFuture<String>
> resultFuture) throws IOException {
> service.call(input, resultFuture::complete); // <-- called only
> on task manager
> }
> }
>
>
> Now the question is how ServiceA is transferred from client/job manager to
> task manager. One solution is to make ServiceA Serializable and just let
> Java Serialization handle everything automatically. Alternatively, you can
> only serialize the configuration information and create the service on
> RichAsyncFunction#open.
>
> Let's see if someone else made progress on providing the initialization
> hooks as described in your linked thread. Note that the community is busy
> getting Flink 1.12 done, so it might take a while for more answers.
>
> Best,
>
> Arvid
>
> On Tue, Nov 3, 2020 at 12:03 AM santhosh venkat <
> santhoshvenkat1...@gmail.com> wrote:
>
>>
>> Hi,
>>
>> I'm trying to integrate a dependency injection framework with flink
>> within my company. When I searched the user-mailing list, I found the
>> following thread in flink which discussed about this in the past:
>> http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Dependency-Injection-and-Flink-td18880.html
>>
>> Since the thread was ~2 yrs old, I'm creating this request.
>>
>> 1. How do we expect users to integrate flink with a dependency injection
>> framework. Are there any hooks/entry-points that we can use to seamlessly
>> integrate a DI-fwk with flink? How does the community recommend the
>> dependency injection integration?
>>
>> 2. Would it be possible to create the object(say spring objects) at a
>> flink-task scope ? Or all these objects(say spring) from a dependency
>> injection fwk are expected to be created at an entire process(JM/TM) level?
>>
>> Can someone please help answer the above questions and help me understand
>> the flink-guarantees better. Any help would be greatly appreciated.
>>
>> Thanks.
>>
>
>
> --
>
> Arvid Heise | Senior Java Developer
>
> <https://www.ververica.com/>
>
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