Hi, Yunze:
Obviously, the `ServiceUrlProvider` config is redundant.
>
Agree. In fact, The client already provides the updateServiceUrl method,
which the user can use to implement a dynamic update service URL. As for
how the user implements it and how to close his resources, I think it can
be left to the user.
在 2023年1月19日 15:16:52 上，Yunze Xu <y...@streamnative.io.invalid> 写道：
> Hi all,
>
> Currently we have a `ServiceUrlProvider` interface to configure when
> constructing a PulsarClient in `ClientBuilder#serviceUrlProvider`.
> From the beginning, I thought the `getServiceUrl` method is called
> each time the service URL is used, e.g. topic metadata lookup.
> However, the `getServiceUrl` method is only called when constructing
> the PulsarClient object. To update the PulsarClient's internal service
> URL, `PulsarClient#updateServiceUrl` must be called. Therefore, if we
> want to implement a `ServiceUrlProvider` that retrieves the latest
> service URL from a database, I have to implement it like:
>
> ```java
> class DataBaseServiceUrlProvider implements ServiceUrlProvider {
>
> private final ScheduledExecutorService executor =
> Executors.newSingleThreadScheduledExecutor();
>
> @Override
> public void initialize(PulsarClient client) {
> executor.schedule(() -> {
> try {
> client.updateServiceUrl(readServiceUrlFromDB()/* a
> fake method */);
> } catch (PulsarClientException e) {
> throw new RuntimeException(e);
> }
> }, 1, TimeUnit.SECONDS);
> }
>
> @Override
> public String getServiceUrl() {
> return "pulsar://localhost:6650";
> }
>
> @Override
> public void close() {
> executor.shutdown();
> }
> }
> ```
>
> The key point is, if we didn't call `client.updateServiceUrl` and only
> modified the returned value of `getServiceUrl` periodically, the
> internal service URL would never be updated.
>
> Based on the provider above, the following two code snippets could be
> nearly the same.
>
> ```java
> var client = PulsarClient.builder().serviceUrlProvider(new
> DataBaseServiceUrlProvider()).build();
> /* ... */
> client.close();
> ```
>
> ```java
> var client =
> PulsarClient.builder().serviceUrl("pulsar://localhost:6650").build();
> var provider = new DataBaseServiceUrlProvider();
> provider.initialize(client);
> /* ... */
> provider.close();
> client.close();
> ```
>
> Obviously, the `ServiceUrlProvider` config is redundant.
>
> PIP-121 implements the `AutoClusterFailover` as the service URL
> provider. However, it also calls the following methods periodically:
> - PulsarClientImpl#updateAuthentication
> - PulsarClientImpl#updateTlsTrustCertsFilePath
>
> It's unnatural and intuitive to say a service URL provider could
> modify the internal states of `PulsarClient`, including:
> - the service URL
> - the authentication
> - the TLS trust certificate file
> - ...
>
> BTW, the implementation of PIP-121 [1] is different from the design [2].
>
> [1] https://github.com/apache/pulsar/pull/13316
> [2] https://github.com/apache/pulsar/issues/13315
>
> Thanks,
> Yunze
>
